Transcript Hydrocarbons and Fuels

Nature’s Chemistry
Organic Chemistry
In this unit traditional organic chemistry is studied
in the context of a wide range of everyday
consumer goods. The chemistry of the important
functional groups within these substances is
emphasised, as are the characteristic chemical
reactions.
Nature’s Chemistry
Organic Chemistry
From previous work you should know and understand the following:
•That molecular structure and physical properties of hydrocarbons are
related.
•The names, molecular and structural formula of alkanes (C1-C8),
alkenes (C2-C8) and cycloalkanes (C3-C8) straight and branched.
•How to identify isomers and draw their structural formulae.
•What is meant by saturated and unsaturated carbon compounds and
how they can be distinguished.
•Addition reactions
Nature’s Chemistry
Organic Chemistry
From previous work you should know and understand the following:
•Alcohols functional group –OH and properties of alcohols
•The names, molecular and structural formula of alcohols (C1-C8),
straight and branched.
•Carboxylic acids functional group COOH and properties of carboxylic
acids
•The names, molecular and structural formula of carboxylic acids (C1C8), straight and branched.
Organic Chemistry
Originally, chemical compounds were divided into 2 classes:
Inorganic or Organic
Organic compounds were derived from living things. It
was believed that they contained a ‘vital force’ and could
not be made from inorganic compounds (non-living sources).
Organic chemistry is the study of carbon compounds
Organic Chemistry
Organic chemistry is basically the study of compounds
containing carbon (with the exclusion of oxides and
carbonates).
There are so many compounds containing carbon that a
whole branch of chemistry is devoted to their study.
Organic molecules may be
as simple as methane, CH4
or as complicated as
cholesterol
HO
Fruity Flavours
Overview
In this section, learn about the
characteristic chemistry and uses
of esters, and find out how they
are made by condensation
reactions and broken down by
hydrolysis.
a) Esters
Learning intention
Learn how esters are named and
identified and how to draw the
structural formula of an ester.
Esters
Esterification, Alkanoic acids reacting with Alkanols.
Alcohol + Carboxylic Acid  Ester + Water
H+
Esters have sweet smells and are more volatile than carboxylic acids.
They are responsible for sweet fruit smells.
280 aromas make up a strawberry smell!!
•3-methylbutyl ethanoate in bananas.
•2-aminobenzoate is found in grapes.
We imitate these smells by manufacturing flavourings.
•Esters are also used in perfumes.
•Esters can also be used as solvents in glues.
•Polyesters are used to make plasticisers.
•Methyl ester is a biodiesel.
Naming Esters
R-yl
R-OH + R’-COOH  R’-COOR + Water
First, the 1st word comes from
the alcohol. The name ends in –yl.
Second
First
O
C2H5
C
O C2H5
CH3 CH2 COO CH2 CH3
ethyl propanoate
R’-oate
Second, find the C=O in the
carboxylate group, this gives the
2nd word with the ending –oate.
This comes from the acid.
Naming carboxylic acids and esters
Advice from the BBC on naming organic
compounds.
b) Making Esters
Learning intention
Learn about how esters are
formed by condensation reactions
of carboxylic acids and alcohols.
Making Esters
One way of preparing esters is to condense an alcohol with a carboxylic
acid:
O
O
C
R
O
alcohol
H
+
H
O
carboxylic acid
R'
C
R
R'
+ H 2O
O
ester
The reaction is slow at room temperature and the yield of ester is low. The
rate can be increased by heating the reaction mixture and by using
concentrated sulphuric acid as a catalyst. The presence of the concentrated
sulphuric acid also increases the yield of ester.
The aim of this experiment is to prepare an ester and to identify some of the
characteristic properties of esters.
Ester formation
Condensation Reaction
O
R C
O
+
O
R
H
O
R
O
C
+
R
O
H
H
Ester link
H
O
R
R
C
O
CH3COOH + CH3OH
ethanoic acid
methanol
CH3COOCH3 + H20
methyl ethanoate
The reaction is brought about by heating a mixture of a carboxylic acid
and an alcohol with a little concentrated sulphuric acid. (which acts as a
Catalyst and absorbs the water produced).
Animation esterification
Making esters
Procedure
Decide which alcohol and carboxylic acid you need to make each ester in the
table.
1. Before collecting the alcohol and carboxylic acid set up a water bath using
the larger beaker and heat the water until it boils. Turn off the Bunsen.
2. Add the alcohol to a test tube to a depth of about 1 cm. To this add
about the same volume of carboxylic acid. If the acid is a solid then use a
spatulaful.
3.In the interests of safety your teacher/lecturer may carry out the next
step.
Add about 5 drops of concentrated sulphuric acid to the reaction mixture.
Making esters
4. Soak the paper towel in cold water, fold it up and wrap it round the neck of
the test tube. Secure it with a rubber band. This arrangement acts as a
condenser when the reaction mixture is being heated.
5. Place a loose plug of cotton wool in the mouth of the test tube. This will
contain any chemicals which may spurt out of the reaction mixture when it is
heated.
6.Place the test tube in the hot water bath
Making esters
7. While the reaction mixture is being heated add about 20 cm3 of
sodium hydrogencarbonate solution to the small beaker.
8. After about 10 minutes, take the test tube from the water bath and
remove the plug of cotton wool. Slowly pour the reaction mixture
into the sodium hydrogencarbonate solution. This neutralises the
sulphuric acid and any remaining carboxylic acid and so removes the
smell of the carboxylic acid.
9. Gently swirl the contents of the beaker and look to see if there is any
sign of the ester separating from the aqueous mixture.
10. To smell the ester with your nose at least 30 cm from the mouth of
the beaker gently waft the vapour towards your nose and take just a
sniff.
c) Uses of Esters
Learning intention
Learn about the many everyday
uses of esters.
Uses of esters
Esters are oily liquids with generally very pleasant fruity smells and have a
range of uses.
Many esters are used as flavourings and in perfumes.
Natural fruit flavours contain subtle blends of some of the esters in the table
below:
Name
Methyl Butanoate
3-Methylbutyl Butanoate
Methyl-1-butyl ethanoate
2-Methylpropyl methanoate
Benzyl ethanoate
Ethyl methanoate
Methyl 2-aminobenzoate
Benzyl butanoate
Shortened Structural Formula Odour/Flavour
CH3(CH2)4CH3
Banana
CH3(CH)7CH3
Pineapple
CH3(CH2)2(CH2)2CH(CH3)2
Apple
CH3COOC3H7
Pear
CH3COOCH(CH3)C4H9
Banana
Raspberry
C3H7COOC5H11
Apricot, Strawberry
CH3COOCH2C6H5
Peach, flowers
C6H4(NH2)COOCH3
C3H7COOCH2C6H5
Grapes
Cherry
Uses of esters
Factors affecting perfume design e.g. using esters:
Designing a perfume - several issues to address by way
of design factors.
The perfume needs to be a mixture of compounds to
give a prolonged perfumery effect.
The perfumer chemist has to design the mixture to give
a particular fragrance which includes ...
the top note - the first fragrant molecule to be
released,
and the low note, the last molecule to be vapourised.
Uses of esters
Esters are also used as non-polar industrial solvents.
Some of the smaller esters are quite volatile and
are used as solvents in adhesives, inks and paints –
pentyl ethanoate is used in nail varnish for example.
Uses of esters
Ethyl ethanoate is one of a number of solvents used
to extract caffeine from coffee and tea.
De-caffeinated products produced with ethyl
ethanoate are often described on the packaging as
"naturally decaffeinated" because ethyl ethanoate
is a chemical found naturally in many fruits.
Uses of esters
Caffeine (C8H10N4O2) is an example of a class of compounds
called alkaloids which are produced by plants.
The name alkaloid means “alkali-like”, where alkali is a base
and hence refers to
these basic properties.
Carryout the experiment to extract caffeine from tea.
Uses of esters
Caffeine is more soluble in the
organic solvent ethyl ethanoate
than in water, so we will
extract caffeine into the
organic solvent to separate it
from glucose, tannins, and
other water soluble compounds
using a separating funnel.
.
The ethyl ethanoate portions
can be combined and the ethyl
ethanoate
removed
by
evaporation to leave the
caffeine
c) Hydrolysis of Esters
Learning intention
Learn how esters can be broken
down by hydrolysis into the parent
carboxylic acid and alcohol.
Hydrolysing Esters
Condensation
Alcohol + Carboxylic Acid  Ester + Water
Hydrolysis
Alcohol + Carboxylic Acid  Ester + Water
The ester is split up by the chemical action of water, hydrolysis.
The hydrolysis and formation of an ester is a reversible reaction.
O
R C
O
R
+
H
Bonds broken
Ester + Water
+
O
O
H
R C
O
O
R
H
H
Bonds formed
Carboxylic Acid + Alcohol
http://www.educationscotland.gov.uk/highersciences/c
hemistry/consumerchemistry/fruitflavours/makingest
ers.asp
Percentage yields
CH3COOH + CH3CH2CH2OH <=> CH3COOCH2CH2CH3 + H2O
4.3 g of propyl ethanoate was produced when 6 g of ethanoic
acid was reacted with propan-1-ol.
What is the percentage yield of the ester?
Percentage yield = actual yield/theoretical yield x 100%
Fats and oils
Overview
In this section, study the chemistry
and structure of edible fats and
oils, and learn how the difference
in melting points of fats and oils
can be explained in terms of
structural differences.
a) Edible fats and oils
Learning intention
Learn about the characteristic
properties of fats and oils and
study how they are formed by a
condensation reaction of glycerol
with fatty acids.
Fats in the Diet
Fats provide more energy per gram than carbohydrates.
Fat molecules are insoluble, and tend to group together and form
a large droplet. This is how fat is stored in the adipose tissue.
We store our extra energy as fat.
The type of fat we eat is important. Animal fats contain important fat
soluble vitamins. Oils, are thought to be healthier than solid fats, as
they are less likely to be deposited inside our arteries.
However, there is an ongoing debate about which fats are better for us.
Polyunsaturated fats are considered to be less potentially harmful to the
heart.
Fats and oils
Naturally occuring
Animal fat
Vegetable oil
Marine oil
lard
suet
sunflower oil
coconut oil
cod liver oil
whale oil
Fats and Oils
50% of your
brain is fat.
Fats and oils are a range of substances all based on glycerol,
propane-1,2,3-triol.
Natural fats and oils are a mixture of triglyceride compounds.
Each OH group can combine chemically with one carboxylic acid
Molecule. The resulting molecules are fats and oils.
They are described as triglycerides.
H
H
C
O
H
H
C
O
H
H
C
O
H
The hydrocarbon chain in each can be from 4 to 24 C’s long.
The C’s can be single bonded (saturated) or double bonded
(unsaturated).
H
Glycerol
propane-1,2,3-triol
a trihydric acid
Fats and oils
Fats and oils are built from an alcohol with three -O-H groups.
glycerol
Systematic name is propane-1,2,3-triol
Fatty Acids
C17H35COOH
H 3C
CH 2
CH 2
C17H33COOH
H 3C
CH 2
CH 2
CH 2
Stearic Acid (suet, animal fat) Saturated
CH3(CH2)16COOH
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH3(CH2)7CH=CH(CH2)7COOH
CH 2
CH 2
CH 2
CH
CH 2
Humans fatty acids
Oleic acid
47%
Palmitic acid
24%
Linoleic acid
10%
Stearic acid
8%
CH
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
O
C
OH
Oleic Acid (olive oil) Unsaturated
CH 2
O
CH 2
C
OH
Octadec-9-enoic acid
Fats and oils
The other components of fat molecules are carboxylic acids
such as
Stearic acid
Systematic name is octadecanoic acid
Fats and oils
Fats and oils are ESTERS of glycerol and
long chain carboxylic acids
Fats and oils
Removal of water in the condensation reaction gives -
The molecular formula shown above suggests that the fat
molecule is shaped like an E, but the molecule is actually
shaped more like this:
b) The melting point of
fats and oils
Learning intention
Learn how differences in structure
of fats and oils lead to differences
in strength of intermolecular
forces,
and
therefore
to
differences in melting points.
.
Fats and oils
Fats are mainly built from carboxylic acids with
C-C single bonds.
Stearic acid in beef fat
Oils have some C=C bonds in the carboxylic acids
from which they are made.
Oleic acid in olive oil
Fats and oils
Oil
Double bonds in oil make the molecule less compact.
Less tightly packed molecules make oils liquid.
Fat
Fat molecules pack together more tightly,
making fats solid at room temperature.
Fat
Oil
Fat molecules pack together
tightly, making fats solid at
room temperature.
Double bonds in oil make
the molecule less compact.
Less tightly packed molecules make oils
liquid because the bonds between molecules
are weaker.
Hydrogenation
The addition of hydrogen to an unsaturated
oil will ‘harden’ the oil. Increase it’s m.p.
The hydrogen is added across the double bond.
Used with margarine, otherwise margarine
would be a liquid when taken out of the fridge.
http://www.educationscotland.gov.uk/highersci
ences/chemistry/animations/oilsfats.asp
Unsaturation in fats and oils
1. Using a plastic pipette, add five drops of olive oil to 5 cm3 of
hexane in a conical flask.
2. Use a burette filled with a dilute solution of bromine water
(0.02 mol dm–3) (Harmful and irritant). Read the burette.
Unsaturation in fats and oils
3. Run the bromine water slowly into the oil solution. Shake vigorously
after each addition. The yellow colour of bromine disappears as
bromine reacts with the oil. Continue adding bromine water to
produce a permanent yellow colour.
4. Read the burette. Subtract to find the volume of bromine water
needed in the titration.
5. Repeat the experiment with: five drops of cooking oil (vegetable)
and five drops of cooking oil (animal).
Fats and Oils
The degree of saturation in a fat or oil can be determined by the
Iodine Number. (bromine can also be used).
The iodine reacts with the C=C bonds, so the greater the iodine
number, the greater the number of double bonds.
Fat
Av Iodine
No
Butter
40
Beef Fat
45
Lard
50
Olive Oil
80
Peanut Oil
100
Soya Bean
Oil
180
Solid fats – butter, beef fat & lard have low
iodine numbers because they are more
saturated than the unsaturated oils.
Margarine is made from vegetable oils, butter
from animal fats. One reason why margarine
spreads better!
Omega 3 fatty acids make up a large % of
your brain’s fat.
In practice both fats and oils are mixtures of esters
containing both saturated and unsaturated compounds.
Beef Fat
Olive oil
In general oils have a higher proportion of unsaturated
molecules.
Structures of Fats and Oils
Hydrolysis of a fat or oil produces a molecule of glycerol (alcohol) for
every 3 carboxylic acid molecules. The carboxylic acids are usually called
long chain fatty acids. Most fats and oils are, in fact, esters of
propane-1,2,3-triol, sometimes called, triesters.
H
H
C
O
O
C
R1
R 1,R 2,R 3 are long carbon chains,
which can be the same or different
O
H
C
O
C
R2
O
H
C
O
C
R
3
H
Glycerol
part
Fatty acid part
Triesters.
Hydrolysis
Glycerol + Fatty Acids
Proteins
Overview
In this section, study the structure
and function of proteins. Learn
about how they are formed from
amino acids in condensation
reactions, and how they are
broken down by hydrolysis.
a) Function of proteins
Learning intention
Learn about the function
proteins in living things.
of
Proteins
• Introduction to proteins
An animation of three proteins which demonstrate
common structural elements despite their very
different functions.
Protein Structures
Some proteins are composed of a single polypeptide chain, but many consist
of two or more polypeptide chains.
Proteins are classified according to their shape into fibrous and globular
proteins.
Fibrous proteins
These have their polypeptide chains interwoven. The polypeptide chains are
held together by hydrogen bonding, between the N-H and the C=O groups.
This gives these proteins their properties of toughness, insolubility, and
resistance to change in pH and temperature. So they are found in skin,tissue,
(collagens), hair, nails (keratins).
Globular proteins
Proteins which operate within cells need to be soluble. The polypeptide chains
are coiled together in spherical shapes. E.g. Haemoglobin and many hormones.
e.g. Insulin, was the first protein structure to be worked out.
Enzymes are globular proteins.
Protein Structures
Silk is a typical example of a fibrous protein.
Silk
This view shows the
protein chains contain 2
different amino acids.
This view shows
the individual
atoms in the
protein chains.
Protein Structures
Albumen, in egg white, is a globular protein..
Albumen
backbone view
atom view
Protein Structures
Enzymes are globular proteins. The structure of amylase is
shown below.
Starch molecule in the enzyme’s active site.
Enzyme Activity
Enzymes catalyse chemical reactions in the body. Each
enzyme has a unique shape held together by many weak
bonds. Changes to pH and temperature can denature the
enzyme. This changes the enzymes shape stops it working
properly.
Narrow optimum range
Enzyme
activity
Temp or pH
The bonds that hold most biological enzymes
are broken around 60oC.
Enzyme Activity, Lock and Key
The critical part of an enzyme molecule is called its active
site.
This is where binding of the substrate to enzyme occurs and
where catalysis takes place.
Most enzymes have one active site per molecule.
Substrate
Enzyme
Enzyme Activity, Lock and Key
Substrate
Enzyme
Active site
Enzyme Activity, Lock and Key
The substrate becomes activated
Enzyme
Enzyme Activity, Lock and Key
The substrate becomes activated
Enzyme
Enzyme Activity, Lock and Key
The complex molecule splits
Enzyme
Enzyme Activity, Lock and Key
The complex molecule splits
Enzyme
b) Amino Acids
Learning intention
Learn about the characteristic
chemistry of amino acids, the
building blocks of proteins.
Amino acids
All proteins contain the elements C,O,H, N. They are condensation polymers,
made by amino acids linking together.
The body cannot make every type of amino acids that it needs.
So our diet must contain essential amino acids. (about 10 of them).
We synthesis the others.
Amino Acids
H R
O
H N C
C
R
O H
NH2CHCOOH
Most proteins contain
20+ different amino
acids
H
When R is Hydrogen, the amino acid is glycine (Gly) (aminoethanoic acid)
When R is CH3, the amino acid is alanine (Ala) (2-aminopropanoic acid)
Amino acids
http://www.educationscotland.gov.u
k/highersciences/chemistry/animati
ons/chemicalequations.asp
This animation illustrates the
process of protein formation
by the condensation of the
carboxylic acid and amine
groups of amino acids. It also
looks at the reverse process
of protein hydrolysis
c) Amide links
Learning intention
Learn how proteins are formed by
condensation reactions of amino
acids to produce amide (peptide)
links.
Protein Polymers
Proteins are condensation polymers, made by amino
acids linking together. An amine group of one
molecule links to the carboxyl group of another
molecule to form an amide link or peptide bond.
Protein Polymers
CH3
H
H
O
N–C-C
OH
H
H
+
CH3
H
O
N–C-C
OH
H
H
+
glycine
alanine
H
N–C-C
H
O
OH
H
alanine
Tripeptide, ala-gly-ala
CH3 O
H H O
H CH3
H
O
N–C– C - N–C–C- N–C-C
OH
H
H
H
H
Polypeptide chain can have
10000
amino acids
amide (peptide) link
+ 2H2O
d) Hydrolysis of protein
Learning intention
Learn how proteins are broken
down to amino acids by the
process of hydrolysis.
Protein hydrolysis
Proteins are broken down during digestion.
Digestion involves the hydrolysis of proteins to form amino acids
Protein
+ 2H2O
Amino
acids
Identifying amino acids by
chromatography
In the lab a protein can be
hydrolysed back to its constituent
amino acids by refluxing with
concentrated hydrochloric acid for
several hours.
Amino acids can be identified by
the use of paper (or thin layer)
chromatography.
A piece of chromatography paper
is spotted with some amino acids
suspected as being present and
also with the hydrolysed protein.
Identifying amino acids by chromatography
By comparing the position of
the spots of the known amino
acids with that of the
hydrolysed protein, the amino
acids in the protein can be
identified.
•Add your results to the
diagram
•The hydrolysed fruit juice
contained?
Chemistry of cooking
Overview
In this section, learn how
functional groups in volatile
molecules influence food flavour,
and find out how cooking affects
the structure of protein in food.
a) Flavour in food
Learning intention
Learn how the chemistry of certain
functional groups in volatile
molecules in foods influence
flavour.
The chemistry of flavour
The chemistry of flavour
Molecules responsible for flavour in vegetables are normally trapped
inside the cell walls. During cooking the cell walls are damaged for two
reasons:
• Chemical damage occurs as the cell walls, which are made of cellulose,
break down.
• Physical damage occurs as water inside the cells boils forming steam
and the cell walls break open.
The chemistry of flavour
A major issue in cooking is to retain molecules responsible for flavour in the food –
overcooking can result in loss of these molecules. One destination for lost flavour
molecules is in the cooking water. This will occur if the flavour molecules are watersoluble. If this is the case, many of the flavour molecules will be lost down the drain when
the cooking water is poured away.
The chemistry of flavour
• What is flavour? Illustrates the idea that flavour is taste
plus aroma, and shows tasting experiments in which a
blindfolded taster holds his nose and becomes unable to
identify flavour.
• Chocolat coulant Heston Blumenthal describes how to
make a pudding containing chocolate and cheese and
explains why this unlikely-sounding combination tastes
good.
• Fire and spice: the molecular basis for flavor Explains the
stereochemical theory of odour which suggests that a
molecule that fits into an olfactory receptor can fire nerve
cells, ultimately producing a particular odour perception
b) Flavour in food
Learning intention
Learn how heating proteincontaining foodstuffs leads to a
change in food texture as
intermolecular forces are broken.
Changes in protein structure on
heating
• Within proteins, the long chain molecules may be twisted
to form spirals, folded into sheets, or wound around to
form other complex shapes. The chains are held in these
forms by intermolecular bonding between the side chains
of the constituent amino acids. When proteins are heated,
during cooking, these intermolecular bonds are broken
allowing the proteins to change shape (denature).These
changes alter the texture of foods.
• Cooking meat Experiments in which different cuts of meat
are cooked under different conditions to determine the
optimum cooking temperature.
Oxidation of foods
Overview
In this section, learn how oxidation
reactions
in
foods
convert
alcohols
to
aldehydes
and
ketones, and study the role of
antioxidants in the preservation of
foods.
a) Oxidation of alcohols
Learning intention
In this section, learn about the
products of oxidation of primary,
secondary and tertiary alcohols.
Find out about important mild
oxidising agents and learn how to
spot an oxidation reaction in a
carbon compound.
Classification of alcohols
H
H
H
C
C
H
OH
CH3
H
H
C
CH3
O
H
H3C C
CH3
H
H
H
H
C
C
C
H
OH
H
propan-2-ol
H
CH3
Secondary alcohol,
TWO C’s joined to the
C bonded to
the OH group
Primary alcohol,
ONE C joined to the
C bonded to
the OH group
O
Tertiary alcohol,
THREE C’s joined to
the C bonded to
the OH group
CH3
H
H3C
C
CH3
OH
2-methylpropan-2-ol
Oxidation of Alcohols
Primary alcohols can be oxidised by a number of oxidising agents, in two
stages, 1st Stage - Hydrogen is lost; 2nd Stage - oxygen is gained.
When applied to carbon compounds, oxidation results in an increase in
the oxygen to hydrogen ratio.
1st
H
R
C
O
oxidation
H
+
O
R
O
R
C
H
+
H2O
aldehyde
O H
2nd
C
H
aldehyde
+
O
oxidation
O
R
C
O
H
Carboxylic acid
Secondary alcohols can be oxidised to form ketones,
Tertiary alcohols do not undergo oxidation.
O
R
C
ketone
R1
b) Aldehydes and ketones
Learning intention
Learn about the characteristic
functional groups and chemical
reactions of aldehydes and
ketones. Study how aldehydes
and ketones are named and
drawn.
Aldehydes and Ketones
H
+ C=O
Methanal, 40% in water is formalin,
and is used to make polymers
C=O
Ethanal, It’s trimer (CH3CHO)3 is used as a
sleep inducing drug. It also causes a hangover
C=O
Butanone, is a solvent used to make VHS tapes.
H
CH3
H
CH3CH2
CH3
CH3
CH3
Butan-2-one
C=O
C4H8O
Propanone, nail varnish remover and
is used in the making of perspex
Aldehydes and Ketones
Distinguishing tests
(Using mild oxidising agents.)
Aldehydes are oxidised to carboxylic acids
Ketones do not react with mild oxidising agents
1. Fehlings solution contains Cu2+ ions (blue) which form Cu+ ion
(orange-red) in the presence of aldehydes.
2. Tollen’s reagent contains Ag+ ions, which form Ag in the presence
of aldehydes (silver mirror test)
3. Acidified Potassium Dichromate orange Cr2O72-(aq) to green Cr3(aq)
Oxidation
INTRODUCTION
Both aldehydes and ketones contain the carbonyl group.
C
O
In aldehydes a hydrogen atom is bonded to the carbonyl group but in
ketones the carbonyl group is always flanked by carbon atoms:
O
C
aldehyde
O
H
C
C
C
ketone
This structural difference accounts for the fact that aldehydes can
undergo mild oxidation to form carboxylic acids but ketones resist
oxidation. Oxidising agents can therefore be used to distinguish between
aldehydes and ketones.
The aim of this experiment is to use the mild oxidising agents, acidified
potassium dichromate solution, Benedict's solution and Tollens' reagent, to
distinguish between two given carbonyl compounds one of which is an
aldehyde and the other a ketone.
Oxidation
Procedure
1. Before collecting the carbonyl compounds X and Y set up a water bath and heat
the water until it boils. Turn off the Bunsen.
2. Add sulphuric acid to each of two test tubes to a depth of about 2 cm. Then add
potassium dichromate solution to both to give a total depth of about 3 cm in each.
3. To one of these test tubes add about 5 drops of compound X and to the other
add about 5 drops of compound Y.
4.Place both test tubes in the water bath and observe and record any changes.
5.Add Benedict's solution to each of two test tubes to a depth of about 3 cm.
6. Repeat steps 3 and 4.
7. Add Tollens' reagent to each of two very clean test tubes to a depth of about 3
cm.
8. Repeat steps 3 and 4 and immediately after, wash the contents of the test
tubes down the drain with large amounts of water.
Introducing alcohol
This page explains what alcohols are, and what the
difference is between primary, secondary and tertiary
alcohols.
Naming alcohols, aldehydes and ketones
Information from BBC Bitesize on the rules for naming
organic compounds.
c) Antioxidants
Learning intention
Learn about the chemistry of the
antioxidant
molecules
which
prevent oxidation reactions in
foods from taking place.
Oxidation of food
• Oxidation reactions can occur when food is exposed to
oxygen in the air.
• Foods containing fats or oils are at the greatest risk of
oxidation.
Foods rich in fats and oils
Oxidation of Fats
Fats and oils, or foods containing them, are the most likely to have problems
with oxidation. Fats react with oxygen and even if a food has a very low fat
content it may still need the addition of an antioxidant. They are commonly used
in:
•vegetable oil
•snacks (extruded)
•animal fat
•meat, fish, poultry
•margarine
•dairy products
•mayonnaise / salad dressing
•baked products
•potato products (instant mashed potato)
http://www.understandingfoodadditives.org
Effects of oxidation on food
When fats react with oxygen they are broken down,
causing:
– deterioration of flavour (rancidity)
– loss of colour
– loss of nutritional value
– a health risk from toxic oxidation products.
As the fat decomposes and reacts with oxygen, chemicals called
peroxides are produced. These change into the substances
characteristic of the smell and soapy flavour of a rancid fat.
Antioxidants prevent the formation of peroxides and so slow the
process of the food 'going off'. Some antioxidants react with
oxygen itself and so prevent the formation of peroxides.
Air-tight packaging, using inert gases like nitrogen, vacuum
packing and refrigeration can all be used to delay the oxidation
process. However, these can still be inefficient and adding
antioxidants can be an effective way of extending the shelf life of a
product.
http://www.understandingfoodadditives.org
Fat breaking down
Fat
Oxygen
Fat molecules
CH3
CH2
CH2
CH2
CH2
CH2
CH2
C
O
O
H
Fat
O
C
H
O
C
H
C
H
H
C
CH2
CH2
CH2
O
O
CH2
C
CH2
CH2
CH2
CH2
CH3
CH2
CH2
CH
CH
CH3
R
CH2CH2CH2CH CH CH3
Radicals attack near the double bond
(NB ‘R’ represents the remainder of
the fat molecule)
Antioxidants
• Antioxidants are chemicals that are added to food to
prevent the food from ‘going off’.
• An antioxidant is a substance that slows down or
prevents the oxidation of another chemical.
Oxidative damage
• Oxidation reactions can produce free radicals.
• A free radical is a highly reactive species containing an
unpaired electron.
• Free radicals can damage food by removal of an
electron.
• Antioxidant molecules ‘mop up’ free radicals to protect
the foodstuff.
Radical now in a stable pair
Damaging free radical
Neutralised free
radical
Electron
transferred
Antioxidant
Antioxidant
converted to a
stable free radical
How does an antioxidant cancel out
a free radical?



The antioxidant molecule donates an electron to
the potentially damaging free radical.
A stable electron pair is formed, stabilising the
free radical.
The antioxidant itself becomes oxidised (loses an
electron).
The table shows some typical antioxidants:
Antioxidant
E-number
Typical foods
Ascorbic acid (vitamin
C)
E300
Beers, cut fruits, jams, dried potato. Helps to prevent cut and pulped foods from going brown
by preventing oxidation reactions that cause the discolouration. Can be added to foods, such
as potato, to replace vitamin C lost in processing.
Tocopherols
E306
Oils, meat pies. Obtained from soya beans and maize. Reduces oxidation of fatty acids and
some vitamins.
Butylated
hydroxyanisole (BHA)
E320
Oils, margarine, cheese, crisps. Helps to prevent the reactions that break down fats and cause
the food to go rancid .
E330
Jam, tinned fruit, biscuits, alcoholic drinks, cheese, dried soup. Naturally-occuring in citrus
fruits like lemons. Helps to increase the anti-oxidant effects of other substances. Helps to
reduce the reactions that can discolour fruits. May also be used to regulate pH in jams and
jellies.
Citric acid
http://www.understandingfoodadditives.org
Antioxidants in action
Oxidation
occurs when
the apple is
left exposed
to air
The apple is
protected
when dipped in
orange juice
containing the
antioxidant
vitamin C
Antioxidants
Oxidation reactions happen when chemicals in the
food are exposed to oxygen in the air. In natural
conditions, animal and plant tissues contain their own
antioxidants but in foods, these natural systems break
down and oxidation is bound to follow.
Oxidation of food is a destructive process, causing
loss of nutritional value and changes in chemical
composition. Oxidation of fats and oils leads to
rancidity and, in fruits such as apples, it can result in
the formation of compounds which discolour the fruit.
Antioxidants are added to food to slow the rate of
oxidation and, if used properly, they can extend the
shelf life of the food in which they have been used.
http://www.understandingfoodadditives.org
Vitamin C (ascorbic acid)
• The antioxidant vitamin C can act as a reducing agent
(electron donor), preventing oxidation (electron loss)
from the foodstuff.
C6H8O6
Ascorbic
acid
C6H6O6 + 2H+ + 2eDehydroascorbic acid
Antioxidants and health
benefits
There may be health benefits from the use of antioxidants.
Oxidation reactions in the body could be linked to the build-up
of fatty deposits that cause blockages in arteries that can cause
heart attacks. Antioxidants may be important in preventing this
and there could also be a link with the prevention of certain
cancers, arthritis and other conditions. The picture is not yet
clear and a great deal of research needs to be undertaken.
http://www.understandingfoodadditives.org
Do antioxidants help us live
longer?
Studies involving 230.000 men and women across the UK have
shown that there is no convincing proof that antioxidants have any
effect on how long people can live. However 40% of women and
30% of men are reportedly taking these supplements and spending
over £333 million on them per year.
Impact of antioxidants on
health
Free radicals in living cells
Free radicals are present in all living cell and are a part of the cell
processes. However excessive free radicals in our cells can attack the
cell membranes (the outer coat of the cell). This attack causes cell and
tissue damage.
Radicals can also break strands of DNA (the genetic material in the cell).
Some of the chemicals known to cause cancer, do so by forming free
radicals.
The imbalance between free radicals and antioxidants can lead to
disease and ill health. The 4 main non-enzymatic antioxidants melatonin,
α-tocopherol (Vitamin E), ascorbic acid (Vitamin C) and β-carotene
(precursor for Vitamin A) can be found in a range of foods in our diet.
However medical opinions are divided as regards the impact these
antioxidants have our on general health.
Melatonin
This is a hormone which helps to regulate sleep in our bodies.
This compound can be termed as a terminal or suicidal
antioxidant as once it has removed the free radicals it has to
be replaced.
H 3C
O
HN
HN
CH3
O
α-tocopherol
This is a form of vitamin E and can be found in vegetable oil,
nuts and seeds. It has been suggested that it is good for the
skin.
CH3
HO
H
H 3C
H
CH3
CH3
CH3
O
CH3
CH3
CH3
Ascorbic Acid
This is also known as Vitamin C and is commonly found in fruits and
vegetables. It is one of the essential vitamins and the human body is
unable to synthesize it. It can be easily oxidised and acts as a hydroxyl
or superoxide anion radical scavenger.
HO
H
O
HO
HO
O
OH
β-carotene
This is a precursor to vitamin A. It is a highly red-orange pigment found in
plants and fruits. In particular it gives carrots their orange colour. It
helps human cells to absorb vitamin A.
H 3C
H 3C
CH3
CH3
CH3
CH3
CH3
CH3
H 3C
CH3
Soaps and Emulsions
Overview
In this section, learn about the
chemistry of soap-making, find
about how soaps and detergents
clean, and study the chemistry of
emulsions and emulsifiers.
a) Making soap
Learning intention
Find out how soaps are formed by
alkaline hydrolysis of fats and oils.
Soaps
Soaps are salts of fatty acids.
Alkaline hydrolysis is used to make sodium salts of fatty acids Soaps
are formed by the alkaline hydrolysis of fats and oils by sodium or
potassium hydroxide by boiling under reflux conditions:
.
H
H
C
O
O
C
C
O
H
C
O
C
C
O
H
C
O
C
C
17
17
17
H
H
H
H
35
35
35
H
Glyceryl tristearate
+ 3NaOH
H
C
O
H
H
C
O
H
H
C
O
H
H
Glycerol
+ 3 C 17 H 3 5 CO O -- Na +
Sodium stearate
(soap)
Soap formation
This animation describes the formation of
soap by the alkaline hydrolysis of fats / oils
followed by neutralisation to form sodium
salts of fatty acids.
The structure
of soap
Hydrophobic
tail
COO- Na
+
Hydrophilic
head
The long covalent hydrocarbon chain gives rise to the hydrophobic (water hating)
and oil-soluble (non-polar) properties of the soap molecule (represented in yellow).
The charged carboxylate group (represented in blue) is attracted to water
molecules (hydrophilic). In this way, soaps are composed of a hydrophilic head and a
hydrophobic tail:
b) Cleansing action of
soap
Learning intention
Learn how the characteristic
structure of soap and detergent
molecules
allows
effective
cleaning of oily stains to take
place.
Cleansing action of soaps
The following ball (blue for hydrophilic head group) and stick (yellow
for hydrophobic tail group) diagram represents the initial interaction
of soap on addition to water and material with a grease stain:
When the solution containing soap and water is agitated (stirred
vigorously) the interactions of hydrophobicity and hydrophilicity
become apparent. The hydrophobic, non-polar, tails burrow into the
greasy, non-polar molecule – like attracting like. In the same way
the polar hydrophilic head groups are attracted to polar water
molecules. The head groups all point up into the water at the top of
the grease stain.
The attraction of the head group to the surrounding water,
via polar-to-polar interactions, is so strong that it causes
mechanical lift of the grease molecule away from the material
on which it was deposited. The hydrophobic tails are anchored
into the grease due to non-polar to non-polar attraction. In
combination, these effects allow for the removal of the
grease stain.
http://www.educationscotland.
gov.uk/highersciences/chemis
try/animations/cleansingsoap.a
sp
c) Emulsions in food
Learning intention
Learn about the characteristics of
an emulsion, and study the
chemistry of typical emulsifier
molecules.
Emulsifier molecules
An emulsion contains small droplets of one liquid dispersed in an another
liquid.
Emulsions in food are mixtures of oil and water.
To prevent oil and water components separating into layers, a soap-like
molecule known as an emulsifier is added.
Emulsifiers for use in food are commonly made by reacting edible oils with
glycerol to form molecules in which either one or two fatty acid groups are
linked to a glycerol backbone rather than the three normally found in edible
oils. The one or two hydroxyl groups present in these molecules are
hydrophilic whilst the fatty acid chains are hydrophobic.
The presence of this emulsifier is shown on packaging by E-numbers, E471 and is
one of the most common on food packaging.
Emulsifiers
Mayonnaise contains oil and water. The emulsifier
keeps these mixed and without it the oil and water
separate.
Emulsifiers in food
Emulsifiers in food
Emulsifiers are among the most frequently used
types of food additives. They are used for many
reasons.
Emulsifiers can help to make a food appealing. They
are used to aid in the processing of foods and also
to help maintain quality and freshness.
In low fat spreads, emulsifiers can help to prevent
the growth of moulds which would happen if the oil
and fat separated.
Emulsifiers in food
Foods that Commonly Contain Emulsifiers
Biscuits
Toffees
Bread
Extruded snacks
Chewing gum
Margarine / low fat
spreads
Breakfast cereals
Frozen desserts
Coffee whiteners
Cakes
Ice-cream
Topping powders
Desserts / mousses
Dried potato
Peanut butter
Soft drinks
Chocolate coatings
Caramels
http://www.educationscotland.gov.uk/higherscienc
es/chemistry/animations/emulsions.asp
This animation explains the difference
between a stable and an unstable emulsion,
and goes on to show how addition of an
emulsifier can stabilise an emulsion which
is otherwise unstable. The chemical
structure of a typical emulsifier is described
and this is used to explain the favourable
properties of emulsifiers
Fragrances
Overview
In this section, learn about the
chemistry
of
terpenes
and
essential oils, key components of
fragrances.
a) Essential oils
Learning intention
Learn about the constitution,
properties and uses of essential
oils.
Essential oils
• Essential oils are the concentrated extracts of
volatile, non-water-soluble aroma compounds
from plants.
• Essential oils are widely used in perfumes,
cosmetic products, cleaning products and as
flavourings in foods.
Essential oils
• Essential oils are mixtures of organic
compounds.
• Terpenes are the key components in most
essential oils.
The history of essential oils
• The benefits of essential oils have been
recognised for thousands of years.
• Their use is described in the New Testament
of the Bible.
• They were used in anointing rituals and in
healing the sick.
The history of essential oils


The ancient Egyptians used essential
oils for embalming, religious rites and
medicinal purposes.
King Tut’s tomb was found to contain 50
jars of essential oil when it was opened
in 1922.
Modern uses
Cosmetics
Cleaning
Flavours
Dentistry
Essential oils
Adhesives
Perfumes
Insect
repellents
Medical
What are essential oils?
• ‘Essential’ refers to the fact that the oil carries the
distinctive essence (scent) of the plant.
• Concentrated, volatile, non-water soluble aroma
compounds extracted from plants.
• Contain no artificial substances, unlike perfumes and
fragrance oils.
Essential oils – composition
• Essential oils are mixtures of organic compounds.
• Terpenes are the key components of all essential oils.
Essential oils – chemistry
• The distinctive character of an essential oil can be
attributed to the functional group present in its key
molecule.
• Esters, aldehydes, ketones and alcohols are all found
in essential oils.
Essential oils – perfume
• The ester linalyl acetate is found in the essential oil
lavender.
• This ester is often added to perfumes.
H3C
C
C H3
O
C
H3C
C H2
CH
O
C H3
C
C H2
Linalyl acetate
C H2
CH
Essential oils – cleaning
• The essential oil known as lemon oil contains the terpene
d-limonene.
• It is known for its ability to act as a natural solvent and a
cleanser.
H3C
C H2
C
CH
H2C
C H2
H2C
CH
C
C H3
L im o n e n e
(s k in o f c itru s fru its )
Hospital cleaners
• Certain essential oils kill bacteria and fungi (including
MRSA and E. coli) within 2 minutes of contact.
• Essential oils are blended into soaps and shampoos used
in hospitals to eradicate deadly ‘super bugs’.
Essential oils – cosmetics
• The essential oil geraniol is added to some cosmetics to
balance and revitalise the skin.
C H3
C H3
C
H3C
C
C H2
CH
C H2
G e ra n io l
C H2
CH
OH
Essential oil – cold sores
• Melissa oil contains the terpene citral,
which is used to combat cold sores.
CH3
C H2
C
H3C
CH
C H2
C itra l
C H3
H
C
C
CH
O
Essential oils – toothpaste
• The essential oil thymol has antiseptic properties.
C H3
C
HC
CH
C
CH
HO
C
CH
H3C
T hym ol
CH3
Steam distillation
• Steam distillation is one of the methods used to
extract essential oils from plants.
• Steam passes over the plant and extracts the essential
oil.
• The mixture evaporates and passes into the
condenser.
• The essential oil vapour is chilled and collected.
Steam distillation
Essential oils – summary
• Concentrated extracts of volatile, non-water-soluble
aroma compounds from plants.
• Widely used in perfumes, cosmetics, cleaning
products and flavourings.
• Mixtures of organic compounds.
• Terpenes are the key components of most essential
oils.
b) Terpenes
Learning intention
Learn about the chemistry and
uses of terpenes, a key group of
unsaturated molecules based
upon isoprene.
Terpenes
• The name ‘terpene’ is derived from the
Greek word ‘terebinth’.
• Terebinth is a type of pine tree from
which terpene-containing resins are
obtained.
What are terpenes?
• Natural organic compounds.
• Components of a variety of fruit and floral
flavours and aromas.
• Used in perfumes, essential oils and
medicines.
Essential oils contain terpenes
• Lavender – used to relieve tension.
• Ylang-ylang – used to treat anxiety.
• Lemon oil – aids good circulation.
• Essential oils often contain a mixture of
terpenes.
Spices contain terpenes
• Terpenes in plants can be oxidised to produce
the compounds responsible for the distinctive
aroma of spices.
• Terpenes containing oxygen or other functional
groups are known as ‘terpenoids’.
• Common spices containing terpenes include
cloves, cinnamon and ginger.
Terpenes are unsaturated
• Terpenes are unsaturated compounds.
• All terpenes are built up from units of
isoprene.
Isoprene
• Isoprene is the common name for
2-methylbuta-1,3-diene
C H3
H2C
C
H3C
CH
C H2
C
C H2
H2C
CH
Isoprene
Head
T a il
C H2
C H3
C
CH
=
C H2
Iso p re n e
(2 -m e th ylb u ta -1 ,3 -d ie n e )
One isoprene unit contains five carbon
atoms
Building terpenes from isoprene
Isoprene units can be linked:
• head to tail to form linear terpenes
• in rings to form cyclic terpenes.
Myrcene – a linear terpene
Head
C H 2 H CC H 2
3
C HH23 C
H3C
C
H2C
Head
Tail
C
CH
H3C
CC
CH
Tail
CH
H2
C
2
CH
H
C
HH22CC
• Myrcene is a component of plants, including
bay, ylang-ylang and thyme.
Limonene – a cyclic terpene
C H2
H3C
C
CH
H2C
C H2
H2C
CH
C
C H3
L im o n e n e
(s k in o f c itru s fru its )
Menthol – a cyclic terpenoid
C H3
H3C
CH
CH
OH
H2C
CH
H2C
C H2
CH
C H3
M e n th o l
(p e p p e rm in t)
This terpene has been
oxidised to a terpenoid
Absinthe – a cyclic terpenoid
CH3
H3C
This terpene has been
oxidised to a terpenoid
CH
C
H2C
CH2
HC
C
CH
C H3
T h u jo n e
(A b sin th e )
O
Camphor – a cyclic terpenoid
C H3
H3C
C
CH
C H2
CH2
C
H2C
H3C
C
O
Camphor
(C a m p h o r tre e )
a-Selinene – a cyclic terpene
3 isoprene units
C H3
CH2
H2C
H2C
CH
C
C H2
C
C H2
C
C H2
C H2
C
H
C H3
a -S e lin e n e
CH2
15 carbon atoms
β-carotene – a linear terpene
C H2
H3C
H3C
C
C
H2C
C
C H2
CH
C
CH
H2C
CH
C H2
C
C H2
C H3
C H3
CH3
C
CH
CH
CH
CH
C
8 isoprene units
40 carbon atoms
CH
C
C
CH
H3C
CH3
CH3
CH
CH
CH
CH
CH
C
 -ca ro te n e
C H3
C H3
Questions
• Which unit makes up every terpene?
• How many carbons are there in an isoprene
unit?
• What is the systematic name for isoprene?
• What is an oxidised terpene known as?
Answers
• Which unit makes up every terpene?
Isoprene unit
• How many carbons there are in an isoprene unit?
Five
• What is the systematic name for isoprene?
2-methylbuta-1,3-diene
• What is an oxidised terpene known as?
Terpenoid
Summary
• Terpenes are unsaturated compounds formed by
joining together isoprene units.
• Terpenes are components in a wide variety of fruit and
floral flavours and aromas.
• Terpenes can be oxidised within plants to produce the
compounds responsible for the distinctive aroma of
spices.
Skin care products
Overview
In this section, learn about the
effect of UV-light on the skin,
including the chemistry of freeradical reactions and the role of
UV-scavengers
in
skin-care
products.
a) Effect of ultra-violet
light
Learning intention
Learn how high energy UV-light
causes damage to skin by
breaking bonds in molecules.
Sun, sea, sand and ….
Ultraviolet radiation (UV)
Image of the sun taken with
ultraviolet imaging telescope
• Ultraviolet radiation is broken into three types of
wavelengths:
• UV-A: This is the longest wavelength and is not absorbed
by the ozone. It penetrates the skin deeper than UV-B.
• UV-B: Responsible for sunburns. It is partially blocked by
the ozone layer.
• UV-C: This is totally adsorbed by the earth's atmosphere;
we encounter it only from artificial radiation sources.
Ultraviolet radiation (UV)
Ultraviolet radiation (UV) is a high-energy
form of light, present in sunlight. Exposure to
UV light can result in molecules gaining
sufficient energy for bonds to be broken.
UV damage to DNA
Damage to DNA causes mutations which stop the DNA
functioning properly
The radiation excites DNA molecules in skin cells, causing
new covalent bonds to form between adjacent cytosine
bases, producing a bulge. This mutation can result in
cancerous growths, and is known as is commonly seen in
skin cancers.
Skin cancer – malignant melanoma
In the UK, 2,000 people a year die from malignant
melanoma, and the number is increasing.
Natural defence - Melanin
Melanin is a pigment that is produced when your
skin is exposed to sunlight. It absorbs the UV
radiation found in sunlight to help protect your
skin. This results in your skin becoming darker, a
tan which is a sign that it has been damaged by UV
rays.
Melanin stops you burning so easily but it does not
prevent the other harmful effects of UV
radiation, such as cancer and premature ageing.
Photo ageing
• In the skin, UV radiation causes
collagen to break down.
• The body tries to rebuild the
collegen, disorganized collagen
fibers known as solar scars can
form.
• When the skin repeats this
imperfect rebuilding process over
and over wrinkles develop.
There’s no such thing as a healthy
tan
Photoageing caused by UVA
Exposed to sun
(through car window)
TAXI Driver
Not exposed to sun
The effects of UV - ageing of skin
How to protect yourselfSunscreen
Sunscreen works by combining organic and
inorganic active ingredients.
Inorganic ingredients like zinc oxide or
titanium oxide reflect or scatter ultraviolet
(UV) radiation.
Organic ingredients adsorb UV radiation,
dissipating it as heat.
UV photography reveals sun damage
This article illustrates how dermatologists use ultraviolet
(UV) photography to show their patients how the sun has
damaged the skin.
Your health, your choices: Sunburn
NHS information on sunburn, including symptoms,
causes, treatment and prevention.
Sunblock
Guidance from the School of Medicine at the University of
California, San Francisco, on the use of sunblock to
prevent skin cancer. Lists common active ingredients of
sunblock.
UV Radiation and Children: A study of sunglass use
to prevent ocular damage from sun exposure
M. Bauer, W. Catanio, W. Fahrman, B. Godard, R. Irwin, A. Opyd
New England College of Optometry, Boston, MA
Purpose
To determine if children are wearing sunglasses regularly.
Results cont’d
Conclusions cont’d
Figure 2. The comparison of children and adult sunglass wear.
Despite the public consciousness of UV damage there has been little
public education involved in the prevention of cataracts, pterygia, or
photokerititis. The most obvious and cost effective form of
prevention is the use of sunglasses.4 Sunglasses are available in
various styles and sizes, with 100% UV protection, at low cost.
Comparative amount of sunglass use in children and
parents
Number of responses
To investigate whether or not parents are aware of the harmful
effects of UV radiation on young children's eyes.
160
140
120
100
80
60
parents
children
40
20
0
Introduction
Never
Sometimes
Always
Amount
Figure 3. Percent of children that wear sunglass in relation to
parental use.
Up to 80% of a lifetime sun exposure is obtained before the age
18. Children require special protection as they are at the highest
risk for developing ocular damage or diseases caused by
overexposure to Ultraviolet radiation from sunlight.
It is important that parents teach their children how to enjoy fun in
the sun safely. With the right precautions, the chance of developing
ocular damage can be greatly reduced. It has been proven that
simple measures, such as the use of brimmed hats and sunglasses, as
personal protection measures can effectuate up to an 18-fold
difference in ocular UV exposure.2
a. UV damage to
cornea5
b. Pterygium5
d. Skin cancer6
c. Cataract5
Figure 1. Ocular disease manifestations.
Methods
A six-item survey was composed to access parental knowledge and
awareness of the adverse effects of sunlight on the eyes. The
surveys were handed out, with permission, at an elementary school
and a pediatrician’s office in New Jersey and Rhode Island.
Different states were surveyed in order to make the results
generalizable throughout the United States. Results of the survey
were analyzed in order to determine if public education would be
beneficial to this issue. An educational pamphlet was made in order
to inform the public on the negative effects of sunlight on the eyes.
% of children that wear sunglasses
Frequency of sunglass wear in children
Acute eye damage can occur from single outings on bright days.
Photokeratitis, (solar corneal damage) is a temporary but painful
burn on the surface of the eye (cornea). This self-healing injury
typically resolves in 24 hours with no permanent damage.1
Chronic UV exposure contributes to the development of many eye
disorders: Pterygium is an abnormal growth of fibro-vascular tissue
from the corner of the eye. If severe, a pterygium can grow over
the cornea, threatening vision loss and requires surgery to be
removed; Cataract is a clouding of the normally clear, natural lens
inside the eye. The clouded lens prevents light from reaching the
retina therefore reducing vision; Skin Cancer can develop on the
eyelids and surrounding skin. Basal cell carcinomas, squamous cell
carcinomas, and malignant melanomas can all occur from chronic UV
exposure2,3 (Figure 1).
The segment of the population at greatest risk to accrue damage
from ultraviolet radiation is children from the ages of birth to
adolescence. UV absorption by the natural lens of the eye varies
throughout life. Immediately after birth, nearly all of the UV light
is transmitted by the lens. During childhood, lens transmittance
decreases, and by the age of 25, the lens absorbs UV light almost
completely.2 Regardless of the fact that an overwhelming number of
parents thought that childhood was the ideal age to start wearing
sunglasses, only 11% answered that their children always wore
sunglasses. Children’s lack of wearing sunglasses could be due to the
fact that manufactures and advertisement companies are not using
this age group as a demographic
120.0
5.8
100.0
5.6
18.8
80.0
60.0
38.9
65.3
Child Always
Child Sometimes
56.3
Child Never
40.0
55.6
20.0
28.9
25.0
0.0
Parent Always
Parent
Sometimes
Parent
Never
Parental sunglass use
Figure 4. Parental awareness of ultraviolet radiation damage to the
eye.
UV damage awareness
No
22%
Yes realistic
28%
Results
Of the 800 surveys distributed, 235 were returned and analyzed.
Parental educational background of those surveyed included college
57%, high school/GED 21%, graduate/masters 18%, and some high
school 4%. When asked if they always, sometimes, or never wore
sunglasses it was found that the majority of parents sometimes wore
sunglasses. It was also found that the majority of their children
sometimes wore sunglasses (Figure 2,3).When asked if their child
would wear sunglasses if given a pair, 76% said yes. The majority of
parents felt that childhood was the ideal age to start wearing
sunglasses, with 75% of the responses. It was found that the
majority of the people surveyed knew that UV radiation was
damaging to the eyes (figure 4). Of these parents 50% were unable
to provide a correct possible outcome. The top three incorrect
answers
were
blindness,
glaucoma,
and
sensitivity/squinting/soreness. The top three obtained correct
answers were cataract, damage to retina, and damage to cornea.
Yes false
50%
Conclusions
According to the results found in the previous section, 78% of adults
surveyed were aware that ultraviolet radiation is damaging. However,
half of them where unaware of the actual pathologies involved. The
severity of sun exposure was also greatly underestimated. Common
incorrect answers were blindness, glaucoma, watery eyes, and
wrinkles. These general trends lead to several possible conclusions.
One being that further education is a possible solution to the lack of
adequate sunglass use.
target. The most common answer
of why children would not wear sunglasses was that they found them
uncomfortable.
More research on the design of children’s
sunglasses could be beneficial to this issue.
In conclusion, there is a serious lack of education on the damaging
ocular effects of sun exposure. Moreover, there is little
preventative behavior in preventing these potentially serious
diseases. Because it is known that sunglass protection is most vital in
childhood, it is alarming to see that a majority of youth are not
protecting their eyes.
This preliminary survey showed that there is a potential need for
public health education on the adverse effect of UV radiation on the
eye and the protection methods that could possible prevent these
effects. A larger scale survey would be beneficial to determine
nation wide parental knowledge on this subject. Future research
would determine the most effective educational program. In order
to aid the education process an ocular sun safety flyer will be
distributed to optometric offices across the state of
Massachusetts.
References
1. Cronly-Dillon, J, Rosen, E. S., & Marshall, J. Hazards of light : myths & realities :
eye and skin : proceedings of the First International Symposium of the Northern
Eye Institute. University of Manchester, July 1985.
2. Friedlaender, Mitchell. Ultraviolet Radiation and the Eye. International
Ophthalmology Clinics. 2005;45:49-52
3. Parisi, Alfio V., Green, A., & Kimlin, M. G. Diffuse Solar UV Radiation and
Implications for Preventing Human Eye Damage. Photochemistry and
Photobiology. 2000;73:135-139.
4. Van Kuijk J.G.M, Frederik. Effects of Ultraviolet Light on the Eye: Role of
Protective Glasses. Environmental Health Perspectives. 1991;96:177-184
5. Ocular Image Database, New England College of Optometry Library [Internet].
[Cited 2006 Apr 26]. http://ncoimagesdb.ne-optometry.edu/ocular.asp.
6. Basal Cell Carcinoma (BCC), University of Utah John A. Moran Eye center
[Internet]. [Cited 2006 Apr 26].
http://www.insight.med.utah.edu/opatharch/lid/basal_cell_carcinoma_bcc.htm.
Acknowledgements
A special thank you to Dr. Clifford Scott and Dr. Li Deng for their
help with this public health project.
b) Free radical reactions
Learning intention
Study the chemistry of free radical
chain reactions.
Hydrogen and chlorine
When UV light breaks bonds free radicals are
formed.
Free radicals have unpaired electrons and, as a
result, are highly reactive.
Free radical chain reactions include the
following steps: initiation, propagation and
termination.
Hydrogen and chlorine
1) Initiation
U.V. light provides the energy for the homolytic
fission of halogen into reactive halogen atoms or
free radicals (atoms with an unpaired electron).
Cl2(g) → Cl.(g) + .Cl(g)
Hydrogen and chlorine
2) Propagation
In this stage, free radicals collide with other species
but the number of free radicals is maintained (hence
the term propagation).
H2(g) + .Cl → H.(g) + HCl(g)
H.(g) + Cl2(g) → HCl(g) + Cl. (g)
These reactions continue until reactants are used
up, or until free radicals are used up by collision with
each other.
Hydrogen and chlorine
3) Termination
In this stage, free radicals are used up by
collision with each other.
H.(g) + .Cl(g) → HCl(g)
H.(g) + .H(g) → H2(g)
Cl.(g) + .Cl(g) → Cl2(g)
Free radical Substitution Methane
Another free radical reaction takes place when halogen is substituted into an alkane
in the presence of UV light. This reaction is not explosive and results in the
decolourisation of bromine.
Alkanes react with bromine in the presence of U.V. light, though the reaction with
bromine is slow. The reaction can be shown as follows:
CH4(g) + Br2(g) → CH3Br(g) + HBr(g)
The presence of acid HBr in the product can be shown with moist pH paper.
However, the reaction does not end here and further substitution can occur with
hydrogen atoms progressively replaced by halogen atoms.
The slow substitution reaction follows a free radical chain reaction, initiated by U.V.
light (hν). For convenience, the reaction can be split into three stages.
Free radical Substitution Methane
1) Initiation
U.V. light provides the energy for the homolytic fission of halogen into
reactive halogen atoms or free radicals (atoms or molecular fragments with
an unpaired electron).
Br2(g) → Br.(g) + .Br(g)
Free radical Substitution Methane
2) Propagation
In this stage, free radicals collide with other species but the number of free
radicals is maintained (hence the term propagation).
CH3-H(g) + .Br → CH3.(g) + HBr(g)
CH3.(g) + Br2(g) → CH3 - Br(g) + Br. (g)
These reactions continue until reactants are used up, or until free radicals
are used up by collision with each other.
Free radical Substitution Methane
3) Termination
In this stage, free radicals are used up by collision with each other.
Br.(g) + .Br(g) → Br2(g)
CH3.(g) + .Br(g) → CH3 - Br(g)
CH3.(g) + .CH3(g) → CH3 - CH3(g)
The product of the last equation is ethane. However, to minimise the range
of possible products, an excess of the original alkane is used and the
products separated from the excess alkane by distillation.
Free radical Substitution Methane
Evidence to support this mechanism
The reaction is initiated by U.V. light and, once started, can
continue in the dark.
Other substitution products are made such as CH2Br2, CHBr3,
CBr4 together with longer alkanes (and smaller amounts of
substitution products of these alkanes.
However, these other substitution products can be minimised
by using an excess of the original alkane to try to ensure
collision of the relatively small number of free radicals
produced by sunlight quickly uses up the bromine.
c) Free-radical
scavengers
Learning intention
Learn about the chemistry of the freeradical ‘scavenger’ molecules which
are included in many skin-care
products.
Free Radical Scavengers
Many cosmetic products contain free radical scavengers.
These are molecules which can react with free radicals to form stable
molecules and prevent chain reactions.
Melatonin and Vitamin E are examples of natural free radical scavengers.
Melatonin
Free radical scavengers are also added to food products and to plastics.
As UV light can cause wrinkling of skin, some skin-care products claim to
contain chemicals which prevent wrinkling. These are claimed to be anti-aging
creams.
Free radicals remove electrons from skin cells and damage them and wrinkles
start to develop.
• Here is a banned advert. This time Nivea Visage is suggesting that the cream
could deliver permanent benefits
Do they work?
There is a range of antioxidants used in anti-wrinkle creams, and some are better at penetrating the skin
than others. The antioxidants used in skin care are derived from Vitamins A, E and C
The derivatives of Vitamins A (retinol) and E combat free radicals. Vitamin C is used in the construction of
collagen. Other antioxidants work by exfoliating the dead skin on the surface to reveal newer, youngerlooking skin underneath. Still others create a barrier to prevent moisture loss fromClaims for retinol
derivatives say it can reduce the appearance of lines and reduce skin roughness, and blotchiness. There is
some research that says retinol can increase the thickness of the epidermis. But as the molecules are
large, they can't fit though the skin unless combined with substances that make the holes in the lipid
matrix bigger.
Vitamin E is the most widely used ingredient in skin care products, used for its moisturising and
antioxidant properties.
Predicting Physical Properties
of Molecules from Functional
Groups
Learning intentions
To become familiar with identifying key
functional groups within molecules.
To be able to explain the influence of
functional groups on intermolecular forces.
To be able to predict the physical properties
of molecules from functional groups present.
Butanoic acid has a powerful, unpleasant odour. It is
found in rancid butter, Parmesan cheese and vomit.
Carboxyl group
Can you identify and name the functional group
present in butanoic acid?
Aqueous solutions of methanal are commonly used in
embalming to preserve human or animal remains.
Carbonyl group
Can you identify and name the functional group present
in methanal?
Is methanal an aldehyde or a ketone?
Aldehyde
The molecule below is found in the disinfectant Dettol,
which we instantly recognise by its distinctive smell.
Dettol (chloroxylenol) helps us fight unwanted
bacteria.
Hydroxyl
group
Can you identify and name the functional group
present in Dettol?
4-formamidobenzoic acid is used in pharmaceutical
compositions.
Carboxyl
group
Amide group
Can you identify and name two functional groups
present on the 4-formamidobenzoic acid molecule?
Cinnamon is a tasty spice used to flavour biscuits,
cakes and pies. Cinnamon also has medicinal
properties.
Carbonyl
group
Carbon-tocarbon double
bond
Can you identify and name two functional groups in
cinnamon?
Is cinnamon an aldehyde or a ketone? Aldehyde
What is the strongest type of intermolecular force of
attraction between cinnamon molecules?
(Hint: Think about the bond polarity of the functional
groups present!)
Methyl anthranilate occurs naturally in grapes and
is used as grape flavouring in drinks and chewing
gum.
Ester link
Amino group
Can you identify and name the two functional
groups present in methyl anthranilate?
Vitamin C is needed in your diet for the growth and
repair of tissues in all parts of your body.
Ester link
Carbon-tocarbon double
bond
Hydroxyl
group
Can you identify and name three different types of
functional group on the structure of vitamin C?
Which is the strongest type of intermolecular force
of attraction between molecules of vitamin C?
Is vitamin C a polar or a non-polar molecule?
Is vitamin C soluble in water or in hexane?
(Hint: Think about which functional groups are present!)
Glucose is a simple sugar that is used as an energy
source by many living organisms.
Is glucose soluble in water or in hexane? Justify your
answer with reference to the functional groups present.
2-methylpropane is a branched hydrocarbon that is
used as a refrigerant.
Is 2-methylpropane soluble in water or in hexane?
Justify your answer with reference to the structure.