Transcript Chapter 22

1
Functional Groups
2
• The various classes of compounds
are identified by the presence of
certain characteristic groups called
functional groups.
• Through the chemical reactions of
functional groups, it is possible to
create or synthesize new
substances.
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O
O
H
O
H
water
R
H
alcohol
H
O
R
R
ether
phenol
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Classification of
Alcohols
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Alcohols are classified by the number of R groups (i.e.
carbon atoms) attached to the hydroxyl carbon as shown
here.
primary (1)
secondary (2)
tertiary (3)
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Tests for Alcohols
7
Lucas Test
• Addition of
ZnCl2 in
concentrated
HCl forms a
“turbid”
solution.
Order of
reactivity is
3o > 2o >> 1o.
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•Polyhydroxy alcohols and polyols are
general terms for alcohols that have
more than one –OH group per molecule.
•Polyhydroxy compounds are very
important molecules in living cells, as
they include the carbohydrate class of
biochemicals.
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Structural Representations of Alcohols
• An alcohol such as 2-butanol can be written
in a single-line formula by enclosing the –
OH group in parentheses and placing it after
the carbon to which it is bonded.
OH
CH3CH2CHCH3 = CH3CH2CH(OH)CH3
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Application to Biochemistry
Blood sugar (glucose) contains five
alcohol groups. Using the structure of
glucose shown here, label each group
as 1°, 2°, or 3°.
O=CHCH(OH)CH(OH)CH(OH)CH(OH)CH2OH
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Application to Biochemistry
secondary
H
C
O
OH
H
OH
OH
C
C
C
C
H
OH
H
CH 2OH
primary
H
secondary
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Naming Alcohols
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IUPAC Rules for Naming Alcohols
1. Select the longest continuous chain of
carbon atoms containing the –OH group.
2. Number the carbon atoms in this chain
so that the one bearing the -OH group
has the lowest possible number.
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IUPAC Rules for Naming Alcohols
3. Form the parent alcohol name by replacing
the final –e of the corresponding alkane by
–ol. When isomers are possible, locate the
position of the –OH group by placing the
number (hyphenated) of the carbon atom to
which the –OH is bonded immediately
before the parent alcohol name.
4. Name each alkyl side chain (or other group),
and designate its position by number.
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Name CH3CH2CH2CH2OH
4 3 2 1
CH3CH2CHCH2OH
1-butanol
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Nomenclature of Alcohols
OH
CH3
H3C CH
CH3
2-propanol
(isopropyl alcohol)
OH
cyclohexanol
H3C
CH
CH2CH2OH
3-methyl-1-butanol
HO
OH
1,3-cyclohexanediol
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Physical Properties
of Alcohols
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Physical Properties of Alcohols
• The physical properties of alcohols are
related to those of both water and
alkane hydrocarbons.
• An alcohol molecule is made up of a
waterlike hydroxyl group joined to a
hydrocarbonlike alkyl group.
O
H
O
H
water
R
H
alcohol
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Boiling Points of Alcohols
• Alcohols have relatively high boiling
points.
• The boiling points of the normal alcohols
increase in a regular fashion with increasing
number of carbon atoms.
• Branched-chain alcohols have lower boiling
points than corresponding straight-chain
alcohols.
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• Alcohols containing up to three carbon
atoms are infinitely soluble in water.
• The –OH group on the alcohol
molecule is responsible for both the
water solubility and relatively high
boiling points of the low-molar-mass
alcohols.
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Hydrogen Bonding in Alcohols
H
O
H
H
R
O
R
O
H
O
H
H
R
H
O
O
O
H
O
R
H
R
H
H
water-alcohol
alcohol-alcohol
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Glucose is one of the most important
carbohydrates in biochemistry. It has six
carbons and five alcohol groups (molar
mass = 180.2 g). How would you predict
the water solubility of glucose to differ
from that of 1-hexanol?
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Effect of Hydroxyl Groups on Solubility
Note the difference in solubility of hexanol (only one –OH
group) and glucose ( five –OH groups).
CH3CH2CH2CH2CH2CH2OH
1-hexanol
(solubility = 0.6g/100g H2O)
D-glucose
(solubility = 95g/100g H2O)
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Effect of Branching on Boiling Point
A branched-chain alcohol will have a lower boiling point
than the corresponding straight-chain alcohol.
For example 2-butanol is branched and has a b.p. of
91.5 C versus 118 C for 1-butanol.
CH3CH2CH2CH2OH
2-butanol
2-butanol
(written as a1-butanol
single-line formula )
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Chemical Properties
of Alcohols
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Chemical Properties of Alcohols
•
•
•
•
Acidic and Basic Properties
Oxidation
Dehydration
Esterification (Chapter 24)
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Basic Properties
•
If an alcohol is mixed with a strong
acid, it will accept a proton (act as a
Brønsted-Lowry base) to form a
protonated alcohol or oxonium ion.
H
H3C
O
H + H2SO4
H3C
-
+ HSO4
O
H
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Acidic Properties
•
•
2 H3C
Alcohols can also act as BrønstedLowry acids.
The resulting anion in the alcohol
reaction is known as an alkoxide ion
(RO-).
H2
C
O
H + 2 Na
2 H3C
H2
C
Na+
O
+ H2 (g)
sodium ethoxide
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Oxidation
• Oxidation is the loss of hydrogen or the
gain of bonds to oxygen by the organic
reactant.
• Carbon atoms exist in progressively higher
stages of oxidation in different functional
groups.
Alkanes
Alcohols
Aldehydes
Ketones
Carboxylic
Acids
Carbon
dioxide
increasing oxidation state
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H
R
C
O
O
OH
[O]
R
C
H + H2O
aldehyde
H
o
primary (1 )
[O]
R
C
OH
carboxylic
acid
alcohol
R
R
C
O
OH
[O]
R
C
R
ketone
H
secondary (2o)
alcohol
The –OH group gives
an organic compound
the capability of
forming an aldehyde,
ketone, or carboxylic
acid.
R
R
C
OH
[O]
No reaction
R
tertiary (3o)
alcohol
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Common Oxidizing Agents
• KMnO4
• K2Cr2O7
• O2
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Dehydration
• Alcohols can be dehydrated with
sulfuric acid to form alkenes.
H
H
H
C
C
H
OH
96% H2SO4
H
H heat
H
H
C
C
H + H2O
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Dehydration
• For many alcohols, there is more than one way to
remove water. Therefore the double bond can be located
in different positions.
• The major product in such cases is the alkene in which
the C=C bond has the greatest number of alkyl
substituents on it (or the least number of hydrogens).
H
H3C
H
H
C
C
96% H2SO4
CH2
H3C
heat
H
OH
H
2-butanol
C
H
C
CH3 + H3C
2-butene
(major product)
H2
C
H
C
CH2 + H2O
1-butene
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Utility of the Hydroxyl
Functional Group
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Common Alcohols
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Preparation of Methanol
•Methanol is a common industrial solvent prepared
by the high-pressure catalytic hydrogenation of carbon
monoxide.
•The most economical nonpetroleum source of carbon
monoxide for making methanol is coal.
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Uses of Methanol
1. Conversion to formaldehyde (use in
manufacture of polymers).
2. Manufacture of other chemicals,
especially various kinds of esters
3. Denaturing ethyl alcohol
4. Industrial solvent
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Ethanol
• Large quantities of ethanol are
prepared by fermentation.
– The conversion of simple sugars to
ethanol is accomplished by yeast.
• Industrially, ethanol is made by acidcatalyzed addition of water to ethylene.
C6H12O6
yeast
H2O
2 CH3CH2OH + 2 CO2
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Uses of Ethanol
• An intermediate in the manufacture of other
chemicals such as acetaldehyde, acetic acid,
ethyl acetate, and diethyl ether.
• A solvent for many organic substances.
• A compounding ingredient for
pharmaceuticals, perfumes, flavorings, etc.
• An essential ingredient in alcoholic
beverages.
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2-Propanol (Isopropyl Alcohol)
• 2-Propanol is made from propene.
+
CH3CH=CH2 + H2O
H
CH3CH(OH)CH3
2-propanol
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Uses of 2-Propanol (Isopropyl Alcohol)
1. To manufacture other chemicals
(especially acetone).
2. As an industrial solvent.
3. As the principal ingredient in rubbing
alcohol formulations.
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Ethylene Glycol (1,2-Ethanediol)
• Industrial synthesis
Ag catalyst
2 CH2=CH2 + O2
2
200-300 C
O
+ H2O
O
H+
ethylene oxide
(oxirane)
HOCH2CH2OH
1,2-ethanediol
(ethylene glycol)
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Uses of
Ethylene Glycol (1,2-Ethanediol)
1. In the preparation of the synthetic
polyester fiber Dacron and film Mylar
2. As a major ingredient in “permanenttype” antifreeze cooling systems
3. As a solvent in the paint and plastic
industries
4. In the formulations of printing ink and ink
for ballpoint pens.
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Glycerol (1,2,3-Propanetriol)
• Glycerol (also known as glycerine) is
an important trihydroxyalcohol.
• It is obtained as a by-product of the
processing of animal and vegetable fats
to make soap and other products.
• It is synthesized commercially from
propene.
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Uses of Glycerol
• Each directly related to the three –OH groups.
1. As a raw material in the manufacture of
polymers and explosives (nitroglycerin).
2. As an emollient in cosmetics.
3. As a humectant in tobacco products.
4. As a sweetener.
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Phenols
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Phenols
• The term phenol is used for the class of
compounds that have a hydroxy group
attached to an aromatic ring.
• The parent compound is also called phenol,
C6H5OH.
OH
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Naming Phenols
• Many phenols are named as derivatives of
the parent compound, via the general
methods for naming aromatic compounds.
OH
OH
OH
Br
phenol
m-bromophenol
NH2
p-aminophenol
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Derivatives of Phenol
Compounds of phenol are the active ingredients in the
essential oils of nutmeg, thyme, cloves, and vanilla.
OH
OH
OCH3
CH=CHCH3
isoeugenol (nutmeg)
H
C
CH3
CH3
thymol (thyme)
OH
OH
CH3
OCH3
OCH3
CH2CH=CH2
eugenol (cloves)
H
C
O
vanillin (vanilla)
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Common Phenols
OH
OH
OH
NO2
Br
para-bromophenol
Cl
Cl
Cl
Cl
Cl
ortho-nitrophenol
pentachlorophenol
OH
OH
OH
OH
CH3
meta-cresol
resorcinol
beta-naphthol
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Common Phenols/Alcohols
Cl
Cl
OH
Cl
Cl
HO
Cl
CH2
Cl
ortho-phenylphenol (Lysol)
C
OH
C
OH
3,3',5,5',6,6'-hexachlorodiphenylmethane
(hexachlorophene)
C
C
C
C
C
C
C
C
C
C
OH
trailmarker for termites
HO
CH2CH2CH2CH2CH2CH3
n-hexylresorcinol (sucrets)
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Common Phenols/Alcohols
C
H
C
C
C
OH
Cl
C
C
sex pheromone for
male Boll Weevil
C
OH
OH
Cl
C
C
C
C
C
OH
C
C
C
C
C
sex attractant for
lonestar tick
C
C
aggregating pheromone
for Bark Beetle
C
C
sex pheromone for Bark Beetle
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Common Phenols
OH
OH
(CH2)7
CH
CH
(CH2)5
CH3
oil of Poison Ivy
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Herbicides produced by Phenols
Cl
Cl
Cl
O
O
C
C
OH
2,4-dichlorophenoxy acetic acid
(2,4-D)
Cl
O
O
Cl
C
C
OH
2,4,5-trichlorophenoxy acetic acid
(2,4,5-T)
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Properties of Phenols
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Properties of Phenols
• Colorless, crystalline solid, mp = 41 °C
• Highly poisonous
• More acidic than alcohols and water
-
O Na+
OH
+ NaOH
phenol
ROH + NaOH
alcohol
+ H2O
sodium phenoxide
no reaction
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Production of Phenol
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Production of Phenol
• Phenol is obtained from coal tar.
• Several commercial methods are used
to produce phenol synthetically.
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Ethers
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Ethers
Ethers have the general formula
below where both R groups can
be the same or different.
ROR′
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Naming Simple Ethers
Name each alkyl group in alphabetical order followed
by the word ether as shown here.
Use a prefix if both alkyl groups are the same.
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Naming Ethers Using IUPAC Rules
1. Name the longest continuous carbon chain
corresponding to the parent alkane.
2. Change the –yl ending of the other hydrocarbon
group to –oxy to obtain the alkoxy group name.
3. Combine the two names from Steps 1 and 2, giving
the alkoxy name and its position on the longest
carbon chain first, to form the ether name.
For example…
…would be named methoxyethane
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Examples of Naming Alkoxy Groups
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Examples of Naming Ethers
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Structures and Properties
of Ethers
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Properties of Ethers
• Ethers are somewhat more polar than alkanes,
but are much less polar than alcohols.
• Ethers – especially diethyl ether – are
exceptionally good solvents for organic
compounds. H
SO H
3
O
O
H
H
hydrogen
bond
O
H3C
CH2CH3
ether-water
O
H3C
CH2CH3
ether-acid
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Formation of Peroxides from Ethers
• Oxygen of the air slowly reacts with ethers
to form unstable peroxides that are subject
to explosive decomposition.
O
H3CH2C
CH2CH3
+ O2
O
H3CH2C
CHCH3
O-O-H
diethyl ether hydroperoxide
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Preparation of Ethers
84
Preparation of Ethers by Intramolecular Dehydration
Ethers can be prepared by splitting out water from two
molecules of an primary alcohol. This type of reaction is
known as a condensation reaction.
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Thiols
87
Thiols or mercaptans
• contain sulfur
• are similar to alcohols
• contain a thiol (-SH)
group
• often have strong odors
• found in cheese, onions,
garlic, and oysters
• are used to detect gas
leaks
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Thiols
• are named in the
IUPAC system by
adding thiol to the
alkane name of the
longest carbon
chain.
(Methyl Mercaptan)
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Properties of Thiols
1. Foul odors.
2. Oxidation to disulfides:
[O]
2 RSH  R-S-S-R
thiol
disulfide
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• Striped Skunk (Mephitis mephitis) Thiols
H
CH2SH
C
C
CH3
E-2-buten-1-thiol
38-44%
3-methyl-1-butanethiol
18-26%
H
CH3
CH3CHCH2CH2SH
2-quinolinemethanethiol
N
3-12%
CH2SH
92
• For pets that have been sprayed, bathe the
animal in a mixture of 1 quart of 3%
hydrogen peroxide (from drug store), 1/4
cup of baking soda (sodium bicarbonate)
and a teaspoon of liquid detergent. After 5
minutes rinse the animal with water. Repeat
if necessary. The mixture must be used after
mixing and will not work if it is stored for
any length of time. DO NOT STORE IN A
CLOSED CONTAINER - it releases oxygen
gas so it could break the container. This
mixture may bleach the pet's hair.
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• Why tomato juice is believed to eliminate
skunk odor. Bathing an animal in tomato
juice seems to work because at high doses of
skunk spray the human nose quits smelling
the odor (olfactory fatigue). When this
happens, the odor of tomato juice can easily
be detected. A person suffering olfactory
fatigue to skunk spray will swear that the
skunk odor is gone and was neutralized by
the tomato juice. Another person coming on
the scene at this point will readily confirm
that the skunk spray has not been neutralized
by the tomato juice.
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