Transcript Introduction to Organic Chemistry/Practical

Introduction to Organic
Chemistry
Contents
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Nomenclature and Isomerism
Petroleum and Alkanes
Alkenes and Epoxyethane
Haloalkanes
Alcohols
Nomenclature and Isomerism
• The study of the compound of carbon is
called organic chemistry.
• Groups of carbon compounds with the
same functional group are called
homologous series
• Organic compounds are named according
to their longest carbon chain.
Number
of C
atoms
Prefix
1
Meth-
2
3
4
Eth-
Pro-
But-
5
Pent-
6
Hex-
Nomenclature
Homologous Series
General Formula
Name
Functional group
Alkanes
CnH 2n+2
-ane
C –H
Alkenes
CnH2n
-ene
C=C
chloro -, bromo- etc
–Cl or –Br
-ol
–OH
Haloalkanes
Alcohols
CnH2n+1 OH
Aldehyde
-al
O
–C
Ketones
Carboxylic Acids
Esters
-one
CnH 2nCO2H
-oic
H
C=O
O
–C
OH
O
-oate
–C
O–C
Isomerisation
•
Both of the following have four carbon atoms and ten hydrogen atoms they
are called isomers
CH3
CH3 –CH2 –CH2 –CH3
CH3 –CH –CH3
Butane
2-Methyl propane
•The number 2 indicates that the methyl group is attached to the second carbon.
•Carbons are always number so that the lowest numbers appear in the name.
•This type of isomerism is called structural isomerism
•Positional isomers have functional groups at different positions along the chain
•Functional group isomers have different functional groups but have the same
molecular formulae, such as acids and esters
Petroleum and Alkanes
• Petroleum
• Combustion
• Pollution
Petroleum
• Petroleum is another name for crude oil, it is a mixture of
hydrocarbons.
• The hydrocarbons in crude oil all have different boiling
points, this property allows them to be separated by a
process call fractional distillation.
• Fractional distillation produces more long chain
hydrocarbons than the market requires. They are made
into shorter more useful molecules by a process called
cracking.
• Thermal cracking splits the bonds in the hydrocarbon by
a free radical process this uses a lot of energy because
of the high temperatures used.
• Zeolite catalysts can be used to lower the temperature of
the cracking process. It proceeds via ionic intermediates.
Combustion
• In excess oxygen alkanes burn according
to the following equation:
• CnH2n+2 +(1.5n+0.5)O2  nCO2 +(n+1)H2O
• This is called complete combustion,
however if there is in sufficient oxygen
present incomplete combustion can occur.
• CnH2n+2 +(n+0.5)O2  nCO +(n+1)H2O
• With even less oxygen soot is formed.
Pollution
• Many pollutants are formed by the combustion of fossil
fuels. These include soot and carbon monoxide formed
by the incomplete combustion of hydrocarbons.
• Besides making every thing look dirty carbon particulates
in the atmosphere cause breathing problems in those
who are susceptible.
• Carbon monoxide interferes with the blood’s ability to
carry oxygen and in severe case can lead to death.
• Other harmful gases include:
– sulphur dioxide which is formed by the oxidation of impurities in
fossil fuels
– and nitrogen oxides which are formed atmospheric nitrogen is
oxidised during the combustion process.
• Both of these species react with rain water to form acid
rain.
Alkenes and Epoxyethane
• Alkenes are unsaturated. This means that they
do not have the maximum possible number of
hydrogen atoms.
• The double bond in in alkenes is comprised of a
covalent bond and a pi bond. The pi bond has
electron density above and below the covalent
bond and is weaker than a covalent bond.
• Because of the weaker second bond alkenes
are more reactive than alkanes.
• There is no rotation around the double bond, this
causes alkenes to have a planar shape.
Reactions of Alkenes
alkane
+H2 catalyst
Heat & pressure
H H
–C –C –
H
Remember in the
presence of alkenes
bromine water
decolourises
H OH
–C –C –
H n
Catalyst &
heat
+Br2
Br Br
–C –C –
C=C
+steam &
catalyst
+HCl
H Cl
–C –C –
O
Epoxyethane
CH
CH
2
2
• Epoxyethane is produced from ethene
and air or oxygen in the presence of a
silver catalyst.
• The 3-membered ring is strained and
results in high reactivity.
• Epoxyethane is industrially important
because it is hydrolysed to produce
ethane-1,2 diol which is then used in the
production of antifreeze and polyesters.
Haloalkanes
• Haloalkanes contain polar bonds. This is because the
halogen is more electronegative than the carbon.
• This results in the carbon atom being slightly positive and
attractive to electron rich species.
• Reactions resulting from this type of attraction are called
nucleophilic substitution.
C
d+
d-
Br
:CN-
The carbon atom of the CN- ion
donates a pair of electrons to
the haloalkane and the C –Br
breaks with loss of a bromide
ion. A new C –CN bond is
formed.
Elimination
• On heating bromoethane with a strong
base dissolved in ethanol, hydrogen
bromide is eliminated and ethene is
formed:
• CH3CH2Br
CH2=CH2 + HBr
•
KOH/ethanol
Alcohols
H
C
C
H
Primary
H
OH
C
C
C
OH
C
C
C
C
Secondary
Tertiary
OH
Alcohols are classified according to the number of carbon
atoms bonded to the carbon atom adjacent to the OH
group.
Manufacture of Alcohols
• Alcohol for human consumption is
produced by natural fermentation. Yeasts
produce enzymes which catalyse the
reaction called zymases.
• Industrially it cheaper to form ethanol for
solvent by the hydrolysis of ethene.
• It is cheaper to obtain ethanol in this
manner because it is produced in a
continuous process
Reactions of Alcohols
• Oxidation of primary alcohols produces an
aldehyde.
• Aldehydes produce a silver mirror with Tollen’s
reagent
• Secondary and tertiary alcohols produce
ketones upon oxidation these do not give a
silver mirror with ketones.
• Heating alcohols with sulphuric or phosphoric
acid causes them to eliminate water and
produce alkenes
Summary
• Nomenclature and Isomerism
– Naming of organic compounds is systematic it depends on chain length
and functional groups it allows us to identify isomers
• Petroleum and Alkanes
– Most of our hydrocarbon come from crude oil, they are used extensively
for fuel. But this can cause environmental problems
• Alkenes and Epoxyethane
– Alkenes have a double bond which makes them much more reactive.
They are a useful feedstock for the plastics industry
• Haloalkanes
– These molecules have polar bonds which results in them being
susceptible to nucleophilic attack.
• Alcohols
– The reaction of this series of compound depend on whether they are
primary, secondary or tertiary. He primary being much more readily
oxidised than the others.