ISOMERISM
There are two main types of isomerism
Structural
i.e.
molecular
positional
functional group
Stereoisomerism
i.e.
Geometric and Optical
Molecular
• This is something you are already aware
of from previous work.
• i.e.
•
CH3
• CH3CH2CH2CH3
CH3CHCH3
•
Butane
2-methylpropane
Positional
• You are also aware of most of these from
alcohols and halogenoalkanes
• e.g.
•
Cl
• CH3CH2CH2OH
CH3CHCH3
• Propan-1-ol
2-chloropropane
• However we need to consider aromatics
Positional (aromatics)
•
X
X
•
X
•
•
X
•
• 1,2- (ortho)
1,3- (meta)
X
X
1,4- (para)
Functional group
• There are three main pairs of homologues
involved here, namely:• 1. Alcohols and ethers (alkoxyalkanes)
• 2. Alkanals and alkanones
• 3. Alkanoic acids and esters
Functional group
•
•
•
•
•
•
Alcohols and alkoxyalkanes
e.g.
For the general molecular formula C2H6O
it is possible to have:CH3CH2OH
and
CH3OCH3
Ethanol
Methoxymethane
Problem
• Write out all possible isomers of C4H10O
together with their systematic names.
• CH3CH2CH2CH2OH
• Butan-1-ol
•
CH3
• CH3CHCH2OH
• 2-methylpropan-1-ol
C4H10O
•
•
•
•
•
•
•
CH3CH2CHCH3
OH
Butan-2-ol
CH3
CH3CCH3
OH
2-methylpropan-2-ol
C4H10O (continued)
• CH3CH2OCH2CH3
• Ethoxyethane (diethyl ether)
• CH3OCH2CH2CH3
• Methoxypropane (methyl propyl ether)
Alkanals and alkanones
• For the general molecular formula C3H6O it
is possible to have:• CH3CH2CHO
• Propanal
and
CH3COCH3
Propanone
Problem
• Write out all possible isomers of C4H8O
together with their systematic names
• CH3CH2CH2CHO
CH3CHCHO
•
CH3
• Butanal
2-methylpropanal
•
CH3CH2COCH3
•
Butanone
Alkanoic acids and esters
• For the general molecular formula C2H4O2 it
is possible to have
• CH3COOH
• Ethanoic acid
and
HCOOCH3
Methyl methanoate
Problem
• Write out all possible isomers of C4H8O2
together with their systematic names
• CH3CH2CH2COOH
CH3CHCOOH
•
CH3
• Butanoic acid
2-methylpropanoic acid
•
C4H8O2 (continued)
•
•
•
•
•
•
•
CH3COOCH2CH3
Ethyl ethanaoate
CH3CH2COOCH3
Methyl propanoate
HCOOCH2CH2CH3
Propyl methanoate
There is one other ester which occurs:-
(continued)
•
•
•
•
HCOOCHCH3
CH3
2-methylethyl methanoate