Constitutional (structural) isomers are compounds that have the same molecular formula but a different atom-to-atom bonding sequence. Since constitutional isomers have different physical properties, usually they can be separated easily from each other.
(1)
(2)
(3)
(4)
Constitutional isomers of C5H11N are used below to illustrate different atom-to-atom bonding sequences.
(1)
(2)
(3)
Constitutional (structural) isomers may have the same functional group and the same carbon skeleton (The carbon skeleton shows the arrangement of carbon atoms.), but the functional group is attached to a different carbon atom.
There are only three different constitutional isomers for this carbon skeleton because the two pairs of carbons at either end of the chain are equivalent. The amino group can be on a red carbon or a blue carbon or on a yellow carbon.
Examples of this type are the constitutional isomers (1) and (2).
This type of constitutional isomerism is also known as positional isomerism.
This type of constitutional isomerism is also known as positional isomerism.
There are only three different constitutional isomers for this carbon skeleton because the two pairs of carbons at either end of the chain are equivalent. The amino group can be on a red carbon or a blue carbon or on a yellow carbon.
(4)
Constitutional (structural) isomers may have the same functional group and different carbon skeletons.
Constitutional isomer (4) is a C5H11N isomer with a carbon skeleton different from that of (1), (2) and (3)
Constitutional isomers that have different carbon skeletons are also known as chain isomers.
Constitutional isomers that have different carbon skeletons are also known as chain isomers.
CH3CH2CH2NHCH2CH3
(5)
(5)
Amine constitutional (structural) isomers may have the nitrogen in the middle of the carbon chain.
In this case there are two possible isomers with the N in the middle of the chain because the N can be between the blue and the red carbon OR between the blue and yellow carbons.