Answer
a) The structural isomers of $C_{8}H_{18}$ having root name 'hexane' are:
2,3-dimethylhexane; 3,4-dimethylhexane; 2,2-dimethylhexane; 3,3-dimethylhexane; 3-ethylhexane.
b) The structural isomers of $C_{8}H_{18}$ having root name 'pentane' are:
3-ethyl-2-methylpentane; 3-ethyl-3-methylpentane.
All structural formulas are written below:
Work Step by Step
a) Draw 6 C in a straight chain. Then place two methyl groups at C2 and C3 position to get 2,3-dimethylhexane. Again draw 6 C in straight chain and place two methyl groups at C3 and C4 position to get 3,4-dimethylhexane. Now, place two methyl groups at C2 position to get 2,2-dimethylhexane. In the same way, place two methyl groups at C3 position to get 3,3-dimethylhexane.
Now, place an ethyl group at C3 position to get 3-ethylhexane.
b) Draw 5C in straight chain. place one methyl and one ethyl group at C2 and C3 position respectively to get 3-ethyl-2-methylpentane. In the same way, place one methyl and one ethyl group both at C3 position to get 3-ethyl-3-methylpentane.
