Question

How many structural and geometrical isomers are possible for a cyclohexane derivative having the molecular formula, $C_8{H}_{16}$?

Answer 1

Five structural isomers : ethylcyclohexane, $1,1;1,2;1,3-$ and $1,4-$dimethylcyclohexanes.

Six geometrical isomers since each of $1,2;1,3$ and $1,4-$ dimethylcyclohexane has two geomerical (cis and trans) isomers.