Question

Number substituted cycloalkenes in the way that gives the carbon atoms of the double bond the $1$ and $2$ positions and that also gives the substituent groups the lower numbers at the first point of difference. With substituted cycloalkenes it is not necessary to specify the position of the double bond since it will always being with $C1$ and $C2$. The examples shown here illustrate the application of these rules:

Answer 1

The IUPAC Name of 1st structure is 1-methylcyclopentene because the compound is cyclic in nature and contains 5 carbons and double bond at 1 and 2 and a methyl group is attached to 1 position. The numbering of substituents should be such that it gets lowest position.

The IUPAC Name of 2nd structure is 3,5 dimethylcyclohexene because the compound is cyclic compound and contain 6 carbon and one double bond.And the two methyl substituents are numbered in such a way that they get the lowest position having double bond at 1 and 2 position.