Question

How many cycloalkene isomers exist of $C_5{H}_8$ which contain at least one methyl locant directly present on the ring?

• A. 7
• B. 4
• C. 5
• D. 6

Answer 1

The correct option is C 5

For a compound with molecular formula $C_c{H}_h{X}_x{N}_n{O}_o$
$\text{Degree of unsaturation}=(c+1)-\frac{h}{2}-\frac{x}{2}+\frac{n}{2}$
Where, X = Halogen
c=number of carbon atom
h=number of hydrogen atom
n=number of nitrogen atom
o=number of oxygen atom
In $C_5{H}_{8}O$
$\text{Degree of unsaturation}=(5+1)-\frac{8}{2}=2$
Compound has one degree of unsaturation, it can have one ring and one double bond.
Atleast one methyl is also there on ring thus all five possible isomers are