Question

Find all the structural isomer of C₄H₆. 

Answer 1

Total unsaturation of C₄H₆ = 2 

Possibility = one triple bond, or 2 double bond or (one ring + one double bond) 

Possibility for triple bond

Possibility for two double bonds

Possible cyclic structures: 

Total structural isomers = 4(acyclic) + 5(cyclic) = 9