Chapter 14, Problem 14.70P

Treatment of $\text{butan}-2-\text{one}$ $\left({\text{CH}}_{\text{3}}{\text{COCH}}_{\text{2}}{\text{CH}}_{\text{3}}\right)$ with strong base followed by ${\text{CH}}_{\text{3}}\text{I}$ forms a compound Q, which gives a molecularion in its mass spectrum at $86$. The IR ( $>1500{\text{cm}}^{-1}$ only ) and ${}^1\text{H}\text{NMR}$ spectrum of Q are given below. What is the structure of Q?