Chapter 13, Problem 13.55P

Reaction of pentanoyl chloride $\left({\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{COCl}\right)$ with lithium dimethyl cuprate $\left[\text{LiCu}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\right]$ forms a compound J that has a molecular ion in its mass spectrum at $100$, as well as fragments at $m\text{/}z=\text{85, 57}$ and $43$ (base). The IR spectrum of $J$ has strong peaks at. Propose a structure for $J$