Chapter 20, Problem 20.76P

Treatment of isobutene $\left[{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\text{C}={\text{CH}}_{\text{2}}\right]$ with ${\left({\text{CH}}_{\text{3}}\right)}_{\text{3}}\text{CLi}$ forms a carbanion

that reacts with ${\text{CH}}_{\text{2}}=\text{O}$ to form H after water is added to the reaction mixture. H has a molecular ion in its mass spectrum at $\raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$z$}\right.=86$, and shows fragments at $71$ and $68$. H exhibits absorptions in its IR spectrum at $3600-3200$ and ${\text{1651 cm}}^{-1}$, and has the ${}^1\text{H}$ NMR spectrum given below. What is the structure of H?