Reaction of 3,3-dimethyl-1-butene with hydrogen iodide yields two compounds A and B, each having the molecular formula $\mathrm{C}_{6} \mathrm{H}_{13} \mathrm{I}$, in the ratio $\mathrm{A}: \mathrm{B}=90: 10$. Compound $\mathrm{A}$, on being heated with potassium hydroxide in $n$ -propyl alcohol, gives only 3,3 -dimethyl-1butene. Compound B undergoes elimination under these conditions to give 2,3 -dimethyl2-butene as the major product. Suggest structures for compounds A and B, and write a reasonable mechanism for the formation of each.