A student was studying terpene synthesis, and she wanted to make the compound shown here. First she converted 3-bromo-6-methylcyclohexene to alcohol A. She heated alcohol A with sulfuric acid and purified one of the components (compound B) from the resulting mixture. Compound B has the correct molecular formula for the desired product.
(a) Suggest how 3-bromo-6-methylcyclohexene might be converted to alcohol A.
(b) The UV spectrum of compound B shows at 269 nm. Is compound B the correct product? If not, suggest a structure for compound B consistent with these UV data.
(c) Propose a mechanism for the dehydration of alcohol A to compound B.
(a) The 3-bromo-6-methylcyclohexene reacts with Mg metal to form an organometallic compound.
The organometallic compound reacts with acetone followed by hydrolysis to form an alcohol.
(b) Given the UV spectral data, the required compound (B) is given below. Its value is 271 nm because this value is approximately identical to given value (269 nm).
(c) The alcohol reacts with sulfuric acid followed by the hydride shift to form a tertiary carbocation.
The nucleophile abstracts a proton from the carbon adjacent to the carbocation to form compound B.