Question

What major alkene product is produced by the dehydration of the following alcohols?

a. Cyclohexanol
b. 1-Methylcyclohexanol
c. 2-Methylcyclohexanol
d. 2,2-Dimethylcyclohexanol
e. 1,2-Cyclohexanediol

Answer 1

Here's what I get.

Explanation:

a) Cyclohexanol

Dehydration of an alcohol removes the `"OH"` and the `"H"` on the β-carbon.

b) 1-Methylcyclohexanol

Dehydration of an alcohol gives the more stable alkene (more highly substituted) as the major product.

The major product is 1-methylcyclohexene and methylenecyclohexane is the minor product.

c) 2-Methylcyclohexanol

The more stable (major) alkene product is 1-methylcyclohexene and the minor product is 3-methylcyclohexene.

d) 2,2-Dimethylcyclohexanol

The initially formed 2° carbocation undergoes a methyl shift to form a more stable 3° carbocation, which loses a proton to form 1,2-dimethylcyclohexane as the major product.

The 2° carbocation can rearrange by an alkyl shift to form another 3° cation that loses a proton to form isopropylidenecyclopentane as a minor product.

e) Cyclohexane-1,2-diol

The initial product is an enol, which quickly tautomerizes to the more stable ketone, cyclohexanone.