Question

The reaction of 2,2-dimethyl-1-piopanol with HBr is very slow and gives 2-bromo- 2-methyIbutane as the major product. Give a mechanistic explanation for these observations. Select all that apply. Stereoelectronic effects result in an antic op lanar rearrangement of the carbon skeleton. Steric hindrance prevents nucleophilic attack. The mechanism requites the development of an unstable positively charged species in the transition state. The mechanism results in a carbocation rearrangement in which a methyl shift occurs. The mechanism requires dissociation of a poor leaving group.

Answer 1

The reaction of 2,2-dimethyl-1-propanol with HBr is slow due to steric hindrance and involves the formation of a more stable tertiary carbocation followed by a methyl shift, resulting in 2-bromo-2-methylbutane.

Step-by-step explanation:

The reaction of 2,2-dimethyl-1-propanol with HBr to yield 2-bromo-2-methylbutane involves several considerations:

Steric hindrance prevents nucleophilic attack at the more substituted carbon due to the bulky methyl groups present.

The formation of a carbocation is necessary, which is an unstable positively charged species. 2,2-dimethyl-1-propanol forms a tertiary carbocation during the reaction, which is more stable than a primary or secondary carbocation and can therefore form despite the energy barrier.

A carbocation rearrangement occurs with a methyl shift, which explains the formation of 2-bromo-2-methylbutane as the major product. This rearrangement follows an SN1 mechanism, as opposed to an SN2 mechanism, which is not sterically favored in this case.

Answer 2

Correct option : "The mechanism results in a carbocation rearrangement in which a methyl shift occurs"

Step-by-step explanation:

In the first step, 2,2-dimethyl-1-propanol gets protonated.

In the second step, a carbocationic intermediate is produced from removal of
`H_(2)O`.

In the third step, shifting of methyl group occurs to produce more stable carbocationic intermediate.

In the fourth step,
`Br^(-)` attacks the stable carbocation to produce 2-bromo-2-methylbutane.

So, correct option : "The mechanism results in a carbocation rearrangement in which a methyl shift occurs"

Full reaction mechanism has been shown below.