In concentrated acid, tert-butyl bromide undergoes which mechanism and what is the major product?

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Multiple Choice

In concentrated acid, tert-butyl bromide undergoes which mechanism and what is the major product?

In a strongly acidic, protic medium, a tertiary alkyl bromide ionizes to form a stable tertiary carbocation. SN2 is blocked by the bulky tert-butyl group, so the ionization proceeds rather than direct substitution. Water is scarce in concentrated acid, so capturing the carbocation with water to give tert-butyl alcohol is unlikely; elimination is favored. The tert-butyl carbocation loses a proton from a β-position, forming the alkene. Deprotonation leads to 2-methylpropene (isobutene) as the major product. The carbocation is already tertiary, so there’s no driving rearrangement. Therefore, the mechanism is E1 and the major product is isobutene.

In a strongly acidic, protic medium, a tertiary alkyl bromide ionizes to form a stable tertiary carbocation. SN2 is blocked by the bulky tert-butyl group, so the ionization proceeds rather than direct substitution. Water is scarce in concentrated acid, so capturing the carbocation with water to give tert-butyl alcohol is unlikely; elimination is favored. The tert-butyl carbocation loses a proton from a β-position, forming the alkene. Deprotonation leads to 2-methylpropene (isobutene) as the major product. The carbocation is already tertiary, so there’s no driving rearrangement. Therefore, the mechanism is E1 and the major product is isobutene.

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