During dehydration of a tertiary alcohol under concentrated acid, which mechanism is typical and what is the major product type?

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Multiple Choice

During dehydration of a tertiary alcohol under concentrated acid, which mechanism is typical and what is the major product type?

In dehydration of a tertiary alcohol with concentrated acid, the key process is E1: protonation of the OH turns it into a good leaving group, water departs to give a tertiary carbocation, and the rate-determining step is this unimolecular loss of water. From that carbocation, loss of a proton by the conjugate base forms an alkene. Because the reaction proceeds via a carbocation, the double bond tends to form where it is the most substituted, stabilizing the carbocation by hyperconjugation and inductive effects. This is Zaitsev’s rule in action, so the major product is the most substituted alkene. Rearrangements to even more stable carbocations can occur before elimination, often reinforcing formation of the more substituted alkene. E2 isn’t typical here because there isn’t a strong base to pull off a proton in concert with leaving water; SN1 would lead mainly to substitution by the acid rather than elimination; E1cb isn’t applicable under strongly acidic dehydration conditions.

In dehydration of a tertiary alcohol with concentrated acid, the key process is E1: protonation of the OH turns it into a good leaving group, water departs to give a tertiary carbocation, and the rate-determining step is this unimolecular loss of water. From that carbocation, loss of a proton by the conjugate base forms an alkene.

Because the reaction proceeds via a carbocation, the double bond tends to form where it is the most substituted, stabilizing the carbocation by hyperconjugation and inductive effects. This is Zaitsev’s rule in action, so the major product is the most substituted alkene. Rearrangements to even more stable carbocations can occur before elimination, often reinforcing formation of the more substituted alkene.

E2 isn’t typical here because there isn’t a strong base to pull off a proton in concert with leaving water; SN1 would lead mainly to substitution by the acid rather than elimination; E1cb isn’t applicable under strongly acidic dehydration conditions.

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