MCAT Organic Chemistry Question — Alcohol Reactions

Considering all “-R” groups to be alkyl groups, which alcohol is most reactive in an S_N1 reaction with HCl?

a) primary alcohol

b) secondary alcohol

c) tertiary alcohol

d) number of substituent groups does not affect alcohol reactivity

Explanation

Only tertiary alcohols form a carbocation stable enough for an S_N1 mechanism. Primary and secondary alcohols react too slowly by S_N1 mechanisms to for significant amounts of product in comparison with tertiary alcohols.

a) primary alcohol, incorrect, Primary alcohols do not form stable carbocations necessary for the S_N1 mechanism with HCl.

b) secondary alcohol, incorrect, Same reason as choice a).

c) tertiary alcohol, correct.

d) number of substituent groups does not affect alcohol reactivity, incorrect, Substituent groups strongly affect alcohol reactivity, and primary and secondary alcohols do not react significantly with HCl by an S_N1 mechanism.

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