Question

multiple answer 1 point
which of the following would increase the likelihood of an s_n1 reaction over an s_n2 reaction? (select all that apply)
a polar aprotic solvent
a tertiary carbon center
a bulky alkyl group on the substrate
a weak nucleophile

Explanation:

Step1: Solvent effect

$\ce{S_N1}$ reactions prefer polar protic solvents (stabilize carbocation), while polar aprotic solvents favor $\ce{S_N2}$. So A is wrong.

Step2: Carbon center structure

Tertiary carbon centers form more stable carbocations (key in $\ce{S_N1}$), promoting $\ce{S_N1}$ over $\ce{S_N2}$. So B is correct.

Step3: Steric hindrance

Bulky alkyl groups on substrate hinder back - side attack (characteristic of $\ce{S_N2}$), making $\ce{S_N1}$ more likely. So C is correct.

Step4: Nucleophile strength

Weak nucleophiles are less likely to participate in the one - step $\ce{S_N2}$ (which needs a strong nucleophile for back - side attack). $\ce{S_N1}$ is a two - step process (formation of carbocation first, then nucleophile attack), so weak nucleophile favors $\ce{S_N1}$. So D is correct.

Answer:

B. A tertiary carbon center, C. A bulky alkyl group on the substrate, D. A weak nucleophile