Question 1

Why does methyl chloride react faster than tert-butyl chloride in an SN2 reaction?

Accepted Answer

SN2 requires the nucleophile to approach the carbon bearing the leaving group from the backside. tert-Butyl chloride has three methyl groups shielding that approach, whereas methyl chloride leaves the backside path comparatively open, making its SN2 reaction much faster.

Question 2

Why is the SN1 substrate order almost opposite to SN2?

Accepted Answer

The slow step in SN1 is heterolytic cleavage of the carbon-halogen bond to form a carbocation. Tertiary carbocations are more stable because of the +I effect and greater hyperconjugation, so tertiary halides react faster than secondary and primary halides in SN1.

Question 3

What is the difference between the SN1 and SN2 rate laws?

Accepted Answer

SN1 follows rate = k[alkyl halide], because carbocation formation is the rate-determining step and nucleophile is absent from that slow step. SN2 follows rate = k[alkyl halide][nucleophile], because both reactants participate in the concerted transition state.

Question 4

Why is neopentyl chloride very slow in SN2 despite being a primary halide?

Accepted Answer

Its leaving group is attached to a primary carbon, but the adjacent beta-carbon is quaternary and carries three methyl groups. These groups create severe steric hindrance along the backside approach, so neopentyl halides are exceptionally slow in SN2 reactions.

Question 5

Do methyl halides undergo SN1 reactions?

Accepted Answer

No. A methyl carbocation would be extremely unstable because it has no alkyl group available to stabilize the positive charge through the +I effect or hyperconjugation. Therefore, methyl halides do not undergo the usual SN1 pathway.

Steric Block vs Carbocation Stability: Why CH3Cl Beats tert-Butyl Chloride in SN2

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