Question

Which of the following statements about an SN2 reaction is not correct?

a) Primary alkyl halides are more reactive than tertiary alkyl halides.
b) It has a one-step mechanism.
c) It has a unimolecular rate-determining transition state.
d) All of the above.

Answer 1

The incorrect statement about an SN2 reaction is c) It has a unimolecular rate-determining transition state, as SN2 reactions have a bimolecular rate-determining step.

Step-by-step explanation:

The statement about an SN2 reaction that is not correct is option c) It has a unimolecular rate-determining transition state. SN2 reactions feature a bimolecular rate-determining step which involves the simultaneous attack of the nucleophile and the departure of the leaving group in one concerted step.

In contrast, SN1 reactions have a unimolecular rate-determining step, involving the formation of a stable carbocation intermediate before the nucleophile attacks.

For an SN2 reaction, primary alkyl halides are indeed more reactive than tertiary alkyl halides due to steric hindrance in the latter, which prevents the nucleophile from effectively approaching the substrate.

This explains why statement a) is correct. Additionally, the SN2 mechanism indeed has a one-step mechanism which is typically associated with inversion of stereochemistry at the reaction site, confirming that statement b) is also correct.