In a nucleophilic substitution reaction, complete inversion of configuration at the reactive carbon atom is observed. Would the mechanism most likely be SN1 or SN2? Briefly explain your answer.

The mechanism is most likely to be SN2.

Explanation:

SN1 reaction is a two step reaction in which the first step is carbocation formation which is planar. The nucleophile can attack from either sides of it resulting in recemic mixture (both retention and inversion product is formed).

But SN2 reaction is a single-step process that is the leaving group leaves and the nucleophile attacks at the same instant. Hence the nucleophile attacks from the opposite side of the leaving group resulting in inversion product.

Hence mechanism is SN2.

SN2 mechanism

Explanation:

This is a situation were substitution occurs with inversion of configuration at the chiral centers which proceed through concerted backside attack where nucleophile approaches the alkyl halides 180° from c-br bond, as c - (nucleophile) bond forms, the c - (leaving group) bond breaks.