Q 11-11-41 E-b - Organic Chemistry (Mcmurry)

Question

Which compound in each of the following pairs will react faster in an S_N2 reaction with OH^- ?

(b) CH₃CH₂I in ethanol or dimethyl sulfoxide 

Step-by-Step Solution

Answer

CH₃CH₂I

S N 2 reaction

An old bond is broken and a new bond is formed in this nucleophilic substitution reaction. This occurs simultaneously. The reaction is therefore single-step.

The two reacting species are involved in the rate determining steps.

Nucleophile

Nucleophiles are the negatively charged ions or the neutral species having the lone pair of electrons ready for bonding.

Species react faster with OH -

If the species is a better leaving group, it reacts faster with the nucleophile. 

I am a better leaving group than dimethyl sulfoxide (DMSO) in ethanol, aprotic solvent, and form hydrogen bonds with hydroxide. It decreases the reactivity of the reaction.

CH₃CH₂I shows fast reaction than DMSO