What are leaving groups in nucleophilic substitution reactions?

1 Answer
Jan 7, 2015

The leaving group is the part of the substrate that is missing at the end of the reaction.

The equation for a typical nucleophilic substitution reaction is

Nu⁻ + R-L → Nu-R + L⁻

Nu⁻ is the nucleophile, and R-L is the substrate.

The L group is missing from the substrate, so L is the leaving group.

Suppose the reaction had been

N≡C⁻ + CH₃CH₃CH₂-Br → CH₃CH₂CH₂-C≡N + Br⁻

The product no longer has the Br atom that was in the CH₃CH₃CH₂-Br.

The leaving group was the Br atom.

Here's a video on leaving groups.