Question

poor leaving group in nucleophilic substitutions reaction

Answer 1

Answer:

A leaving group is a nucleophile acting in reverse; it accepts a lone pair as the bond between it and its neighbor (usually carbon for our purposes) is broken.

So what makes a good leaving group?

The “happier” and more stable that lone pair is, the better a leaving group it will be. The most predictive rule for leaving group ability is….

Good leaving groups are weak bases.

Why?

Think about the dissociation of an acid H–A to give H+ and A– . The species A– is the conjugate base of HA. It accepts a pair of electrons from the H-A bond. It’s a base acting in reverse.

The more stable A- is, the greater the equilibrium constant will be that favors dissociation to give A- .