Compared to a ketone adding a leaving group on a carboxylic acid derivative increases the number of resonance structures and  decreases the overall partial positive at the carbonyl carbon.  This is because the leaving group acts as an electron donor by resonance. If the leaving group  is O or N resonance is efficient due to good orbital overlap, and the leaving group ability is [ Select ] good bad cannot say due to pKa. This [ Select ] speeds up slows down does not affect. nucleophilic acyl substitution.