The characteristic and important reaction of carboxylic acid derivatives is nucleophillic…

The characteristic and important reaction of carboxylic acid derivatives is nucleophillic acyl substitution which is possible only when the incoming nucleophile (\(\mathrm{Nu}^{\odot}\) or \(\mathrm{HN}_{\mathrm{u}}\)) must not be a much weaker base than the group or substituent attached to the acyl group in the acid derivative. It is a two step process involving nucleophillic attack followed by the loss of the leaving group.
 
Arrange the following in the decreasing order of leaving group ability ?
(I) \(\mathrm{X}^{\ominus}\) (II) \(\stackrel{\ominus}{\mathrm{NH}}_{2}\) (III) \(\stackrel{\ominus}{\mathrm{O}} \mathrm{H}\) (IV) \(\stackrel{\ominus}{\mathrm{OR}}\) 
(V) \(\mathrm{RCOO}^{\ominus}\)