In this type of substitution reaction, one group of the substrate participates initially in the reaction and thereby affects the reaction. Due to NGP, the reaction rate gets increased by many folds. 
A classic example of NGP is the reaction of a sulfur or nitrogen mustard with a nucleophile, the rate of reaction is much higher for the sulfur mustard and a nucleophile than it would be for a primary or secondary alkyl chloride without a heteroatom.
 reacts with water 650 times faster than .