What determines the success of substitution reactions? kindly explain.?

Question

What determines the success of substitution reactions? kindly explain.?

Answer 1

If you're talking about nucleophilic substitution reactions (e.g. Sn2 reactions), then you have to consider the strength of the nucleophile and the ability of the leaving group.  If you have a strong nucleophile and a good leaving group, your substitution may be successful.

The transition state of the reaction is also very important.  In Sn1 reactions, a stabilized carbocation increases the likelihood of a successful substitution.

Answer 2

This is a tough one.

It relates to the release of energy being aproximatly equal during the substitution.