Illustrated Glossary of Organic Chemistry

Steric hindrance: The higher energy price (and slower reaction rate) due to the approach of larger atoms or groups in a chemical reaction, compared to a similar reaction involving smaller atoms or groups. In an SN2 reaction, increasing the number and/or size of alkyl groups on the carbon bearing the leaving group (LG) causes more steric hindrance to backside attack, leading to slower reaction rates:

SN2 reaction rate:




Carbon bonded to leaving group:
Methyl carbon

1o carbon

2o carbon

3o carbon
Steric hindrance to backside attack: Least