Regiochemistry Definition:

A term describing a consideration that must be taken into account for a reaction in which two or more constitutional isomers can be formed.

Regiochemistry Explained:

Regioselectivity is the preference for one orientation over another in the arrangement of a reaction product. In alkene addition reactions as an example refers to which part the reagent adds to which part of the double bond. This is also called the “orientation of addition.”