Definition of Topicity: A subfield of stereochemistry is a branch of chemistry that is concerned with spatial or three-dimensional orientation of compounds. Within the scope of stereochemistry topicity aims to establish the exact connection between atoms or groups of molecules (substituents) that are attached to the molecule.

Topicity Relationships: The existence of substituents with two or more are classified under four distinct relationships that we’ll look at the next. The four relationships that can be considered are known as homotopic, heterotopic, diastereotopic, enantiotopic and homotopic.

Homotopic Relationships: When two substituents in a compound are similar, they are referred to as homotopic.