In chemistry the descriptor vicinal (from Latin vicinus = neighbor), abbreviated vic, is a descriptor that identifies two functional groups as bonded to two adjacent carbon atoms (i.e., in a 1,2-relationship).
While comparatively less common, the term hominal has been suggested as a descriptor for groups in a 1,3-relationship.
[1] Like other descriptors, such as syn, anti, exo or endo, the description vicinal helps explain how different parts of a molecule are related to each other either structurally or spatially.
The vicinal adjective is sometimes restricted to those molecules with two identical functional groups.
Depending on the other substituents, the vicinal coupling constant is typically a value between 0 and +20 Hz.