vicinalen

Vicinalen is a term used in chemistry to describe substituents, atoms, or functional groups that occupy neighboring positions on adjacent carbon atoms within a molecule. The term derives from the Latin vicinus, meaning neighbor or nearby. In practice, vicinal relationships are central to describing structure, reactivity, and stereochemistry in organic compounds.

In common usage, vicinal motifs include vicinal dihalides, vicinal diols, and vicinal trihalides, where substituents sit on two consecutive carbon atoms. In nuclear magnetic resonance (NMR) spectroscopy, protons on adjacent carbons exhibit vicinal coupling, producing characteristic J-couplings typically denoted as 3J values. These couplings provide information about the relative arrangement of neighboring atoms. Vicinal relationships also influence reaction pathways, such as neighboring group effects (anchimeric assistance), where a nearby atom or group participates in the mechanism via a vicinal intermediate and can accelerate or direct a transformation.

Stereochemical considerations are prominent with vicinal relationships. In cyclic systems, substituents on adjacent carbons can be oriented on the same side (syn) or opposite sides (anti), affecting ring geometry and reactivity. In acyclic compounds, vicinal two-carbon relationships determine relative configurations between neighboring stereocenters.

In synthesis, vicinal functionalization enables the stepwise introduction or modification of groups on adjacent carbons, facilitating complex molecule construction. While “vicinalen” appears in some languages as a form referring to vicinal concepts, the core idea remains the adjacency of functional groups on neighboring carbon atoms, with broad implications for structure, spectroscopy, and chemical reactivity.