vicinal

1. Of, belonging to, or restricted to a limited area or neighborhood; local.
2. Relating to or being a local road.
3. Mineralogy. Approximating, resembling, or taking the place of a fundamental crystalline form or face.
4. Chemistry. Of or relating to the consecutive positions of substituted elements or radicals on a benzene ring.

[Latin vīcīnālis, from vīcīnus, neighboring. See vicinity.]

Designating a molecule in which two atoms or groups are linked to adjacent atoms. For example, 1,2-dichloroethane (CH₂ClCH₂Cl) is a vicinal (or vic) dihalide and can be named vic-dichloroethane.

The adjective has one meaning:

Meaning #1: belonging to or limited to a vicinity
  Pertains to noun: vicinity (meaning #1)

2,3-dibromobutane (at left) and 1,3-dibromobutane (at right). Carbons containing vicinal functional groups are marked in red.

In chemistry vicinal (from Latin vicinus = neighbour) stands for any two functional groups bonded to two adjacent carbon atoms. For example the molecule 2,3-dibromobutane carries two vicinal bromine atoms and 1,3-dibromobutane does not.

Likewise in a gem-dibromide the prefix gem, an abbreviation of geminal, signals that both bromine atoms are bonded to the same atom. For example, 1,1-dibromobutane is geminal.

Like other such concepts 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. The term can also be extended to substituents on aromatic rings.

See also

• Geminal

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