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Geminal
In chemistry, the descriptor geminal refers to the relationship between two atoms or functional groups that are attached to the same atom. The word comes from Latin gemini meaning “twins”. A geminal diol, for example, is a diol (a molecule that has two alcohol functional groups) attached to the same carbon atom, as in methanediol. Also the shortened prefix gem may be applied to a chemical name to denote this relationship, as in a gem-dibromide for “geminal dibromide”.
The concept is important in many branches of chemistry, including synthesis and spectroscopy, because functional groups attached to the same atom often behave differently from when they are separated. Geminal diols, for example, are easily converted to ketones or aldehydes with loss of water.
The related term vicinal refers to the relationship between two functional groups that are attached to adjacent atoms. The relative arrangement of two functional groups can also be described by the descriptors α and β.
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Geminal (adjective)
Describing identical atoms or groups attached to the same atom in a molecule
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Vicinal (adjective)
Of or pertaining to a neighborhood; neighboring.
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Vicinal (adjective)
Describing identical atoms or groups attached to nearby (especially adjacent) atoms in a molecule.
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Vicinal (adjective)
Describing subordinate planes on a crystal, which are very near to the fundamental planes in angles, and sometimes take their place.
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Geminal (adjective)
denoting substituent atoms or groups, especially protons, attached to the same atom in a molecule.
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Vicinal (adjective)
neighbouring; adjacent.
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Vicinal (adjective)
relating to or denoting substituents attached to adjacent atoms in a ring or chain.
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Vicinal (adjective)
(of a railway or road) serving a neighbourhood; local.