Methine group

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Methine or methylylidene (IUPAC)

In chemistry, a methine group or methine bridge is a trivalent functional group =CH−, derived formally from methane. It consists of a carbon atom bound by two single bonds and one double bond, where one of the single bonds is to a hydrogen. The group is also called methyne or methene; its IUPAC systematic name is methylylidene or methanylylidene[1]

This group is sometimes called "methylidyne", however that name belongs properly to either the methylidyne group ≡CH (connected to the rest of the molecule by a triple bond) or to the methylidyne radical CH (the two atoms as a free molecule with dangling bonds).

The name "methine" is also widely used in non-systematic nomenclature for the methanetriyl group (IUPAC): a carbon with four single bonds, where one bond is to a hydrogen (>CH−).[2]

Overlapping methines[edit]

Two or more methine bridges can overlap, forming a chain or ring of carbon atoms connected by alternating single and double bonds, as in piperylene H
2
C=CH–CH=CH–CH
3
, or the compound

Methine chain.svg

Every carbon in this molecule is a methine carbon, except for three; two that are attached to the two nitrogens and not to any hydrogens, and the one attached to the nitrogen, which is attached to two hydrogens (far right). There is a five carbon poly-methine chain in the center of this molecule.

Chains of alternating single and double bonds often form conjugated systems. When closed, as in benzene (=CH–CH=)
3
, they often give aromatic character to the compound.

See also[edit]

References[edit]

  1. ^ (2007) Methanylylidene group in the Chemical Entities of Biological Interest (ChEBI) database. Accessed on 2015-03-05.
  2. ^ (2007) Methanetriyl group in the Chemical Entities of Biological Interest (ChEBI) database. Accessed on 2015-03-05.