In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
, a methine group or methine bridge is a trivalent
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...
, derived formally from
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
. It consists of a
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
atom bound by two single
bond
Bond or bonds may refer to:
Common meanings
* Bond (finance), a type of debt security
* Bail bond, a commercial third-party guarantor of surety bonds in the United States
* Chemical bond, the attraction of atoms, ions or molecules to form chemica ...
s and one
double bond
In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...
, where one of the single bonds is to a
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
. The group is also called methyne or methene; its
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
systematic name is methylylidene or methanylylidene
[
(2007]
''Methanylylidene group''
in the Chemical Entities of Biological Interest (ChEBI) database. Accessed on 2015-03-05.
This group is sometimes called "methylidyne", however that name belongs properly to either the
methylidyne group (connected to the rest of the molecule by a triple bond) or to the
methylidyne radical
Methylidyne, or (unsubstituted) carbyne, is an organic compound whose molecule consists of a single hydrogen atom bonded to a carbon atom. It is the parent compound of the carbynes, which can be seen as obtained from it by substitution of other ...
(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 atom with four single bonds, where one bond is to a hydrogen ().
[
(2007]
''Methanetriyl group''
in the Chemical Entities of Biological Interest (ChEBI) database. Accessed on 2015-03-05.
Overlapping methines
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
Piperylene or 1,3-pentadiene is an organic compound with the formula . It is a volatile, flammable hydrocarbon. It is one of the five positional isomers of pentadiene.
Reactions and occurrence
Piperylene is a typical diene. It forms a sulfo ...
, or the compound
Every carbon atom in this molecule is a methine carbon atom, except for three; two that are attached to the two
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
atoms and not to any hydrogen atoms, and the carbon attached to the nitrogen atom, which is attached to two hydrogen atoms (far right). There is a five-carbon-atom 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
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
, they often give
aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
character to the compound.
See also
*
Methyl group
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...
−
*
Methylene group
In organic chemistry, a methylene group is any part of a molecule that consists of two hydrogen atoms bound to a carbon atom, which is connected to the remainder of the molecule by two single bonds. The group may be represented as , where the '< ...
or methylidene =
*
Methylene bridge
In organic chemistry, a methylene bridge, methylene spacer, or methanediyl group is any part of a molecule with formula ; namely, a carbon atom bound to two hydrogen atoms and connected by single bonds to two other distinct atoms in the rest of t ...
or methanediyl −−
*
Methanetriyl group
In organic chemistry, a methine group or methine bridge is a trivalent functional group , 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. T ...
>CH−
*
Methylylidyne group ≡C−
References
Functional groups
Substituents
{{Functional Groups