methinen.
/ˈmɛθʌɪn/, /ˈmiːθʌɪn/, /ˈmɛθiːn/, U.S. /ˈmɛθaɪn/, /ˈmɛθ(ə)n/ Chemistry.
A trivalent group or radical consisting of a carbon and a hydrogen atom, spec. the group =CH—; also called methene or methenyl. Also (esp. in Dye Chemistry): designating a dye, pigment, etc., containing one or more such groups. Frequently attributive.
ΚΠ
1881 H. E. Roscoe & C. Schorlemmer Treat. Chem. III. i. 265 Methine Trisulphonic Acid, CH(SO3H)3, is formed when dry calcium methyl sulphate is heated to 100° with a large excess of fuming sulphuric acid.
1915 P. E. Spielmann tr. V. von Richter Org. Chem. I. 24 By such gradual abstraction of hydrogen, methane yields the following radicals, having different valences:–CH4 Methane, saturated. —CH3 Methyl, univalent radical. =CH2 Methylene, divalent radical. ≡CH Methenyl or Methine, trivalent radical.
1932 Chem. Abstr. 26 730 Exhaustive methylation gave 2 methine bases, one optically active.
1965 J. R. Dyer Applic. Absorption Spectroscopy Org. Compounds iv. 86 Methylene and methine groups attached to carbonyl groups are, as expected, somewhat less shielded.
1966 Nomencl. Org. Chem. (I.U.P.A.C.) (ed. 2) a. 16 (note) The group CH may be referred to as the ‘methine’ group.
1987 A. Nickon & E. F. Silversmith Org. Chem.: Name Game xx. 291 In 1983, Albert Gossauer and Hans Rexhausen..prepared a related 22 π-electron pentacycle with methine bridges between all the pyrrole units, typical of the situation in ordinary porphyrins.
1990 B. Elvers et al. Ullmann's Encycl. Industrial Chem. (ed. 5) A. XVI. 489/2 The first methine dye was discovered in 1856 by G. Williams and was named cyanine.
2000 Jrnl. Agric. & Food Chem. 48 279 Slow protonization of the methine carbon is the primary step in the degradation.
This is a new entry (OED Third Edition, December 2001; most recently modified version published online March 2022).
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