Addition reactions are very fast and exothermic. Oxidation of these complexes yields formaldehyde, and reduction yields methane.įree methylene undergoes the typical chemical reactions of a carbene. With strong acids (e.g., fluorosulfuric acid), they can be protonated to give CH Upon treatment with a standard base, complexes with a weak contribution convert to a metal methoxide. A weak contribution, such as in diazomethane, yields mainly substitution reactions, whereas a strong contribution, such as in ethenone, yields mainly addition reactions. Neutral methylene complexes undergo different chemical reactions depending on the pi character of the coordinate bond to the carbon centre. In dilute mixtures with an inert gas, the two states will convert to each other until reaching an equilibrium. The singlet state has a slightly higher energy (by about 9 kcal/mol) than the triplet state, and its H-C-H angle is smaller, about 102°. ) However conversion to a linear configuration requires only 5.5 kcal/ mol. (The correct prediction of this angle was an early success of ab initio quantum chemistry. It has a bent configuration, with H-C-H angle of 133.84 °, and is thus paramagnetic.

The ground state of methylene has an ionisation energy of 10.396 eV. Unsolvated, excited methylene will form stable ground state oligomers. For example, the excited form of ethylene decomposes to acetylene and atomic hydrogen. The excited oligomers, decompose rather than decay to a ground state. Unsolvated methylene will spontaneously autopolymerise to form various excited oligomers, the simplest of which, is the excited form of the alkene ethylene. The singlet state is also more stereospecific than the triplet. For example, reactions of the triplet radical with non-radical species generally involves abstraction, whereas reactions of the singlet non-radical not only involves abstraction, but also insertion or addition. With the singlet non-radical only 38 kJ above the ground state, a sample of methylene exists as a mixture of electronic states even at room temperature, giving rise to complex reactions. The ground state is a triplet radical with two unpaired electrons ( X̃ 3 B 1), and the first excited state is a singlet non-radical ( ã 1 A 1). Many of methylene's electronic states lie relatively close to each other, giving rise to varying degrees of radical chemistry. The methylene molecule (CH 2) was mentioned for the first time by Donald Duck in a comic in 1944. The decomposition can be effected by photolysis, photosensitized reagents (such as benzophenone), or thermal decomposition. Methylene can be prepared, under suitable conditions, by decomposition of compounds with a methylidene or methanediyl group, such as ketene (ethenone) ( CHĢ-I). The reactions of methylene were also studied around 1960, by infrared spectroscopy in frozen gas matrix isolation experiments. TheirĪnalysis of the spectrum lead them to the conclusion that the ground electronic state was anĮlectronic triplet state and that the equilibrium structure was either linear, or else it hadĪ large bond angle of about 140°. The ultraviolet spectrum of gas phase methylene at around 141.5 nm. Produce and spectroscopically characterize the methylene molecule. Using the technique of flash photolysis with the compound diazomethane, Methylene has an electron affinity of 0.65 eV. Methylene is also used as the trivial name for the substituent groups methanediyl ( >CH Although in a context where the radicality is considered, it can also name the non-radical excited state, whereas the radical ground state with two unpaired electrons is named methanediyl. By default, this name pays no regard to the radicality of the methylene. Methylidene is viewed as methane with two hydrogen atoms removed. The systematic names methylidene and dihydridocarbon, valid IUPAC names, are constructed according to the substitutive and additive nomenclatures, respectively. The trivial name carbene is the preferred IUPAC name. : p.7 It is usually detected only at very low temperatures, or as a short-lived intermediate in chemical reactions. It is a colourless gas that fluoresces in the mid-infrared range, and only persists in dilution, or as an adduct. Methylene (IUPAC name: Methylidene, also called carbene or methene) is an organic compound with the chemical formula CHĢ]).

Flip ch2 groups in chemdoodle