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Trimethylenemethane (often abbreviated TMM) is a chemical compound with formula . It is a neutral free molecule with two unsatisfied valence bonds, and is therefore a highly reactive free radical. Formally, it can be viewed as an isobutylene molecule with two hydrogen atoms removed from the terminal methyl groups. Trimethylenemethane was first conjectured to be an intermediate in some chemical reactions. It was observed in 1966 by Paul Dowd at very low temperature.〔 Paul Dowd (1972), ''Trimethylenemethane''. Accounts of Chemical Research, volume 5, issue 7, pages 242–248. 〕 == Structure == The unusual electronic structure of Trimethylenemethane was recognized by Moffit and Coulson in 1948.〔〔 C. A. Coulson (1948), Journal de Chimie Physique et de Physico-Chimie Biologique, volume 45, page 243. Cited by Slipchenko and Krylov (2003). 〕 It is a neutral four-carbon molecule containing four pi bonds. When trapped in a solid matrix at about 90 K, the six hydrogen atoms of the molecule are undistinguishable by spectroscopy. Thus, it must be described either as zwitterion, or as the simplest conjugated hydrocarbon that cannot be given a Kekulé structure. It can be described as the superposition of three states: In 1966 Paul Dowd determined with electron spin resonance that this molecule has a triplet ground state ('/), and is therefore a diradical in the stricter sense of the term. Calculations predict that in this state the molecule is planar with three-fold rotational symmetry, with approximate bond lengths 1.40 Å (C–C) and 1.08 Å (C–H). The H–C–H angle in each methylene is about 121 degrees.〔 Lyudmila V. Slipchenko and Anna I. Krylov (2003), ''Electronic structure of the trimethylenemethane diradical in its ground and electronically excited states: Bonding, equilibrium geometries, and vibrational frequencies''. Journal of Chemical Physics volume 118, issue 15, 6874-6883 〕 The molecule also exists as three singlet states with slightly higher energy. According to theoretical calculations, the first one, 1 (1.17 eV above ground), is a closed shell diradical with flat geometry and fully degenerate threefold (D3h) symmetry. The second one, 1 (also at 1.17eV), is an open-shell radical with a D3h-symmetric equilibrium between three equal geometries; each has a longer C–C bond (1.48 Å) and two shorter ones (1.38 Å), and is flat and bilaterally symmetric except that the longer methylene is twisted 79 degrees out of the plane (C2 symmetry). The third singlet state, 2/' (3.88 eV), is also a D3h-symmetric equilibrium of three geometries; each is planar with one shorter C–C bond and two longer ones (C2ν symmetry).〔 The next higher energy states are degenerate triplets, 1 and 2 (4.61 eV), with one excited electron; and a quintet state, (7.17 eV), with the p orbitals occupied by single electrons and D3h symmetry.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「trimethylenemethane」の詳細全文を読む スポンサード リンク
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