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Silene, or silalkenes,〔Philip P. Power "pi-Bonding and the Lone Pair Effect in Multiple Bonds between Heavier Main Group Elements" Chemical Reviews, 1999, 99, 3462. 〕 are unsaturated hydrosilicons, which means that they consist only of hydrogen and silicon atoms and all bond, with the exception of one double bond, are either single or double bonds. By definition cycles are excluded, so that the silenes comprise homologous series of inorganic compounds with the general formula , ''k'' > 0, where ''k'' is defined as the number of double bonds. There are no commercial sources. Each silicon atom has three or four bonds (either Si-H, Si-Si, or Si=Si), and each hydrogen atom is joined to a silicon atom (H-Si bonds). A series of linked silicon atoms is known as the silicon skeleton or silicon backbone. The number of silicon atoms is used to define the size of the silene (e.g. Si2-silene). A ''silenyl'' group, is a functional group or side-chain with the general formula , ''k'' > 0, where ''k'' is defined as the number of double bonds, for example an disilenyl or trisil-1-en-1-yl group. The simplest silene is (the parent molecule) is disilene, . There is no limit to the number of silicon atoms that can be linked together, the only limitation being that the molecule is acyclic, is, unsaturated, and is a hydrosilicon. For bridged silenes, the Bredt's rule states that a double bond cannot be placed at the bridgehead of a bridged ring system, unless the rings are large enough (8 or more atoms). Aromatic compounds are often drawn as cyclic silenes, but their structure and properties are different and they are not considered to be silenes. Although silenes is mainly of theoretical interest, substituted silenes are well known class of organosilicon compounds. == Structure == Like single covalent bonds, double bonds can be described in terms of overlapping atomic orbitals, except that, unlike a single bond (which consists of a single sigma bond), a silicon-silicon double bond consists of one sigma bond and one pi bond. This double bond is stronger than a single covalent bond and also shorter. Each silicon of the double bond uses its three ''sp2'' hybrid orbitals to form sigma bonds to three atoms. The unhybridized 3''p'' atomic orbitals, which lie perpendicular to the plane created by the axes of the three sp² hybrid orbitals, combine to form the pi bond. This bond lies outside the main Si—Si axis, with half of the bond on one side and half on the other. Rotation about the silicon-silicon double bond is not restricted because it involves breaking the pi bond, which requires a small amount of energy. As a consequence, substituted alkenes may not exist as one of two isomers. It is certainly possible to twist a double bond. 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「Silenes」の詳細全文を読む スポンサード リンク
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