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Bent's rule describes and explains the relationship between the isovalent hybridization of central atoms in molecules and the electronegativities of substituents. The rule was stated by Henry Bent as follows: "Atomic s character concentrates in orbitals directed toward electropositive substituents".〔 The chemical structure of a molecule is intimately related to its properties and reactivity. Valence bond theory proposes that molecular structures are due to covalent bonds between the atoms and that each bond consists of two overlapping and typically hybridised atomic orbitals. Traditionally, p-block elements in molecules are assumed to hybridise strictly as sp''n'', where ''n'' is either 1, 2, or 3. In addition, the hybrid orbitals are all assumed to be equivalent (i.e. the sp''n'' orbitals have the same p character). Results from this approach are usually good, but they can be improved upon by allowing hybridised orbitals with noninteger and unequal p character. Bent's rule provides a qualitative estimate as to how these hybridised orbitals should be constructed. Bent's rule is that in a molecule, a central atom bonded to multiple groups will hybridise so that orbitals with more s character are directed towards electropositive groups, while orbitals with more p character will be directed towards groups that are more electronegative. By removing the assumption that all hybrid orbitals are equivalent sp''n'' orbitals, better predictions and explanations of properties such as molecular geometry and bond strength can be obtained. Bent's rule can be generalized to d-block elements as well. The hybridisation of a metal center is arranged so that orbitals with more s character are directed towards ligands that form bonds with more covalent character. Equivalently, orbitals with more d character are directed towards groups that form bonds of greater ionic character.〔 == History == In the early 1930s, shortly after much of the initial development of quantum mechanics, those theories began to be applied towards molecular structure by Pauling,〔 〕 Slater,〔 〕 Coulson,〔 〕 and others. In particular, Pauling introduced the concept of hybridisation, where atomic s and p orbitals are combined to give hybrid sp, sp2, and sp3 orbitals. Hybrid orbitals proved powerful in explaining the molecular geometries of simple molecules like methane (tetrahedral with an sp3 carbon). However, slight deviations from these ideal geometries became apparent in the 1940s. A particularly well known example is water, where the angle between hydrogens is 104.5°, far less than the expected 109.5°. To explain such discrepancies, it was proposed that hybridisation can result in orbitals with unequal s and p character. A. D. Walsh described in 1947〔 a relationship between the electronegativity of groups bonded to carbon and the hybridisation of said carbon. Finally, in 1961, Henry A. Bent published a major review of the literature that related molecular structure, central atom hybridisation, and substituent electronegativities 〔 and it is for this work that Bent's rule takes its name. 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「Bent's rule」の詳細全文を読む スポンサード リンク
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