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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Isovalent hybridization ： ウィキペディア英語版 Isovalent hybridization In chemistry, isovalent or second order hybridization is an extension of orbital hybridization, the mixing of atomic orbitals into hybrid orbitals which can form chemical bonds, to include fractional numbers of atomic orbitals of each type (s, p, d). It allows for a quantitative depiction of bond formation when the molecular geometry deviates from ideal bond angles. Only bonding with 4 equivalent substituents results in exactly hybridization. For molecules with different substituents, we can use isovalent hybridization to rationalize the differences in bond angles between different atoms. In the molecule methyl fluoride for example, the HCF bond angle (108.73°) is less than the HCH bond angle (110.2°).〔National Institute of Standards and Technology. Listing of Experimental Data for CH3F. ((accessed Feb.19, 2015). ) See table of Internal coordinates.〕 This difference can be attributed to more character in the C−F bonding and more character in the C−H bonding orbitals. The hybridisation of bond orbitals is determined by Bent's rule: "Atomic s character concentrates in orbitals directed toward electropositive substituents". The bond length between similar atoms also shortens with increasing s character. For example, the C−H bond length is 110.2 pm in ethane, 108.5 pm in ethylene and 106.1 pm in acetylene, with carbon hybridizations sp3 (25% s), sp2 (33% s) and sp (50% s) respectively. To determine the degree of hybridization of each bond one can utilize the hybridization parameter (). Utilizing the relationship of the square of the hybridization parameter equals the hybridization index () one can find the degree of hybridization .〔Carroll, F. A. ''Perspectives on Structure and Mechanism in Organic Chemistry'', 2nd ed.; John Wiley & Sons: New Jersey, 2010.〕〔Mislow, K. ''Introduction to Stereochemistry''; W.A. Benjamin Inc: New York. 1965.〕 〔Anslyn, A.V., Dougherty, D.A. ''Modern Physical Organic Chemistry'' 3rd ed; University Science: California. 2006.〕 :$\backslash \; n\; =\; \backslash lambda^2$ The fractional s character can be found using the equation: : $\backslash sum\_\; \backslash frac\; =\; 1$ The fractional character can be found using the equation: :$\backslash sum\_\; \backslash frac\; =\; 1,2\; or\; 3$ These hybridization parameters can then be related to physical properties like bond angles. Using the two bonding atomic orbitals and we are able to find the magnitude of the interorbital angle. The orthogonality condition implies the relation known as Coulson's theorem:〔(Kwan, E.E. Lecture notes Chem 106 (Harvard University) )〕 :$\backslash \; 1\; +\; \backslash lambda\_i\; \backslash lambda\_j\; \backslash cos\; \backslash theta\_i\; =\; 0$ For two identical ligands the following equation can be utilized: :$\backslash \; 1\; +\; \backslash lambda\_i^2\; \backslash cos\; \backslash theta\_\; =\; 0$ The hybridization index cannot be measured directly in any way. However, one can find it indirectly by measuring specific physical properties. NMR coupling constants can be used to provide a measure of bonding density around the nucleus of a bonding carbon atom. This can then be used to find the hybridization because there is character around the nuclei of the bonding electrons. The relationship can be shown with the following equation. :$\backslash \; J\; =\; \backslash frac$ Where is the NMR spin-spin coupling constant of 13C and H. The 13C NMR spectroscopy has been useful in determining quantitative and character in cycloalkanes, showing as you go from cyclopropane to cyclooctane the character increases.〔Carroll, F. A. ''Perspectives on Structure and Mechanism in Organic Chemistry'', 2nd ed.; John Wiley & Sons: New Jersey, 2010.〕〔Anslyn, A.V., Dougherty, D.A. ''Modern Physical Organic Chemistry'' 3rd ed; University Science: California. 2006.〕〔Ferguson, L.N. ''Highlights of Alicyclic Chemistry'', Part 1; Franklin Publishing Company, Inc.: Palisade, NJ, 1973.〕 == References == 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「Isovalent hybridization」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.