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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >G2 Molecular Orbital Investigation of Torsional Barriers in H_2Al = XHCH_3 and H_2Al = YCH_3 (X = N,P, and As; Y = O,S, and Se) Systems
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G2 Molecular Orbital Investigation of Torsional Barriers in H_2Al = XHCH_3 and H_2Al = YCH_3 (X = N,P, and As; Y = O,S, and Se) Systems

机译：H_2Al = XHCH_3和H_2Al = YCH_3（X = N，P和As; Y = O，S和Se）系统中扭转势垒的G2分子轨道研究

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摘要

Structures of H_2Al = XHCH_3 and H_2Al = YCH_3 (X = N,P, and As; Y = O, S, and Se) systems wee investigated using ab initio method at the G2 level to study the conformational preferences of the methyl group. In all of the molecules, the eclipsed C_s symmetry arrangement (one of the C-H bonds of the methyl group eclipses Al = X(Y)) conformer is found to be more stable than the staggered C_s symmetry arrangement (the C-H bond is trans to Al = X(Y)) conformer. The G2 energetic results show that the 3-fold methyl rotational barrier is found to decrease as the electronegativity of X(Y) increases. They also show that this 3-fold methyl rotational barrier decreases when descending in the corresponding periodic table column, from nitrogen (or oxygen) to arsenic (or selenium) atoms. A qualitative argument based on the interaction of the fragment orbitals is used to rationalize the observed trends. The thermodynamic values of the methyl transfer reactions are examined. The possible dissociation processes of H_2Al = XH(Y)CH_3 systems into HAlXH(Y) and CH_4 or into HAlXCH_3 and molecular H_2 are also examined and reported.
机译：我们使用从头算方法在G2层次上研究了H_2Al = XHCH_3和H_2Al = YCH_3（X = N，P和As; Y = O，S和Se）系统的结构，以研究甲基的构象偏好。在所有分子中，发现错配的C_s对称排列（甲基食盐的CH键之一Al = X（Y））构型比交错的C_s对称排列更稳定（CH键反成了Al = X（Y））构象异构体。 G2的能量结果表明，随着X（Y）电负性的增加，3倍的甲基旋转势垒会降低。他们还表明，当在相应的周期表列中从氮（或氧）到砷（或硒）原子下降时，这种3倍的甲基旋转势垒会降低。基于碎片轨道相互作用的定性论证被用于合理化观察到的趋势。检查了甲基转移反应的热力学值。还检查并报告了H_2Al = XH（Y）CH_3系统可能分解为HAlXH（Y）和CH_4或分解为HAlXCH_3和分子H_2的过程。

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