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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Stereoelectronic Effects: The gamma-Gauche Effect in Sulfoxides
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Stereoelectronic Effects: The gamma-Gauche Effect in Sulfoxides

机译：立体电子效应：亚砜中的γ-Gauche作用

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摘要

Reasons for the C-13 NMR gamma-gauche effect in sulfoxides, i.e., the distinct shielding of a carbon beta to a gauche-oriented sulfoxide group were investigated. Several calculated and measured C-13 NMR data of open chain or thiane-derived sulfoxides revealed that an upfield shift is only observed for that gamma-gauche position, in which the respective carbon is anti to the sulfoxide's sulfur lone pair. Carbons in gamma-gauche position, which are synclinal to the lone pair, are not affected. The magnetic anisotropy of the S=O group was examined by generation of iso-chemical-shielding surfaces (ICSSs) and magnetically induced current maps. Stereoelectronic interactions were determined with natural bond orbital (NBO) and natural chemical shielding (NCS) analyses. The gamma-gauche effect is best described by stereoelectronic interactions, especially those of the sulfur's lone pair with antibonding orbitals to a beta-carbon in antiperiplanar orientation. An explanation based on steric interactions, which has frequently been referred to, is not suitable to describe the observed shielding effects. Furthermore, a description of the bonding situation in the S=O group is given. It can be understood as S-O triple bond, where the bond order is significantly reduced by antibonding contributions in some of the occupied molecular orbitals.
机译：研究了C-13NMRγ-Gauche在亚砜中效应的原因，即，碳β对Gauche取向的亚砜基团的不同屏蔽。几个计算和测量的开口链或硫代硫代硫氧化物的C-13 NMR数据显示，仅针对γ-Gauche位置观察到uPField偏移，其中相应的碳是抗亚砜的硫含量对。碳粘土的粘土位置，它们与孤独对同步，不受影响。通过产生ISO化学屏蔽表面（ICSS）和磁感应电流图来检查S = O组的磁各向异性。用天然键（NBO）和天然化学屏蔽（NCS）分析测定立体电子相互作用。 γ-Gauche效应最好通过立体电子相互作用，特别是硫磺酸含量对抗哌甘油取向的β-碳的溶液替氏对β-碳的相互作用描述。基于空间交互的说明，其经常被提及，不适合描述观察到的屏蔽效果。此外，给出了S = O组中的键合情况的描述。它可以理解为S-O三键，其中粘合序列在一些占用的分子轨道中的抗抗渗透贡献显着降低。

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