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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Interpretation of Anomeric Effect in the N-C-N Unit with the Quantum Theory of Atoms in Molecules
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Interpretation of Anomeric Effect in the N-C-N Unit with the Quantum Theory of Atoms in Molecules

机译：用分子的原子量子理论解释N-C-N单元中的端基效应

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摘要

The conformational preferences of six model compounds for the N-C-N anomeric unit(mefhanediamine,2,2-propanediamine,N,N,N',N'-tetramethyl-methanediairrine,1,3-dizacyclohexane,1,3,5-triazacyclohexane,and 2-aminopiperidine)were analyzed within the framework of the Quantum Theory of Atoms in Molecules.The relative stabilization of the conformers is related to two factors:(i)the reduction of the electron population experienced by the hydrogens of the central methylene when they display more gauche arrangements to lone pairs(lp)and(ii)the reduction of the electron population of aminic hydrogens when the corresponding N-H bond is in a parallel arrangement to the lone pair of another N.The former depletion takes place in lp-N-C-N antiperiplanar dispositions,whereas the latter is shown in lp-N-C-N gauche arrangements.Therefore,we can say that the electron density removed from the central hydrogens is moved to an aminic one on going from an antiperiplanar to a gauche disposition of a lp-N-C-N unit.The relative energies of aminic and central hydrogens in the conformer series is the main factor determining the conformational preference.In contrast to what happens in O-C-O containing compounds(where both N(H)depletions take place in the O-C-O-H gauche dispositions),the stabilization gained by N and C atoms plays a secondary role.This is in line with a general trend exhibited by hydrogens as the most available(less energy cost)atomic basins for receiving or providing electron density along a chemical change.It also explains why the anomeric conformational stabilization due to the N-C-N units is significantly less than that of the O-C-O-units.Moreover,the variations of electron population due to conformational changes are not in keeping with the stereoelectronic model of the anomeric effect,as was previously found for diverse molecules containing the O-C-O anomeric unit.
机译：六种模型化合物对NCN异头单元的构象偏好（甲基苯二胺，2,2-丙二胺，N，N，N'，N'-四甲基-甲二苯胺，1,3-二氮杂环己烷，1,3,5-三氮杂环己烷和（2-氨基哌啶）在分子的原子量子理论框架内进行了分析。构象体的相对稳定与两个因素有关：（i）中心亚甲基的氢在显示时降低了电子数量当相应的NH键与另一个N的孤对平行排列时，更多的gauche排列将对孤对（lp）和（ii）减少氨基氢的电子数量。前一个耗尽发生在lp-NCN的反周平面中因此，可以说从lp-NCN u的反周平面转变为gauche态时，从中心氢中去除的电子密度移动到了一个胺态。构象系列中的胺原子和中心氢的相对能量是决定构象偏好的主要因素。与含OCO的化合物（其中N（H）均发生在OCOH针式化学反应中发生）形成的相反， N和C原子获得的稳定作用起着次要作用，这与氢作为一种最有效的（较少能源成本）原子盆表现出的普遍趋势相一致，该盆用于沿化学变化接收或提供电子密度。由于NCN单元导致的异头构象稳定度明显小于OCO单元包含OCO异头单元。

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