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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Conformational Transformations in Aromatic Nitroso Oxides
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Conformational Transformations in Aromatic Nitroso Oxides

机译：一氧化二氮的构象转化

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摘要

A systematic theoretical study on conformational transformations of monosubstituted (ortho- and para-) aromatic nitroso oxides R-C6H4NOO was performed. The existence of two rotation axes enables two types of conformational transitions in substituted arylnitroso oxides: trans/cis (rotation around the N-O bond) and syn/anti (rotation around the C-N bond, which is important in ortho isomers). The complete set of conformers was localized for R-C6H4NOO using four selected density functional (M06-L, mPWPW91, OLYP, and HCTH) and augmented polarization basis set of triple splitting. It was found that the activation enthalpy of the trans-cis conformational transition is nearly insensitive to the nature of R and ranges within 58-60 kJ/mol for para isomers. The ortho substituent has an insignificant effect on Delta H-trans -> cis(not equal): it increases this value by similar to 5 kJ/mol in syn isomers and decreases it by similar to 3 kJ/mol in anti isomers. On the contrary, the syn-anti conformational barrier is considerably affected by the substituent R; an increase in the electron-withdrawing properties of R decreases Delta H-syn -> anti(not equal). The activation enthalpies grow with increasing polarity of the solvent, as it was found using IEFPCM calculation. The values of relaxation time for all conformational equilibria were calculated and compared with known lifetimes of aromatic nitroso oxides. Our results suggest that syn/anti transitions occur fast enough in the scale of the experimental lifetime. However, trans/cis transformations proceed more slowly. And under certain conditions discussed in the paper, the rate of this conformational transition limits that of irreversible decay of nitroso oxide.
机译：对单取代的（邻和对）芳族亚硝基氧化物R-C6H4NOO的构象转化进行了系统的理论研究。两个旋转轴的存在可实现取代的芳基亚硝基氧化物中的两种构象转变：反式/顺式（围绕N-O键旋转）和顺式/反式（围绕C-N键旋转，这在邻位异构体中很重要）。使用四个选定的密度函数（M06-L，mPWPW91，OLYP和HCTH）和增强的三重分裂极化基础集，对R-C6H4NOO定位完整的构象体集。发现反式顺式构象转变的活化焓对R的性质几乎不敏感，并且对位异构体的活化焓在58-60kJ / mol的范围内。邻位取代基对Delta H-反式->顺式（不相等）的影响不显着：在顺式异构体中，该值增加约5 kJ / mol，在反式异构体中，降低约3 kJ / mol。相反，顺-反构象势垒受到取代基R的很大影响。 R的吸电子性质的增加降低了ΔH-syn→反（不相等）。使用IEFPCM计算发现，活化焓随溶剂极性的增加而增长。计算所有构象平衡的弛豫时间值，并将其与芳香族亚硝基氧化物的已知寿命进行比较。我们的结果表明，顺/反过渡在实验寿命的范围内发生得足够快。但是，反式/顺式转换的进行速度较慢。在本文讨论的某些条件下，这种构象转变的速率限制了亚硝基氧化物不可逆衰变的速率。

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