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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >O-H Bond Dissociation Enthalpies of Oximes: A Theoretical Assessment and Experimental Implications
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O-H Bond Dissociation Enthalpies of Oximes: A Theoretical Assessment and Experimental Implications

机译：肟的O-H键离解焓：理论评估和实验意义

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摘要

By using a multilayer composite ab initio method ONION-G3B3, we calculated O-H bond dissociation enthalpies (BDEs) of 58 oximes that were measured experimentally. Experimental BDEs derived from thermal decomposition kinetics and calorimetric measurements were found to be consistent with the theory. However, the electrochemical method was found to give questionably high BDEs possibly due to errors in the measurement of pK_a~'s or redox potentials. Subsequently, the performances of a variety of DFT functionals including B3LYP, B3P86, B3PW91, BHandH, BHandHLYP, BMK, PBE1PBE, MPW1KCIS, mPWPW91, MPW1B95, and MPW1K were tested to calculate oxime O-H BDEs, where ROBHandHLYP was found to be the most accurate. By using this method, we calculated O-H BDEs of over 140 oximes in a systematic fashion. All of the calculated O-H BDEs fell in the range from 76.8 to 89.8 kcal/mol. An amino group on the azomethine carbon was found to strengthen the O-H bond, whereas bulky alkyl substituents on oximes decreased O-H BDEs due to their large steric-strain-relieving effects in the process of O-H bond cleavage. Para substituents had little effect on the BDEs of benzaldoximes and phenyl methyl ketoximes. Finally, on the basis of a spin distribution calculation, aryl-, alkyl-, and carbonyl-substituted iminoxyl radicals were found to be oradicals, whereas amino-substituted iminoxyl radicals were of pi-structure.
机译：通过使用多层复合从头计算方法ONION-G3B3，我们计算了58种肟的O-H键离解焓（BDE），这些是通过实验测得的。发现由热分解动力学和量热法测量得出的实验性BDE与理论相符。然而，发现电化学方法可能由于pK_a_或氧化还原电势的测量误差而产生可疑的高BDE。随后，测试了各种DFT功能的性能，包括B3LYP，B3P86，B3PW91，BHandH，BHandHLYP，BMK，PBE1PBE，MPW1KCIS，mPWPW91，MPW1B95和MPW1K的性能，以计算肟OH BDE，其中发现ROBHandHLYP最准确。通过使用这种方法，我们以系统的方式计算了140多种肟的O-H BDE。所有计算出的O-H BDEs均在76.8至89.8 kcal / mol的范围内。发现偶氮甲碱碳上的氨基增强了O-H键​​，而肟上的庞大烷基取代基则由于O-H键断裂过程中的巨大空间应变消除作用而降低了O-H BDEs。对位取代基对苯并肟和苯甲基酮肟的BDE几乎没有影响。最终，基于自旋分布计算，发现芳基，烷基和羰基取代的亚氨基氧基为芳烃，而氨基取代的亚氨基氧基为π-结构。

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