Rotational Barrier and Quantification of Electron-Donating Substituent Effects: a Computational Study of para-Substituted Benzaldehydes

IF 0.7 4区 化学 Q4 CHEMISTRY, MULTIDISCIPLINARY Croatica Chemica Acta Pub Date : 2020-10-11 DOI:10.5562/cca3672
Ali Hussain Yateem
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引用次数: 1

Abstract

The rotational barrier around the phenyl-formyl bond between the minimum and transition states of para-substituted benzaldehydes was computationally studied for 34 electron-donating substituents. The rotational barrier exhibited very good correlation with shortening of the phenyl-formyl bond, lengthening of carbonyl bond, increase of electron density at the formyl group, increase of stabilization energy, lowering of chemical shift in the 13C NMR of the formyl carbon, and with the values of empirical Hammett σp+ constants. Therefore, rotational barrier is a useful quantum mechanical parameter for quantifying the electron-donating substituent effect and π-conjugation in parasubstituted benzaldehydes. Based upon the rotational barrier a scale has been set in this work to judge the electron donating effect of substituents. Moreover, a canonical structure has been proposed for stronger electron-donating substituents. The results of this study reveal that simultaneous presence of electron acceptor formyl group and electron-donating groups is mandatory for the extension of resonance stabilization.
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给电子取代基效应的旋转势垒和量化:对取代苯甲醛的计算研究
计算研究了34个给电子取代基在对取代苯甲醛的最小态和过渡态之间围绕苯基甲酰基键的旋转势垒。旋转势垒与苯基-甲酰基键的缩短、羰基键的延长、甲酰基电子密度的增加、稳定能的增加、甲酰基碳的13C NMR中化学位移的降低以及经验Hammettσp+常数的值表现出非常好的相关性。因此,旋转势垒是定量准取代苯甲醛中给电子取代基效应和π-共轭的一个有用的量子力学参数。基于旋转势垒,本文建立了一个尺度来判断取代基的给电子效应。此外,对于更强的给电子取代基,已经提出了一种正则结构。本研究的结果表明,同时存在电子受体甲酰基和给电子基团对于延长共振稳定性是强制性的。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Croatica Chemica Acta
Croatica Chemica Acta 化学-化学综合
CiteScore
0.60
自引率
0.00%
发文量
3
审稿时长
18 months
期刊介绍: Croatica Chemica Acta (Croat. Chem. Acta, CCA), is an international journal of the Croatian Chemical Society publishing scientific articles of general interest to chemistry.
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