...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Importance of Electronic Delocalization on the C-N Bond Rotation in HCX(NH_2) (X = O, NH, CH_2, S, and Se)
【24h】

Importance of Electronic Delocalization on the C-N Bond Rotation in HCX(NH_2) (X = O, NH, CH_2, S, and Se)

机译：电子离域对HCX（NH_2）（X = O，NH，CH_2，S和Se）中C-N键旋转的重要性

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

A block-localized wave function method, which in effect can switch of conventional conjugation and hyperconjugation effects, is employed to investigate the origin of the rotational barriers in formamide and its analogues. It is found that the resonance between the π electrons on the C＝X double bond and the nitrogen lone pair significantly stabilizes the planar conformation in HCXNH_2 (X = O, NH, CH_2, S, and Se). The absolute resonance energy follows the order of formamide < thioformamide < selenoformamide, with predicted vertical resonance energies of -25.5, -35.7, and -37.6 kcal/mol, respectively. The computed vertical resonance energies for X = O, NH, and CH_2 are -25.5, -22.5, and -19.1 kcal/mol, respectively, which follow the decreasing trend of electrongegativity. Although the rotational barrier about the C-N bond in vinylamine (4.5 kcal/mol) is much smaller than that of formamide (15.7 kcal/mol), the resonance energy in vinylamine is of the same order as that of formamide (-19.1 versus -25.5 kcal/mol). Consequently, the rotational barrier in formamide cannot be simply regarded as a result of the carbonyl polarization as proposed in early studies. In fact, energy decomposition results reveal that resonance and σ-framework steric effects are equally important for the estimated difference in rotational barrier. Ab initio valence bond calculations are performed to investigate the electronic delocalization in formamide and its analogues. Examination of the electron density difference between the adiabatic (delocalized) and diabatic (localized) states revealed that the resonance in the planar formamide shifts electron density from nitrogen both to carbon and to oxygen, supporting the conventional resonance model. This is accompanied by the opposing migration of the σ charge density, making the integrated atomic charges smaller than that expected from pure π delocalization.
机译：实际上，可以切换常规共轭和超共轭效应的块局部波动函数法被用于研究甲酰胺及其类似物中旋转屏障的起源。发现C ＝ X双键上的π电子与氮孤对之间的共振显着稳定了HCXNH_2（X = O，NH，CH_2，S和Se）中的平面构象。绝对共振能遵循甲酰胺<硫代甲酰胺<硒甲酰胺的顺序，预测的垂直共振能分别为-25.5，-35.7和-37.6 kcal / mol。 X = O，NH和CH_2的垂直共振能的计算值分别为-25.5，-22.5和-19.1 kcal / mol，遵循电子负性的下降趋势。尽管乙烯胺中CN键的旋转势垒（4.5 kcal / mol）比甲酰胺（15.7 kcal / mol）小得多，但乙烯胺中的共振能与甲酰胺的共振能级相同（-19.1对-25.5） kcal / mol）。因此，不能像早期研究中提出的那样简单地认为甲酰胺中的旋转势垒是羰基极化的结果。实际上，能量分解结果表明，共振和σ框架空间效应对于旋转势垒的估计差异同样重要。从头计算价键计算是为了研究甲酰胺及其类似物中的电子离域。绝热（离域）和非绝热（局部）状态之间的电子密度差的检查表明，平面甲酰胺中的共振使电子密度从氮转移到碳和氧，从而支持了常规共振模型。伴随着σ电荷密度的相反迁移，使积分原子电荷比纯π离域化所期望的要小。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号