"Amide resonance" correlates with a breadth of C-N rotation barriers
"Amide resonance" correlates with a breadth of C-N rotation barriers
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DOI：
10.1021/ja0663024
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发表时间：
2007-03-07
影响因子：
15
通讯作者：
Loewen, Mark J.
中科院分区：
文献类型：
--
作者：
Kemnitz, Carl R.;Loewen, Mark J.
采用完全基集计算方法（CBS-QB3）计算了乙酰胺及其8个相关化合物（包括乙酰胺烯酸酯和o -质子化乙酰胺）的CN旋转势垒。采用自然共振理论分析量化了酰胺共振对基态电子结构的贡献。一个旋转势垒的范围，跨越近50千卡/摩尔，与基态共振权值有很好的相关性，而不需要考虑过渡态的影响。使用合适的模型化合物对于理解在乙酰胺中CN键旋转过程中发生的结构和电子变化至关重要。不同的键长变化（δ rCO < δ rCN）与共振模型一致。同样，电荷差异与氮孤对电子给入羰基pi*轨道是一致的。尽管最近对共振模型的攻击，这些发现表明它是化学家武器库中一个复杂和高度预测的工具。
Complete basis set calculations (CBS-QB3) were used to compute the CN rotation barriers for acetamide and eight related compounds, including acetamide enolate and O-protonated acetamide. Natural resonance theory analysis was employed to quantify the "amide resonance" contribution to ground-state electronic structures. A range of rotation barriers, spanning nearly 50 kcal/mol, correlates well to the ground-state resonance weights without the need to account for transition-state effects. Use of appropriate model compounds is crucial to gain an understanding of the structural and electronic changes taking place during rotation of the CN bond in acetamide. The disparate changes in bond length (Delta rCO < Delta rCN) are found to be consonant with the resonance model. Similarly, charge differences are consistent with donation from the nitrogen lone pair electrons into the carbonyl pi* orbital. Despite recent attacks on the resonance model, these findings demonstrate it to be a sophisticated and highly predictive tool in the chemist's arsenal.