THEORETICAL-STUDIES ON CIS-AMIDE PREFERENCE IN N-METHYLANILIDES
THEORETICAL-STUDIES ON CIS-AMIDE PREFERENCE IN N-METHYLANILIDES
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DOI：
10.1021/jo00120a011
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发表时间：
1995-07-28
影响因子：
3.6
通讯作者：
ITAI, A
中科院分区：
文献类型：
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作者：
SAITO, S;TORIUMI, Y;ITAI, A
通过乙酰苯胺和 N-甲基乙酰苯胺的从头计算分子轨道 (MO) 计算，研究了晶体和溶液中 N-甲基苯胺中顺式酰胺结构的已知一般偏好。 N-甲基乙酰苯胺中的顺式结构比反式结构稳定3.50 kcal/mol，而在6-31G**//4-31G基组水平上，性状结构比乙酰苯胺中的顺式结构稳定2.15 kcal/mol。为了检查结果的可靠性，还通过在N-甲基乙酰胺的情况下将基组从4-31G改变为6-31G**来检查反式和顺式酰胺结构之间的能量差的基组依赖性。 N-甲基苯胺中显着的顺式偏好似乎归因于反式结构的不稳定，这是由于两个甲基之间的空间位阻以及羰基孤对电子和扭曲苯基取向中的苯基π电子之间的电子排斥造成的。
The known general preference of cis-amide structure in N-methylanilides both in crystal and in solution was studied by ab initio molecular orbital (MO) calculations for acetanilide and N-methylacetanilide. The cis structure was more stable by 3.50 kcal/mol than the trans one in N-methylacetanilide, whereas the traits structure was more stable by 2.15 kcal/mol than the cis one in acetanilide at the 6-31G**//4-31G basis set level. In order to examine the reliability of the result, the basis set dependency of the energy difference between trans- and cis-amide structures was also examined by changing the basis set from 4-31G to 6-31G** in the case of N-methylacetamide. The remarkable cis preference in N-methylanilides seems to be ascribed to destabilization of the trans structure due to steric hindrance between the two methyl groups and to electronic repulsion between the carbonyl lone-pair electrons and the phenyl pi-electrons in the twisted phenyl orientation.