N-protonation vs O-protonation in strained amides: Ab initio study
N-protonation vs O-protonation in strained amides: Ab initio study
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DOI：
10.1021/jo962063z
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发表时间：
1997-06-13
影响因子：
3.6
通讯作者：
Kim, KS
中科院分区：
文献类型：
--
作者：
Cho, SJ;Cui, CZ;Kim, KS
质子化在酰胺键水解中起着重要的催化作用。虽然酰胺的质子化位点仍有争议，但在普通酰胺中，O-质子化通常优于N-质子化。然而，N-质子化在应变分子系统中可能是有利的。为了系统地研究这种应变效应，我们研究了甲酰胺，应变N-甲酰氮杂环丁烷，和高应变N-甲酰氮杂环丁烷使用从头计算。电子相关效应被认为是重要的，在确定应变酰胺的质子化位点，因为它有助于稳定N-质子化略高于O-质子化。虽然O-质子化在N-甲酰基氮杂环丁烷和甲酰胺中是非常有利的，但在水相和气相中N-甲酰基氮杂环丁烷中N-质子化是有利的。在O-质子化的情况下，几何形状变得平坦，即使是高度紧张的酰胺。极性溶剂的存在有助于稳定N-质子化比O-质子化，平面性发现在O-质子化应变酰胺和非平面性在N-质子化应变酰胺将有一个重要的轴承在酶促反应以及在不对称合成。
Protonation plays an important catalytic role in amide bond hydrolysis. Although the protonation site of an amide is Still debatable, O-protonation is generally preferred to N-protonation in ordinary amides. However, N-protonation can be favored in strained molecular systems. To investigate this strain effect systematically, we studied formamide, strained N-formylazetidine, and highly strained N-formylaziridine using ab initio calculations. The electron correlation effect is found to be important in determining the protonation sites of strained amides, since it contributes to stabilize N-protonation somewhat more than O-protonation. Although O-protonation is highly favored in N-formylazetidine as well as in formamide, N-protonation is favored in N-formylaziridine in both aqueous and gas phases. In case of O-protonation, the geometries become planar even for highly strained amides. The presence of polar solvents contributes to stabilize N-protonation more than O-protonation, The planarity found in O-protonated strained amides and the nonplanarity in N-protonated strained amides would have an important bearing in enzymatic reactions as well as in asymmetric syntheses.