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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Resonance-assisted hydrogen bonds: A critical examination. Structure and stability of the enols of beta-diketones and beta-enaminones
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Resonance-assisted hydrogen bonds: A critical examination. Structure and stability of the enols of beta-diketones and beta-enaminones

机译：共振辅助氢键：一项严格的检查。 β-二酮和β-烯胺酮的烯醇的结构和稳定性

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摘要

The characteristics of the intramolecular hydrogen bond (IMHB) for a series of 40 different enols of beta-diketones and their nitrogen counterparts have been systematically analyzed at the B3LYP/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) level of theory. In some cases, two tautomers may exist which are interconnected by a hydrogen shift through the IMHB. In tautomer a the HB donor group (YH) is attached to the six-membered ring, while in tautomer b the HB acceptor (X) is the one that is attached to the six-membered ring. We found that changing an O to a N favors the a tautomer when the atom is endo and the contrary when it is exo, while the presence of a double bond favors the a tautomers. As expected, the OH group behaves as a better HB donor than the NH2 group and the CNH group as a better HB acceptor than the CO group, although the first effect clearly dominates. Accordingly, the expected IMHB strength follows the [donor, acceptor] trend: [OH, CNH] > [OH, CO] > [NH2, CNH] > [NH2, CO]. For all those compounds in which the functionality exhibiting the IMHB is unsaturated (I-type), the IMHB is much stronger than in their saturated counterparts (II-type). However, when the systems of the II-type subset, which are saturated, are constrained to have the HB donor and the HB acceptor lying in the same plane and at the same distance as in the corresponding unsaturated analogue, the IMHB is of similar or even larger strength. Hence, we conclude that, at least for this series of unsaturated compounds, the resonance-assisted hydrogen bond effect is not the primary reason behind the strength of their IMHBs, which is simply a consequence of the structure of the sigma-skeleton of the system that keeps the HB donor and the HB acceptor coplanar and closer to each other.
机译：在B3LYP / 6-311 + G（3df，2p）// B3LYP / 6-311系统分析了一系列40种不同的β-二酮烯醇及其氮对应物的分子内氢键（IMHB）的特征。 + G（d，p）的理论水平。在某些情况下，可能存在两个互变异构体，它们通过通过IMHB的氢转移相互连接。在互变异构体a中，HB供体基团（YH）与六元环相连，而在互变异构体b中，HB受体（X）与六元环相连。我们发现，当原子为内向时，将O变为N有利于互变异构体，而当其为外向时则相反;而双键的存在则有利于互变异构体。如预期的那样，尽管第一个作用明显占优势，但OH基团的行为优于NH2基团，而HBN受体的行为优于NH2基团。因此，预期的IMHB强度遵循[供体，受体]趋势：[OH，CNH]> [OH，CO]> [NH2，CNH]> [NH2，CO]。对于所有表现出IMHB官能度不饱和的化合物（I型），IMHB比其饱和对应物（II型）强得多。但是，如果将饱和的II型子集的系统约束为使HB供体和HB受体与相应的不饱和类似物位于同一平面，并且位于相同的距离，则IMHB具有相似或更大的力量。因此，我们得出结论，至少对于这一系列不饱和化合物，共振辅助氢键效应不是其IMHBs强度背后的主要原因，这仅仅是系统sigma骨架结构的结果。使HB供体和HB受体保持共面且彼此靠近。

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