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Relationship between stereochemistry and charge density in hydrogen bonds with oxygen acceptors

机译：氧受体氢键的立体化学与电荷密度之间的关系

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An extensive survey of Cambridge Structural Database was carried out to study the directionality and stereochemistry of hydrogen bonds with an oxygen acceptor including carbonyl, alcohols, phenols, ethers, and esters groups. The results obtained through this survey are correlated with the charge density of these different chemical groups. The electron density of these different oxygen atom types shows striking dissimilarities in the electron lone pair configuration. Esters and ethers with the C-O-C oxygen atom located in an aromatic cycle display merged lone pairs lobes, which is not the case when one of the bonded carbon atoms has sp~3 hybridization. The positions of the lone pairs in the deformation electron density maps derived from theoretical calculation and from experimental charge density generally agree with the notable exception of phenols and C(sp~3) esters. The experimental studies show generally lone pairs lobes that are closer to each other. Differences are found within COH groups: the two electron lone pairs are slightly closer in phenol oxygen atoms compared with alcohols in theoretical electron densities. In experimental charge densities, the discrepancy is more drastic because the two lone pair lobes appear merged in phenols; this might be due to a resonance effect with the neighboring sp~2 carbon atom. This difference in the configuration of the two electron lone pairs affects the directionality of hydrogen bonds. For phenols, the preferred donor hydrogen atom position is close to the COH plane, while for alcohols, it is out of plane with the direction O?H_(donor) forming an angle of around 30 to the COH plane. The number of H-bonds occurring with the donor hydrogen atom pointing toward the middle of the two lone pairs is small for carbonyl, contrary to alcohols and phenols. Also H-bonds involving alcohol/phenol acceptors have a stronger tendency to occur in directions close to the electron lone pair plane than for carbonyl. As expected, the directional attraction of hydrogen bond donors toward the lone pairs is much more pronounced for short H?O distances. This study could have implications in the design of force fields, in molecular recognition, in supramolecular crystal engineering, and in drug design.
机译：对剑桥结构数据库进行了广泛的调查，以研究氢氧键与羰基，醇，酚，醚和酯基的氢键的方向性和立体化学。通过该调查获得的结果与这些不同化学基团的电荷密度相关。这些不同的氧原子类型的电子密度在电子孤对构型中显示出惊人的相似性。芳香环中带有C-O-C氧原子的酯和醚显示出合并的孤对叶，当键合的碳原子之一具有sp〜3杂化时则不是这样。从理论计算和实验电荷密度得出的变形电子密度图中孤对的位置通常与苯酚和C（sp〜3）酯显着不同。实验研究通常显示彼此靠近的孤对叶。在COH基团中发现差异：在理论电子密度上，两个孤电子对的苯酚氧原子与醇相比稍近。在实验电荷密度中，差异更明显，因为两个孤对叶似乎合并在酚中。这可能是由于与邻近的sp〜2碳原子的共振效应。两个电子孤对的构型的这种差异影响氢键的方向性。对于苯酚，优选的供体氢原子位置靠近COH平面，而对于醇，它不在平面内，方向O？H_（供体）与COH平面成30度角。与醇和酚相反，羰基的供体氢原子指向两个孤对的中间时发生的H键数目很少。与羰基相比，涉及醇/酚受体的氢键在靠近电子孤对平面的方向上更倾向于发生。如所预期的，对于短的H 2 O距离，氢键供体对孤对的定向吸引力要明显得多。这项研究可能对力场的设计，分子识别，超分子晶体工程和药物设计有影响。

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