Interplay between steric and electronic factors in determining the strength of intramolecular N—H...O resonance-assisted hydrogen bonds in β-enaminones
作者:Valerio Bertolasi、Loretta Pretto、Valeria Ferretti、Paola Gilli、Gastone Gilli
DOI:10.1107/s0108768106036421
日期:2006.12.1
compounds in order to establish which factors determine the range (2.53-2.72 A) of N...O hydrogen-bond distances in intramolecularly hydrogen-bonded beta-enaminones. It has been shown that, beyond electronic resonance-assisted hydrogen-bond effects modulated by substituents, the necessary requirements to produce very short N-H...O hydrogen bonding are steric intramolecular repulsions, including the embedding
报道了五个β-烯胺酮的晶体结构:(2Z)-3-(苄氨基)-1,3-二苯基-丙-2-烯-1-酮,(2Z)-3-(苄氨基)-3-( 2-羟基苯基)-1-苯基-丙-2-烯-1-酮,(2Z)-3-(苄氨基)-3-(4-甲氧基苯基)-1-(3-硝基苯基)-丙-2-烯-1-一,2- 1-[([4-甲氧基苯基)氨基]亚乙基}环己烯-1,3-二酮和2- 1-[(3-甲氧基苯基)氨基]亚乙基}环己烯-1,3-二酮。分析该结构并将其与类似化合物的结构进行比较,以确定哪些因素决定了分子内氢键合β-烯胺酮中N ... O氢键距的范围(2.53-2.72 A)。研究表明,除了由取代基调节的电子共振辅助氢键效应外,产生非常短的NH ... O氢键的必要条件是空间分子内排斥,包括在脂肪族六元环中嵌入烯氨基CC或CN键。通过考虑结构特征,可以预期特定β-烯胺酮所采用的NH ... O氢键的强度。