CH<sub>3</sub>···O Hydrogen Bond. Implications of Its Presence from the Substituent Effects on the Populations of Rotamers in 4-Substituted 9-Ethyl-1-methoxytriptycenes and 9-(Substituted Phenoxymethyl)-1,4-dimethyltriptycenes
作者:Yoshio Tamura、Gaku Yamamoto、Michinori Oki
DOI:10.1246/bcsj.60.1781
日期:1987.5
In the series of 4-substituted 9-ethyl-1-methoxytriptycenes, the populations of the sc conformer increase as the electron-density on the 1-methoxy–oxygen decreases. This trend was interpreted on the basis of steric repulsion which should increase as the electron density on the oxygen atom becomes high. In contrast, in the series of 9-(substituted phenoxymethyl)-1,4-dimethyltriptycenes, the high electron density on the aryloxy–oxygen favors the sc form. The stabilization of the sc form relative to the ap in the high electron density compounds in the latter series is attributed to the presence of CH3···O hydrogen bond, since other factors like Coulombic interactions, van der Waals repulsions, and van der Waals attractions could be excluded from being the main factor for the stabilization.
在系列的4-取代9-乙基-1-甲氧基三闭环化合物中,随着1-甲氧基氧原子的电子密度降低,sc构象的比例增加。这一趋势被解释为立体排斥作用,随着氧原子上电子密度的增加而增强。相反,在9-(取代苯氧基甲基)-1,4-二甲基三闭环化合物系列中,芳氧氧原子的高电子密度有利于sc形式。后者系列中,sc形式相对于ap形式的稳定性提高归因于CH3···O氢键的存在,因为其他因素如库仑相互作用、范德华排斥和范德华吸引力可以被排除为主要的稳定因素。