![]() These motifs are designated as S(6) in the graph-set assignments. However, it was discussed that six-member rings closed by the O–H∙∙∙O hydrogen bonds occur most often, especially in crystal structures it was pointed out that such six-member rings are more stable than their five-member ring counterparts. The latter example of the o-chlorophenol refers to the five-member ring closed by the intramolecular O–H∙∙∙Cl hydrogen bond. Several examples of intraHB systems were discussed in this early study in o-chlorophenol the hydroxyl hydrogen is attached to the chlorine however, if the chlorine center is replaced by the methyl group, there is no intramolecular energetically stabilizing link. This was explained by the formation of intramolecular rings for the former species. The distinct properties were also observed between some 1,2 disubstituted benzenes and their 1,3 as well as 1,4 disubstituted counterparts. They found that these interactions are responsible for differences in physical properties between ortho-substituted phenols where they occur, and meta-substituted as well as para-substituted phenols where they are not observed. ![]() According to the monograph of Jeffrey, it seems that intraHBs were identified very early, in 1924, by Sidgwick and Callow. Special attention is often paid on the intramolecular hydrogen bond (hereafter often marked as intraHB). It is well known that the hydrogen bond interactions play a crucial role in numerous physical, chemical and biological processes. ![]()
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