Intramolecular Hydrogen Bond Energy and Its Decomposition—O–H∙∙∙O Interactions

Sławomir Grabowski

doi:10.3390/cryst11010005

Abstract

The method to calculate the energy of intramolecular hydrogen bond is proposed and tested for a sample of malonaldehyde and its fluorine derivatives; the corresponding calculations were performed at the ωB97XD/aug-cc-pVTZ level. This method based on relationships found for related intermolecular hydrogen bonds is compared with other approaches which may be applied to estimate the intramolecular hydrogen bond energy. Particularly, methods based on the comparison of the system that contains the intramolecular hydrogen bond compared with corresponding conformations where such interaction does not occur are discussed. The function-based energy decomposition analysis, FB-EDA, of the intramolecular hydrogen bonds is also proposed here.

Highlights

Several examples of intraHB systems were discussed in this early study; in o-chlorophenol the hydroxyl hydrogen is attached to the chlorine; if the chlorine center is replaced by the methyl group, there is no intramolecular energetically stabilizing link
The malonaldehyde species (Scheme 1) and its simple fluorine derivatives that are often classified as the resonance assisted hydrogen bonds, resonance-assisted hydrogen bonds (RAHBs) [9,10], are discussed in this study
The method to evaluate the energy of intramolecular hydrogen bond has been proposed; it may be described as the use of relationships known for related intermolecular hydrogen bonds that are applied to the intramolecular interactions where such energy cannot be calculated directly; this procedure may be classified as the function-based approach (FBA) [49]

Summary

Introduction

According to the monograph of Jeffrey [2], it seems that intraHBs were identified very early, in 1924, by Sidgwick and Callow [3]. They found that these interactions are responsible for differences in physical properties between ortho-substituted phenols where they occur, and metasubstituted as well as para-substituted phenols where they are not observed. The distinct properties were observed between some 1,2 disubstituted benzenes and their 1,3 as well as 1,4 disubstituted counterparts This was explained by the formation of intramolecular rings for the former species [3].

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Conclusion