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Non-Covalent Interactions in Molecular Systems: Thermodynamic Evaluation of the Hydrogen-Bond Strength in Amino-Ethers and Amino-Alcohols
Authors:Riko Siewert  Dr. Kseniya V. Zherikova  Prof. Dr. Sergey P. Verevkin
Affiliation:1. Department of Physical Chemistry and Faculty of Interdisciplinary Research, Competence Centre CALOR, University of Rostock, 18059 Rostock, Germany;2. Nikolaev Institute of Inorganic Chemistry of Siberian Branch of Russian Academy of Sciences, 630090 Novosibirsk, Russia
Abstract:The intramolecular hydrogen bond (intra-HB) is one of the best-known examples of non-covalent interactions in molecules. Among the different types of intramolecular hydrogen bonding, the NH⋅⋅⋅O hydrogen bond in amino-alcohols and amino-ethers is one of the weakest. In contrast to the strong OH⋅⋅⋅N intramolecular hydrogen bond, the strength of the NH⋅⋅⋅O bond can hardly be measured with conventional spectroscopic methods, even for simple amino-alcohols, since the band belonging to the NH⋅⋅⋅O conformer merges with the free OH band. In this work, we developed a combination of G4 calculations, and a method based on experimental vaporization enthalpies to determine the NH⋅⋅⋅O hydrogen bonding strength. The archetypal compounds for this study are 2-amino-1-ethanol and 3-amino-1-propanol as well as their respective methoxy analogs. Based on these molecules, different series were studied to investigate various factors influencing NH⋅⋅⋅O intra-HB strength. In the first series, the influence of alkylation near the hydroxy or methoxy group and the amino group in sterically hindered aminoalcohols was examined. In the second series, the influence of alkylation of the amino-group was investigated. In the third series, the effect of extending the alkyl chain between functional groups was studied.
Keywords:enthalpy of formation  enthalpy of vaporization  intra-molecular hydrogen bonding  quantum-chemical calculations  structure-property relationships
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