Focal Point Evaluation of Energies for Tautomers and Isomers for 3-Hydroxy-2-Butenamide: Evaluation of Competing Internal Hydrogen Bonds of Types -OH…O=, -OH…N, -NH…O=, and CH…X (X=O and N).

Zikri Altun,Erdi Ata Bleda,Carl Trindle

doi:10.3390/molecules26092623

Zikri Altun, Erdi Ata Bleda + Show 1 more

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https://doi.org/10.3390/molecules26092623

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Abstract

The title compound is a small molecule with many structural variations; it can illustrate a variety of internal hydrogen bonds, among other noncovalent interactions. Here we examine structures displaying hydrogen bonding between carbonyl oxygen and hydroxyl H; between carbonyl oxygen and amino H; hydroxyl H and amino N; hydroxyl O and amino H. We also consider H-bonding in its tautomer 2-oxopropanamide. By extrapolation algorithms applied to Hartree-Fock and correlation energies as estimated in HF, MP2, and CCSD calculations using the cc-pVNZ correlation-consistent basis sets (N = 2, 3, and 4) we obtain reliable relative energies of the isomeric forms. Assuming that such energy differences may be attributed to the presence of the various types of hydrogen bonding, we attempt to infer relative strengths of types of H-bonding. The Atoms in Molecules theory of Bader and the Local Vibrational Modes analysis of Cremer and Kraka are applied to this task. Hydrogen bonds are ranked by relative strength as measured by local stretching force constants, with the stronger =O…HO- > NH…O= > -OH…N well separated from a cluster > NH…O= ≈ >NH…OH ≈ CH…O= of comparable and intermediate strength. Weaker but still significant interactions are of type CH…N which is stronger than CH…OH.

Highlights

The concept of hydrogen bonding has evolved considerably over its century of history [1,2]
H bonding has been recognized as a primarily electrostatic phenomenon expressed by its effect on vibrational frequencies, molecular structure, and characteristic NMR parameters to mention the most prominent
We define the systems under study, describe the extrapolation techniques by which we obtain accurate relative energies, and lay out results of atoms in molecules (AIM) analy

Summary

Introduction

The concept of hydrogen bonding has evolved considerably over its century of history [1,2]. The anomalous properties of water prompted the first suspicion of an attractive interaction between a hydrogen atom in one water molecule with the oxygen of another Similar phenomena involving N and F were soon recognized as well. H bonding has been recognized as a primarily electrostatic phenomenon expressed by its effect on vibrational frequencies (most often red-shifting the OH stretch), molecular structure The concept of H bonding has been expanded from its original context so to include a number of surprising interactions, involving atoms other than oxygen, fluorine, and nitrogen [3,4]; “strong” H-bonding [5]; and “anomalous” (blue-shifting) H bonding [6]. Further expansion of the concept has been recognized [7]

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