B3LYP and MP2 calculations of the enthalpies of hydrogen-bonded complexes of methanol with neutral bases and anions: comparison with experimental data.
To perfect a method for building a theoretical hydrogen-bond basicity scale, the enthalpy of hydrogen bonding between methanol and thirteen neutral and anionic bases (MeOH, MeNH2, Me2NH, Et2NH, Me3N, Et3N, Br-, CN-, SH-, Cl-, HCOO-, MeO-, F-) was calculated by DFT and ab initio methods. The theoretical results were compared to selected experimental ones. It appears that B3LYP/6-31+G(d,p) calculations are satisfactory for optimizing the geometry of complexes and giving a general order of basicity. However, they are deficient for reproducing the large effect of alkyl groups on the hydrogen-bond basicity of amines. This deficiency is explained by intermolecular perturbation theory calculations, which show that the alkylation of nitrogen dramatically increases the dispersion energy component not taken into account by the B3LYP functional. Of the methods considered, only MP2/aug-cc-pVTZ calculations are capable of reproducing the binding enthalpy within the experimental error for the first-row acceptor atoms N, O, and F, and of accounting for dispersion effects created by alkylation at the hydrogen-bond acceptor site.
Koné
Mawa
M
Laboratoire de Spectrochimie et Modélisation, EA 1149, FR CNRS 2465, Université de Nantes, 2 rue de la Houssinière, BP 92208, F-44322 Nantes Cedex 3, France.
Illien
Bertrand
B
Graton
Jérôme
J
Laurence
Christian
C
D000588:Amines / Q000737:chemistry* / Q000378:metabolism; D000838:Anions / Q000737:chemistry*; D006860:Hydrogen Bonding; D046911:Macromolecular Substances / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011789:Quantum Theory; D013816:Thermodynamics
D000588:Amines; D000838:Anions; D046911:Macromolecular Substances; D000432:Methanol