title: Importance of the Electron Correlation and Dispersion Corrections in Calculations Involving Enamines, Hemiaminals, and Aminals. Comparison of B3LYP, M06-2X, MP2, and CCSD Results with Experimental Data.
abstract: While B3LYP, M06-2X, and MP2 calculations predict the ΔG° values for exchange equilibria between enamines and ketones with similar acceptable accuracy, the M06-2X/6-311+G(d,p) and MP2/6-311+G(d,p) methods are required for enamine formation reactions (for example, for enamine 5a, arising from 3-methylbutanal and pyrrolidine). Stronger disagreement was observed when calculated energies of hemiaminals (N,O-acetals) and aminals (N,N-acetals) were compared with experimental equilibrium constants, which are reported here for the first time. Although it is known that the B3LYP method does not provide a good description of the London dispersion forces, while M06-2X and MP2 may overestimate them, it is shown here how large the gaps are and that at least single-point calculations at the CCSD(T)/6-31+G(d) level should be used for these reaction intermediates; CCSD(T)/6-31+G(d) and CCSD(T)/6-311+G(d,p) calculations afford ΔG° values in some cases quite close to MP2/6-311+G(d,p) while in others closer to M06-2X/6-311+G(d,p). The effect of solvents is similarly predicted by the SMD, CPCM, and IEFPCM approaches (with energy differences below 1 kcal/mol).
authors.affiliation: Departament de Química Orgànica, Facultat de Química, Universitat de Barcelona , Diagonal 645, 08028 Barcelona, Catalonia, Spain.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Castro-Alvarez
authors.affiliation: Departament de Química Orgànica, Facultat de Química, Universitat de Barcelona , Diagonal 645, 08028 Barcelona, Catalonia, Spain.
authors.forename: Héctor
authors.initials: H
authors.lastname: Carneros
authors.affiliation: Departament de Química Orgànica, Facultat de Química, Universitat de Barcelona , Diagonal 645, 08028 Barcelona, Catalonia, Spain.
authors.forename: Dani
authors.initials: D
authors.lastname: Sánchez
authors.affiliation: Departament de Química Orgànica, Facultat de Química, Universitat de Barcelona , Diagonal 645, 08028 Barcelona, Catalonia, Spain.
authors.forename: Jaume
authors.initials: J
authors.lastname: Vilarrasa