As a test for the applicability of the density functional theory to the system containing intramolecular hydrogen bonds, calculations were performed on propen-1,2,3-triol, the feasible intermediate in the epimerization of dihydroxyacetone and glyceraldehyde enantiomers. A comparison is made between results obtained by Becke's three parameter hybrid functional (for exchange) with gradient corrections provided by the LYP correlation functional (B3LYP) and those predicted at the ab initio Møller−Plesset second-order (MP2) level. The calculated minimum energy structures are in excellent agreement with respect to both energy and geometries of hydrogen-bonded structures. Earlier and recent studies suggest that, generally, the nonlocal B3LYP approximation leads to a very accurate overall description of intramolecular hydrogen-bonded systems. We propose a new, more efficient computational protocol, which may be useful in the study of the biologically important molecules at a level of accuracy usually only provided by traditional post-Hartree−Fock ab initio methods.

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Among the conformers of the title compounds, all stable structures found reveal hydrogen bonding to an sp2 oxygen atom in five- or six-membered rings and usually cooperative effects. Nonlocal density functional calculations using different functionals prove the applicability of DFT to study geometries of systems containing intramolecular hydrogen bonds. The hydrogen bond parameters obtained applying the B3LYP approximation exhibit perfect agreement with those calculated at the MP2 level. The local gradient correction does not provide encouraging results.

Background: Molecular mechanics (MM) and quantum chemical (QM) calculations are widely applied and powerful tools for the stereochemical and conformational investigations of molecules. The same methods have been extensively used to probe the conformational profile of Taxol ( Figure 1) both in solution and at the β-tubulin protein binding site.

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