Issue 39, 2009

Conformational properties of six-membered heterocycles: accurate relative energy differences with DFT, the importance of dispersion interactions and silicon substitution effects

Abstract

Density functional methods were evaluated in their ability to predict relative conformational energies of a test set of monosubstituted cyclohexanes and six-membered heterocycles. It is shown that while popular density functionals like B3LYP are unreliable for predicting accurate conformational energies for the axial/equatorial equilibrium of monosubstituted cyclohexanes, 1-silacyclohexanes and tetrahydropyrans, density functionals that take into account dispersion interactions like M06-2X and B2PLYP-D result in energy differences close to CCSD(T)/CBS results. Using the M06-2X density functional, we have then investigated the conformational properties of a large number of monosubstituted silacyclohexanes, with the number of silicon atoms ranging from 1 to 6. Our calculations suggest remarkably different conformational properties when compared to cyclohexane. The carbon/silicon exchange in a cyclohexane ring often has systematic, yet counterintuitive effects on the conformational properties. Dispersion interactions are shown to be especially important for accurate relative energy calculations of polysilacyclohexanes.

Graphical abstract: Conformational properties of six-membered heterocycles: accurate relative energy differences with DFT, the importance of dispersion interactions and silicon substitution effects

Supplementary files

Article information

Article type
Paper
Submitted
21 May 2009
Accepted
24 Jun 2009
First published
31 Jul 2009

Phys. Chem. Chem. Phys., 2009,11, 8689-8697

Conformational properties of six-membered heterocycles: accurate relative energy differences with DFT, the importance of dispersion interactions and silicon substitution effects

R. Bjornsson and I. Arnason, Phys. Chem. Chem. Phys., 2009, 11, 8689 DOI: 10.1039/B910016D

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