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Issue 4, 2008
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Regularities of the conformations on a single bond; sulfonic esters and sulfonyl derivatives

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Abstract

The so-called gauche rule preferring the less symmetrical sc conformations on sp3–sp3 bonds was revised by theoretical calculations of five sulfonyl derivatives: C6H5SO2OCH3, CH3SO2OC6H5, ClSO2OC6H5, C6H5SO2CH2Cl and C6H5SO2SO2C6H5. At the same time the limiting possibilities of common theoretical models were tested in predicting exact geometry and minute energy differences between rotamers. With a larger basis set, for instance at the level B3LYP/6-311+G(3df,3pd)//B3LYP/6-311+G(3df,3pd) or MP2/6-311+G(2df,2pd)//MP2/6-311+G(2df,2pd) different methods yielded concordant values of the dihedral angle τ characterizing the conformation. However, the predicted values of energy were not in sufficient agreement to give reliable population of rotamers. Probably the best estimate of this population can be obtained by combining the calculated angle τ with some experimental quantities, for instance with dipole moments. According to these results, the gauche rule is not a generally valid law. Preponderance of sc conformation in different classes of compounds may have different reasons. In our case, we obtained a qualitative explanation assuming that conformation is determined by destabilizing interaction of two polar bonds in the neighbouring sc position, while lone electron pairs have no observable effect.

Graphical abstract: Regularities of the conformations on a single bond; sulfonic esters and sulfonyl derivatives

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Publication details

The article was received on 20 Jun 2007, accepted on 13 Nov 2007 and first published on 29 Nov 2007


Article type: Paper
DOI: 10.1039/B709410H
New J. Chem., 2008,32, 638-642

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    Regularities of the conformations on a single bond; sulfonic esters and sulfonyl derivatives

    O. Exner and S. Böhm, New J. Chem., 2008, 32, 638
    DOI: 10.1039/B709410H

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