The present communication reports the results of a quantum mechanical study concerning stable conformations of 3-hexylthiophene and hexylbenzene molecules relative to the two side chain dihedral angles adjacent to the aromatic ring. In particular MP2, CCSD(T) and DFT calculations were performed in conjunction with standard basis sets. The results evidence a higher stability of selected gauche conformers of the side chain with respect to the anti arrangement. In particular, the 3-hexylthiophene system displays two different gauche conformers, one of which represents the absolute minimum. Both alkylaromatic fragments show similar potential energy surfaces characterized by the inverted stability of gauche and anti conformers with respect to n-hexane. Contrary to what previously assumed, we suggest that the prevalence of anti conformations in the crystal structures of alkylthiophenes can be ascribed to packing effects. The role of intramolecular CH/ interactions is important for the rationalization of the observed conformational preferences.
Unexpected Inversion in Preferential Stability of Gauche Over Anti Conformers of Alkylaromatics’Side Chains
FAMULARI, ANTONINO;BAGGIOLI, ALBERTO;MEILLE, STEFANO VALDO;RAOS, GUIDO
2012-01-01
Abstract
The present communication reports the results of a quantum mechanical study concerning stable conformations of 3-hexylthiophene and hexylbenzene molecules relative to the two side chain dihedral angles adjacent to the aromatic ring. In particular MP2, CCSD(T) and DFT calculations were performed in conjunction with standard basis sets. The results evidence a higher stability of selected gauche conformers of the side chain with respect to the anti arrangement. In particular, the 3-hexylthiophene system displays two different gauche conformers, one of which represents the absolute minimum. Both alkylaromatic fragments show similar potential energy surfaces characterized by the inverted stability of gauche and anti conformers with respect to n-hexane. Contrary to what previously assumed, we suggest that the prevalence of anti conformations in the crystal structures of alkylthiophenes can be ascribed to packing effects. The role of intramolecular CH/ interactions is important for the rationalization of the observed conformational preferences.File | Dimensione | Formato | |
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