Quantum-chemical studies of ethyl fluoride: structure, scaled force fields and electrical properties

Abstract

Quantum-chemical (QC) calculations at HF, B3LYP and MP2 levels have been made for ethyl fluoride using the 6-311G ∗∗ basis. The B3LYP calculation was repeated with diffuse functions (6-311++G ∗∗). In the methyl group, the in-plane C–H bond is 0.002 Å longer than the out-of-plane one. QC force fields are scaled by refinement of fifteen independent scale factors to the frequencies of seven isotopic species. The B3LYP/6-311++G ∗∗ treatment accounts quantitatively for the α and β effects of fluorine substitution on isolated CH stretching frequencies ν isCH. Calculated centrifugal distortion constants agree well with observed values in most cases. Electrical properties of the atoms and bonds are described. The value is explored of the mean bending charge, p ⊥, defined as the mean of the terms p xx and p yy of the atomic polar tensor when the z axis lies along the bond concerned. In some situations, changes in p ⊥ follow variations in the Mulliken charge.