Nonbonding pairs in cyclic thioethers: Electrostatic modelling and ab initio calculations for complexes of 2,5-dihydrothiophene, thietane and thiirane with hydrogen fluoride

Electrostatic potential energies V(ϕ) of a non‐perturbing, protonic charge at fixed distances r from the S atom in three cyclic thioethers were examined as functions of the angles ϕ made by the r‐vector with the C2 axis (thiirane and 2,5‐dihydrothiophene) or the local C2 axis (thietane). The electrostatic PE VHF(ϕ) of HF (HF modelled as an extended electric dipole) was also calculated and the results compared with geometries of the thioether⋯HF complexes calculated at the CCSD(T)‐F12c/cc‐pVTZ‐F12 level. The latter reveal angular deviations θ ∼10‐20° of the S⋯H-F nuclei from collinearity in directions suggesting secondary interactions of F with H atom(s) of the rings. Angles ϕ made by the S⋯H hydrogen bond with the C2 (or local C2) axes in the complexes are systematically larger (∼4‐9°) than indicated by the VHF(ϕ) functions. Minima in the simple V(ϕ) versus ϕ functions occur at values smaller (∼5‐10°) than those in the VHF(ϕ) curves.