Phenyl rotation in diphenylether and diphenylmethane calculated with ab initio methods

Diphenylether 1 and diphenylmethane 2 are calculated as chiral C-2 symmetrical minimum structures (1A and 2A) by HF/6-31G(d), MP2/6-31G(d), BLYP/6-31G(d) and B3LYP/6-31G(d) ab initio and density functional computations. The complete torsional energy surface for the rotation of the phenyl rings in 1 and 2 is given (HF/6-31G(d)). The phenyl rings in diphenylether rotate preferably via a C-S symmetrical transition state 1C. The energy barrier for the process is very low (e.g. 0.30 kcal mol(-1) at the MP2 level). Diphenylmethane uses two transition states of low energy for ring flipping, 2B and 2C having C-2v and C-S symmetry (0.51 and 0.49 kcal mol(-1) above 2A at the MP2 calculations). The central C-O-C and C-CH2-C bending angles in 1 and 2, respectively, are strongly correlated with the dihedral angles of the ring torsion.