Torsional barrier, ionization potential, and electron affinity of biphenyl- A theoretical study

The structure and torsional barriers at 0 degrees and 90 degrees for biphen yl were studied by both ab initio and density functional methods by using v arious levels of theory with different basis sets. The torsional angle (phi ) calculated at the MP2/6-311+G(2d,2p) level was 42.1 degrees, while phi ca lculated using various density functionals with different basis sets was cl ose to 40 degrees. In contrast with the ab initio results, the torsional ba rrier at 0 degrees [DeltaE(0)=E(phi =0 degrees)-E(equilibrium)] obtained us ing various density functionals coincided well with experimental values. Th e torsional barrier ratio (DeltaE(90)/DeltaE(0)) obtained at the B3LYP/cc-p VTZ level, 1.0988, agreed well with the experimental value, 1.0833, whereas it was 0.416 at the MP2/6-311G(d,p) level. Structural studies on biphenyl ions showed that the biphenyl cation has a nonplanar (phi =19 degrees) stru cture whereas its anionic counterpart has a planar structure. The ionizatio n potential obtained at the B3LYP/6-311+G(2d,2p) level was 7.86 eV. Contrar y to an earlier study, a positive electron affinity (EA) was obtained, in a ccordance with experimental predictions. EA values of 0.021 and 0.076 eV we re obtained at the B3LYP/6-311+G(2d,2p) and B3LYP/aug-cc-pVDZ levels, respe ctively. (C) 2001 American Institute of Physics.