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

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Abstract
The structure and torsional barriers at 0° and 90° for biphenyl were studied by both ab initio and density functional methods by using various levels of theory with different basis sets. The torsional angle (φ) calculated at the MP2/6-311+G (2d,2p) level was 42.1°, while φ calculated using various density functionals with different basis sets was close to 40°. In contrast with the ab initio results, the torsional barrier at 0° [ΔE 0 =E(φ=0°)−E( equilibrium )] obtained using various density functionals coincided well with experimental values. The torsional barrier ratio (ΔE 90 /ΔE 0 ) obtained at the B3LYP/cc-pVTZ 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 (φ=19°) structure whereas its anionic counterpart has a planar structure. The ionization potential obtained at the B3LYP/6-311+G (2d,2p) level was 7.86 eV. Contrary to an earlier study, a positive electron affinity (EA) was obtained, in accordance with experimental predictions. EA values of 0.021 and 0.076 eV were obtained at the B3LYP/6-311+G (2d,2p) and B3LYP/aug-cc-pVDZ levels, respectively.