Ring Rotation in Biphenyl by William Abbott

1
Ring Rotation in Biphenylby William Abbott
2
Ground State Geometry

• While ?-electron delocalization effects would
  favor a planar conformation, the steric repulsion
  between the ortho-hydrogens would favor a
  staggered position.
• Torn between these two competing forces, one
  would expect the equilibrium twist angle to lie
  somewhere between 0 and 90.

3
Various methods were used to calculate ground
state energies.Only HF/6-31G produced a
conformational energy minimum which closely
corresponds with the gas-phase electron
diffraction results of 44.4 1,2
4
Excited State EnergyCalculations were performed
for the first excited singlet state. The results
indicate a near-planar conformational energy
minimum, which accords with indirect Raman
spectroscopy evidence3 and with the vibrational
structure of the fluorescence spectrum of
biphenyl in solution4.
5
Possible scheme for Fluorescence in Biphenyl
6
Ground State HOMO
7
References

• Almenningen, A. Bastiansen, O. Fernholt, L.
  Cyvin, B. N. Cyvin, S.J. Samdal, S. J. Mol.
  Struct. 1985, 128, 59.
• Bastiansen, O. Samdal, S. J. Mol. Struct. 1985,
  128, 115.
• Matsunuma, S. Yamaguchi, S. Hirosem C. Maeda,
  S. J. Phys. Chem. 1988, 92, 1777.
• Lim, E.C. Li, Y.H. J. Chem. Phys. 1970, 52, 6416