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Ring Rotation in Biphenyl by William Abbott

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... favor a planar conformation, the steric repulsion between the ortho-hydrogens ... Various methods were used to calculate ground state energies. ... – PowerPoint PPT presentation

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Title: 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
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