Conformationally Induced Changes in the Electronic Structures of Some Flexible Benzenes. A Molecular Orbital Model
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- 作者：R. T. Kroemer ; K. R. Liedl ; J. A. Dickinson ; E. G. Robertson ; J. P. Simons ; D. R. Borst ; and D. W. Pratt
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：December 9, 1998
- 年：1998
- 卷：120
- 期：48
- 页码：12573 - 12582
- 全文大小：262K
- 年卷期：v.120,no.48(December 9, 1998)
- ISSN：1520-5126
文摘
High-resolution electronic spectroscopy experiments on several substituted benzenes in the gas phasehave revealed a remarkable sensitivity of the orientation of the S1-S0 transition moment (TM) in the molecularframe to the conformation of the attached group. Here, we explore the origins of this effect by performing abinitio calculations on five conformationally flexible benzenes (toluene, ethylbenzene, n-propylbenzene,2-phenethyl alcohol, and 3-phenylpropionic acid) using the configuration interaction singles method (6-31G*basis set). Comparisons of the theoretical predictions with the experimentally determined parameters showthat there are two principal sources of the observed sensitivity: a "through-bond" effect caused by rotation ofthe substituent about the bond connecting it to the ring, which breaks the Cs symmetry of the parent molecule,and a "through-space" effect, apparently caused by interactions of the side chain orbitals with the 
orbitalsof the ring. "Purely electrostatic" interactions between the ring and the tail, while significant in some cases,result in TM orientations that do not agree with experiment. All three types of interactions produce mixingsof the ring * orbitals, which in turn can lead to 1La/1Lb excited electronic state mixing in the isolated molecule.Possible photochemical and photophysical consequences of this effect are discussed.
orbitalsof the ring. "Purely electrostatic" interactions between the ring and the tail, while significant in some cases,result in TM orientations that do not agree with experiment. All three types of interactions produce mixingsof the ring * orbitals, which in turn can lead to 1La/1Lb excited electronic state mixing in the isolated molecule.Possible photochemical and photophysical consequences of this effect are discussed.