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Photoelectron‐Spectroscopic Characterization of 3,4‐Dimethyl‐2,4‐hexadienes
Author(s) -
Honegger Evi,
Zhongzhi Yang,
Heilbronner Edgar,
Doering William V. E.,
Schmidhauser John C,
Publication year - 1984
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19840670303
Subject(s) - chemistry , atomic orbital , conformational isomerism , crystallography , ionization energy , spectral line , internal rotation , molecular orbital , twist , ionization , electron diffraction , stereochemistry , electron , computational chemistry , diffraction , molecule , quantum mechanics , physics , organic chemistry , mechanical engineering , ion , geometry , mathematics , engineering
The He(Ia) photoelectron (PE) spectra of the ( E,E )‐, ( E,Z )‐ and ( Z,Z )‐isomers of the title compound have been recorded to obtain information about their conformation in the gas phase. For a valid correlation with the PE data of other dienes it is necessary to take the potentials V (φ) for internal rotation and the corresponding conformer population densities P (φ) into account, as well as the rather complicated way wy in which the π −1 ionization energy gap Δ I (φ) depends on the direct π‐orbital interaction and the long‐range ‘through‐space’ interaction between the semi‐localized methyl‐group orbitals and the π‐orbitals. These factors being taken into account, the mean twist angles, φ , compatible with the PE‐spectroscopic results are φ ( E,E ) ≈ O° ± 30°, φ ( E,Z ) ≈ 80° or 110° within ± 15°, and φ (Z,Z) ≈ 85° to 105°. These results are in rough agreement with electron diffraction data by Traetteberg [15], other spectroscopic results and, for the ( E, E )‐ and (Z,Z)‐isomers, internal rotation potentials V (φ) previously calculated by Roth [17]. On the other hand the potential V (φ) proposed for the ( E,Z )‐isomer does not seem to be compatible with our findings.