Photoelectron-Spectroscopic Characterization of 3,4-Dimethyl-2,4-hexadienes

✍ Scribed by Evi Honegger; Yang Zhong-zhi; Edgar Heilbronner; William V. E. Doering; John C; Schmidhauser

• Publisher: John Wiley and Sons
• Year: 1984
• Tongue: German
• Weight: 709 KB
• Volume: 67
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19840670303

✦ Synopsis

Abstract

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.