(He 1) photoelectron spectra of vinyl- and (1-dimethylaminovinyl)pyridines

Abstract

The (He 1) photoelectron spectra of α-, β-, γ-vinyl, α-, β-, and γ-(1-dimethylvinyl)-pyridines, 1-dimethyl- and 1-diethylaminostyrenes were obtained and interpreted within the framework of the molecular orbital perturbation theory. In both pyridine derivative series, there is a regular increase in the ionization energy of the 1a ₂, ^πC=C and n_en orbitals and decrease in the ionization energy of the 2b₁ orbitals in the order α < β < γ (inversion of orbitals 1a ₂ and 2b₁ is found for γ-vinylpyridine). The splitting of the energy levels of the heterocycle in dimethylaminovinylpyridines is less than in the corresponding vinyl derivatives, which indicates a weakening of the interaction between the aromatic (or heteroaromatic) ring and the enamine fragment extruding from the ring plane. The ionization energy of the unshared electron pair of the nitrogen atom of the pyridine ring for all the compounds except for α-(1-dimethylaminovinyl)pyridine (which displays an ortho effect) is close to that for pyridine. The photoelectron spectral data are compared with the MO energies calculated by the MINDO/3 method.