Structural chemistry of polycyclic heteroaromatic compounds. Part 10: photoelectron spectra and electronic structures of 1-substituted 1 H-benzotriazoles

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The electronic structures of 1 H-benzotriazole ( 1) and its 1-substituted derivatives 2– 20 have been investigated by ultraviolet photoelectron spectroscopy and quantum chemical methods. The conformational properties of some compounds were studied by semi-empirical and B3LYP calculations. For the alkenyl derivative 14 a twisted conformation was ascertained both from IP values and calculations, and in the amino derivative 20 the amino group is twisted by 90° which is reflected by the absence of n/π interactions. With only a few exceptions, the ionization potentials corresponding to the five occupied π MOs (π 1–π 5) and the two n(N) orbitals of the 1 H-benzotriazole unit (Bt 1) could be determined and assigned for 1– 20. Linear free energy correlations of the IPs related to these orbitals with inductive substituent parameters σ I and F were satisfactory except for IP(π 3). The energies of π and n MOs—except for π 3—are thus affected primarily by the substituent's electronegativity. The different behaviour of π 3 is caused by direct interactions with substituent orbitals. For some substituents for which no σ I or F parameters were known these could be determined from their IPs by correlation analysis.