Abstract
The electronic structures of 1H-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 degrees which is reflected by the absence of n/pi interactions. With only a few exceptions, the ionization potentials corresponding to the five occupied pi MOs (pi(1)-pi(5)) and the two n(N) orbitals of the 1H-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 sigma(1) and F were satisfactory except for LP(pi(3)). The energies of pi and n MOs-except for pi(3)-are thus affected primarily by the substituent's electronegativity. The different behaviour of pi(3) is caused by direct interactions with substituent orbitals. For some substituents for which no sigma(1) or F parameters were known these could be determined from their IPs by correlation analysis. (C) 1999 Elsevier Science B.V. All rights reserved.