The electronic structures of 1H-benzotriazole and 19 of its 1-substituted derivs. were studied by UPS and quantum chem. methods. The conformational properties of some compds. were studied by semi-empirical and B3LYP calcns. For the alkenyl deriv. I a twisted conformation was ascertained both from IP values and calcns., and in the amino deriv. II the amino group is twisted by 90 Deg which is reflected by the absence of n/p interactions. With only a few exceptions, the ionization potentials corresponding to the 5 occupied p MOs (p1-p5) and the 2 n(N) orbitals of the 1H-benzotriazole unit (Bt1) could be detd. and assigned for all of the compds. Linear free energy correlations of the IPs related to these orbitals with inductive substituent parameters sI and F were satisfactory except for IP(p3). The energies of p and n MOs-except for p3-are thus affected primarily by the substituent's electronegativity. The different behavior of p3 is caused by direct interactions with substituent orbitals. For some substituents for which no sI or F parameters were known these could be detd. from their IPs by correlation anal.