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The first two ionization energy values of p-substituted trans-azobenzenes pX-C6H4-N = N-C6H5 (X = NH2, OCH3, OH, CH3, H, Cl, COOH and NO2) are reported. These have been obtained by U.V. (HeI and HeII) photoelectron spectroscopy (UPS). The substituent effect indicates that for electron donor substituents, the highest occupied orbital is π-type. This is confirmed by semiempirical calculations. When the substituent is H or a withdrawing group, the first two bands heavily overlap, and in these cases no certain assignment was possible, in spite of the several approaches used. The UPS data are discussed along with previous polarographic and U.V. absorption measurements.

The ultraviolet photoelectron spectra of [2,2](2,5)furanophane (FUPH) and [2,2](2,5)thiophenophane (THPH) have been analyzed on the basis of a perturbational molecular orbital analysis, by comparison with CNDO/2 computations and by correlating them with the spectra of related molecules. Through space and through bond interactions between the two heteroaromatic rings are shown to be important in determining the ordering of the outermost MO’s in this class of compounds.

The first two π(a2, b1) IE’s, of monosubstituted benzenes containing di- and tri-coordinated nitrogen directly linked to the ring have been measured and analysed together with the N1s IE. These photoelectron properties are found to respond in the same sense, though to different extents, to inductive and mesomeric interactions that the N-containing substituents sustain with the aromatic ring. The different sensitivities of these properties to substituent changes are discussed in connection with mechanisms of transmission of electronic effects with the aid of the ground state electronic structures determined by means of ab-initio calculations. The relative contribution of the relaxation energy to the considered core and valence IE’s is also examined by referring to the model used by Gelius and Siegbahn. The factors determining the apparently anomalous behaviour of nitrobenzene are discussed

The low ionization energy regions of the photoelectron (He I) spectra of several p-p′-substituted thiobenzophenones (X-C6H4)2CS and of the corresponding S-oxides (sulphines) (XC6H4)2CSO (where X = H , OCH3, CH3, I, Br, Cl and NO2) have been assigned on the basis of perturbational molecular orbital theory arguments coupled with CNDO/2 computations and substituent effects. For the thioketones, the ordering of the outermost MO's results to be n(S), π7, π6, π5/π4, π3, n(S) being the HOMO; while for the sulphines the two outermost MO’s have π character and correspond to π7 and π6 in the thioketones. In the light of the above results the different behaviour toward oxidation of these two classes of compounds can be rationalized.

Since the first electron spectroscopic (ESCA) studies dealing with substituents effects upon core ionization energies (I.E.) of organic compounds1, little has been published on the subject. This was probably because the reported data did not always seem very meaningful. The absolute I.E. values obtainable in the solid phase are not very certain and also, the "shake-up" phenomena and the consequent broadening of the bands, which affect the I.E. values2, were not always taken into account. None the less we think that ESCA is a valuable tool for the study of substituent effects, and in particular of the transmission of electronic effects in aromatic systems. Previous work in this area has been published 2,3 , and more specifically an example of steric inhibition of resonance observed by means of ESCA I.E.'s and shake up data was recently reported4. Here we would like to report a further case in which the transmission of electronic effects through an aromatic ring is observed using ESCA.