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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.

The dipole moments of di-2-pyridyl dichalcogenides in benzene solution at 25 and 45° and the HeI photoelectron spectra of di-2-pyridyl and diphenyl dichalcogenides R2X2(X = S, Se, or Te) were investigated to obtain information about the conformation of these molecules in solution and in the gas phase. The calculated C–X–X–C dihedral angles (100–110°) for the dipyridyl dichalcogenides, for which µcalc=µexp, are at least 10° larger than those for the diphenyl derivatives. These results indicate that the π-interactions between the X atoms and the pyridyl groups are more effective than between the X atoms and the phenyl rings, reducing, as a consequence, repulsion between the lone electron pairs of the chalcogen (X) atoms and lowering the torsional barriers about the X–X bonds. The variation of the dihedral angles between the phenyl derivatives and the corresponding dipyridyl dichalcogenides as derived on the basis of photoelectron spectroscopic data, is in disagreement with the results from dipole moment data. This difference between the gas phase and solution results may be caused by solvent and temperature effects or by secondary interactions between the π and σ orbitals. The dipole moment and photo-electron spectral data indicate that the diaryl dichalcogenides are conformationally flexible with a skew equilibrium conformation and very little interaction between the two aryl groups.

For organometallic sulphides p-Me3XC6H4SMe (I), p-Me3XCH2C6H4 SMe (II), and PhSCH2XMe3(III)(X = Si, Ge. Sn, or Pb) the oxidation rates with perbenzoic acid have been measured spectrophotometrically at 25° and compared with the ionization energies obtained by u.v. photoelectron spectroscopy measurements. From the results obtained for sulphides (I), +I, (p→d)π and hyperconjugative contributions almost cancel out; for series (II) and (III) however the electron-releasing character of the CH2XMe3 group confirms the importance of C-metal hyperconjugation. Solvent effects on the oxidation rates of the title compounds have also been studied and are discussed in detail.

Phenyl isocyanate attacks both the morpholine and the pyrrolidine enamine derived from 2-tetralone at C-1, whereas β-nitrostyrene attacks the former 80% at C-1 and 20% at C-3 and the latter exclusively at C-3. These results confirm the existence of an equilibrium between the 3,4- and 1,4-dihydro-forms of the enamines.

The ionization energy (i.e.) values for electrons in the π MOs of some tertiary amines and enemines derived from morpholine, piperidine and pyrrolidine have been determined by u.v. photoelectron spectroscopy. The effects of structural changes are discussed. The nitrogen lone pair i.e. value is taken as a measure of basicity of amines and enamines in the gas phase. The relative order of basicity is secondary amines < tertiary amines < enamines. This order differs from that found in aqueous solution probably because of solvation effects in the latter.

10,10-Dimethylphenothia-silin and -germin have been prepared for the first time and their properties compared with those of the corresponding tin derivative and of 9,9-dimethyithioxanthen. The 13C n.m.r. spectra of these compounds suggest increasing strain in the heterocyclic framework on going down Group IVB. The oxidation rates of sulphur to sulphinyl group with perbenzoic acid have been measured in carbon tetrachloride. The first few bands in the photoelectron (HeI) spectra are assigned by comparison with the spectra of related compounds. The reactivity sequence and the ionization energy data indicate that, for geometrical changes along the series, the interaction between the sulphur lone pair and the benzene rings decreases on going towards the Sn derivative.

The presence of an anomalous band at 12.1 eV in the u.v. photoelectron spectrum of quinolinimide when compared with those of N-methylquinolinimide, phthalimide, and N-methylphthalimide is explained as being due to a tautomeric form of quinolinimide different from that in the other compounds. This conclusion is supported by results obtained from X-ray photoelectron measurements. I.r. and 1H n.m.r. evidence also confirms the existence of a form with strong hydrogen bonding

The ultraviolet photoelectron spectra (UPS) of several furyl- and thienyl-mercury derivatives have been recorded. The analysis of the furan-like π2 and π3 molecular orbitals (MOs) indicated that in bis-2-furylmercury there is a small charge-transfer interaction between the filled ring π orbitals and the empty 6pπ mercury atomic orbitals, that this interaction is larger than in the corresponding bis-3-furyl derivative, and, for both compounds, larger than the interaction with the 5d atomic orbitals of mercury. This conclusion is supported by X-ray photoelectron spectral (XPS) data and iterative extended Huckel MO (IEHMO) calculations, and applies equally well to the corresponding thiophen derivatives. The electron-releasing inductive effect of mercury, in these compounds, turned out to be similar to or slightly larger than that of a methyl group. The CH2HgCl substituent exerts a hyperconjugative destabilization on the ring π2 and π3 MOs via the C–Hg σ bond. This effect is, however, smaller than that exerted on benzene and ethylene. The HgCl substituent was found to be slightly electron-withdrawing.

Half-wave oxidation potentials (E1/2), in acetonitrile at a platinum electrode, and gas-phase ionization potentials (P) have been measured for a number of indole and indolizine derivatives, variously substituted on the five-membered ring. Except for a few compounds, a linear correlation of P vs. E1/2 was found. Deviations from linearity are discussed in terms of conformation differences between the two phases and P value uncertainties in those cases where the vibrational fine structure was resolved.