In this paper, a DFT study of phenylacetylene and styrene interactions with different surfaces ({111}, {100}, edge and corner) of Pd cluster was performed. The results obtained show that the interaction of phenylacetylene with Pd{111} or Pd{100} surfaces is stronger than that of styrene, but on the edges of Pd the adsorption of styrene is more preferable. The results agree with experimental observations, namely, with the nanoparticle size effect in the PhA semihydrogenation on Pd catalysts.

The existence of linear relationships has been demonstrated between stretching frequencies of R—H, RO—H, CH3CON(R)—H and R—OX (X = H for alcohols and O for peroxy radicals) bonds and radical stabilization energies, Es(R·), of related radicals. The correlation equations of Es(R·) and R—H bond dissociation energies (BDE), D(R—H), with the above stretching frequencies were obtained. From the equations the D(R—H) values for different hydrocarbons were calculated and compared with the experimental data. The mean difference between calculated and experimental values for saturated hydrocarbons is 2.3 kJ mol−1. The greater differences for some unsaturated hydrocarbons are discussed and explained. The BDEs calculated from the D(R—H = f (ν) equations may be regarded as the best. The IR spectra of menthol, menadione, 3‐methylpent‐2‐en‐4‐yn‐1‐ol and retinol were recorded in solution and the Es(R·) values of the corresponding radicals and the D(R—H) values of the related C—H bonds in the parent hydrocarbons were estimated for the first time. It is also shown that the radical stabilization energy may be used to estimate the reactivity of organic compounds in free radical reactions. One may conclude that the stabilization energy of the radicals of many organic compounds could be estimated from the vibrational spectra. The Es(R·) itself is a useful quantity for predicting kinetic and spectral properties of organic compounds. Copyright © 2001 John Wiley & Sons, Ltd.

The autoxidation of various retinyl polyenes and carotenoids in chlorobenzene at 45 "C and in thin solid films on a support at room temperature was investigated. The compounds used were pcarotene, canthaxanthin, retinyl acetate, methyl (all-E)-retinoate, methyl (13Z)-retinoate, retinal, C,, ketone, /3-ionylidene acetaldehyde, $-ionone, /3-ionone and ethyl sorbate as a model compound. It was shown that the isomerization of polyenyl peroxy radicals occurs during autoxidation of all the compounds studied, excepting pionone. A kinetic scheme for the polyene autoxidation process was considered and analysed. The conditions under which the rate constants of elementary reactions may be determined were defined and the rate constants of propagation and termination reactions for different polyenes were evaluated. The disappearance and formation of different functional groups were monitored by the spectroscopic investigation of autoxidation of polyene solid films. Mechanisms of the initial stages of the process are proposed for different polyenes.

Autoxidation of the biologically active polyenes b-carotene, canthaxanthin, retinyl acetate, methyl retinoate, retinal and 3,7,11,11-tetramethyl-10,15-dioxo-2,4,6,8-hexadecatetraenal (diketoretinal) in solid amorphous films was investigated. The course of the process was followed by electronic and IR spectroscopy. The overall activation energies were obtained. It was shown that insertion in the polyene molecule of a carbonyl group conjugated with polyene chain results in a drastic decrease in the reactivity towards molecular oxygen. The results are discussed and explained on the basis of radical stabilization energy, E S (R Á ), as a driving force of the autoxidation process. Semiempirical AM1 calculations of DH f of some retinyl polyenes and polyenyl radicals were carried out and the C-H bond strengths and E S (R Á ) values of corresponding polyenyl radicals were evaluated. It was shown that the incorporation of a carbonyl group in the polyene results in a decrease in the overall autoxidation rate due to the decrease in both the initiation and propagation rates.

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