ESR AND QUANTUM-CHEMICAL STUDIES OF THE STRUCTURE AND THERMAL TRANSFORMATIONS OF VINYLCYCLOPROPANE RADICAL CATIONS IN IRRADIATED FROZEN FREON MATRICES - SIMULATION OF RADICAL PROCESSES IN THE GAS-PHASE

Thermal trasfomations of vinylcyclopropane (VCP) radical cations (RC) in X-ray irradiated frozen Freon matrices, CFCl2CF2Cl and CFCl3, were studed by ESR. Radical processes involving VCP.+ in very rarefied and moderately thickened gaseous VCP were simulated. Monomolecular cleavag e of the cyclopropane ring of gauche-VCP.+ (1) occurs to give the more thermally stable distonic radical cation dist(0.90)-C5H8.+ (3). As th e density of VCP increases RC 3 adds at the double bond of anti-VCP to give the distonic RC, (CH2CH2CHCH)-C-.(CH2)(3)CHCHCH2+ (5). Under the same conditions, the less thermally stable anti-VCP.+ (2) undergoes m onomolecular isomerization into RC 1 or reacts with anti-VCP with the rearrangement (as in the condensed phase) to give its distonic form, d ist(90.0)-C(5)H8(.+) (4). The MNDO-UHF method was adapted for quantum- chemical analysis of the constants of isotropic hyperfine coupling wit h H-1 and C-13 nuclei in neutral and charged hydrocabon radicals, sinc e the standard version of this method inadequately reproduces the stru ctural parameters of low-symmetry (C-1, C-S) paramagnetic species. A q uantum-chemical analysis of the radiospectroscopic information and of the stereoelectronic control of thermal transformations of conformers of RC 1 and 2 into their structurally nonequivalent distonic forms 3 a nd 4, respectively, was carried out.