Rate constants of the reactions of OH radicals with cyclopropane and cyclobutane

The kinetics of the reactions of hydroxy radicals with cyclopropane and cyclobutane has been investigated in the temperature range of 298–492 K with laser flash photolysis/resonance fluorescence technique. The temperature dependence of the rate constants is given by k₁ = (1.17 ± 0.15) × 10^?16 T^3/2 exp[?(1037 ± 87) kcal mol^?1/RT] cm³ molecule^?1 s¹ and k₂ = (5.06 ± 0.57) × 10^?16 T^3/2 exp[?(228 ± 78) kcal mol^?1/RT] cm³ molecule^?1 s^?1 for the reactions OH + cyclopropane → products (1) and OH + cyclobutane → products (2), respectively. Kinetic data available for OH + cycloalkane reactions were analyzed in terms of structure-reactivity correlations involving kinetic and energetic parameters.     

Limiting transition from the model of collective motion of π-electrons in molecules to the semiempirical Pariser-Parr-Pople theory

In the context of a two-parameter scheme (correlation and localization) we examine the region of applicability of various-electron theories. The limiting transition from the model of collective motion (MCM) to Pariser-Parr-Pople (PPP) theory shows that PPP theory is inconsistent. The PPP model Hamiltonian derived in the approximation of strong localization of-electrons has been invalidly extended to the region of weak localization, thus losing an important branch of low-lying collective-electron excitations. Inclusion of this branch qualitatively alters the results of PPP theory. Furthermore, the conclusion of PPP theory that there are no singlet excitations of the benzene molecule below 4.7 eV conflicts with several experiments.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 37–42, September, 1977.     

Calculation of orbital magnetic moments of π-electron terms of cyclic molecules in a collective-motion model

The magnetic moments of levels of ring -electron chains along a cyclic core of a molecule are calculated for various values of the form factor of the periodic potential of the -core field. The cases of short-range (flexible chain) and long-range (rigid chain) strong interelectron repulsion are considered. The magnetic moments of the flexible-chain levels are practically independent of the form factor. The magnetic moments of the rigid-chain levels are less than the corresponding moments of the flexible chain, but at certain values of the form factor resonance occurs and the rigid-chain moments approach those of the flexible chain. An anomalously large Zeeman splitting of the upper electron levels of large aromatic molecules is predicted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 37–42, October, 1976.