Kinetics of molecular motions in liquids and its correlation with kinetics of radical liquid–phase reactions

Stable nitroxide radicals and ESR techniques have been used to investigate rotational and translational motions of molecules in the liquid state. It is found that for hydrocarbons and molecules with low polarity the rotational frequencies are about an order of magnitude faster than translational encounters. Arrhenius parameters are reported for the rates of both types of processes. A scheme is given for the relation of these motions to radical recombination in solution and also to reactions requiring activation energy. The consequences of this scheme are examined. Such important properties as hydrodynamic fluidity, thermal conductivity, processes of extraction and solution, occurring in the liquid phase as well as at the interface are determined by mobility of particles in the liquid. The problem of molecular mobility is of essential significance for the kinetics of chemical and chemico-physical processes in the liquid phase. Application of both ESR techniques and stable nitroxide radicals for kinetic studies of molecular motions in liquids and the correlation between molecular mobility and the kinetic parameters of liquid-phase radical reactions have been studied in the present paper.     

Chemical polarization of nuclei in reaction of 2,6-di-tert-butylbenzoquinone diazide with primary amines

Conclusions A mechanism for the reaction of quinone diazides with primary amines was proposed on the basis of the chemical polarization of the nuclei.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2620–2622, November, 1972.     

Electronic interaction anisotropy between open-shell lanthanide atoms and helium from cold collision experiment

Based on measurements of the Zeeman relaxation in a cold gas of (3)He [C. I. Hancox, S. C. Doret, M. I. Hummon, L. Luo, and J. M. Doyle, Nature (London) 431, 281 (2004)], we show that the electronic interaction anisotropy between rare-earth atoms with nonzero electronic orbital angular momenta and helium is extremely small. The interaction of the rare-earth atoms with He gives rise to several adiabatic potentials with different electronic symmetries. It is demonstrated that the energy splitting between these potentials does not exceed 0.09 cm(-1) at interatomic distances larger than the turning point for collisions at 0.8 K, including the region of the van der Waals interaction minima.     

Dynamics and mechanism of the non-adiabatic transitions from the ungerade I2(D0+u) state induced by collisions with rare gas atoms

The stepwise three-photon two-color laser excitation scheme is used for selective population of the first-tier ion-pair D0(+)(u) state of molecular iodine. Collection and analysis of the luminescence after the excitation of the v(D) = 6, 8, 13 and 18 vibronic levels of the D state in the pure iodine vapor and the gas-phase mixtures with He, Ar and Xe provide the total and, whenever possible, partial rate constants for the collision-induced non-adiabatic transitions to the other ion-pair states of the first tier. Comparison with the analogous data obtained previously for the non-adiabatic transitions from the E0(+)(g) state reveals the similarity between two cases. For He, the D ? E transitions are preferable, whereas for Ar and Xe transitions to the D' and β states dominate at v(D) = 6, 8 and 13, in accord with the statistical considerations. Efficient population of the δ state at v(D) = 18 in Ar and Xe is the most prominent non-statistical feature observed. The vibrational product state distributions for the D → E transitions are also obtained. In contrast to the previously studied E → D transition, they show significant positive vibronic energy transfer. The measurements for He and Ar are accompanied by the quantum scattering calculations that reproduce well the main qualitative features of the experimental results.     

Electron release by a tertiary carbon atom

Summary Heterocyclic iminoxyl free radicals display the effect of electron release through a tertiary carbon atom via the sigma bond system of a molecule.     

A model of macroradical recombination in dilute solutions

The dependence of exchange rate constants and diffusion coefficients of stable macroradicals (modified polydimethylsiloxane ($\text{P}\text{= 15, 29, 97}$) and polyethylenoxide ($\text{P}\text{= 25, 47, 140}$) on the length of polymer chain in various solvents is investigated. The results are compared with the rate constants for diffusive bimolecular recombination of macroradicals of various lengths. The dependence of rate constants of exchange and combination for macroradicals of different lengths obey the same law.The rate of combination for macroradical with P = 15-10⁵ is shown to depend mainly on the mobility of an active centre, limited by diffusion of the whole macromolecule. The diffusion rate constant of combination can be described by the Smoluchowski equation in which the radius of an active centre is used as the effective radius of interaction.A model of bimolecular termination of macroradicals, a model of “freely penetrating coils” (FPC), is proposed. It implies that k_ter ～ P^{?0.9 ± 0.1} (for “good” solvents). The reactivity of an active centre in recombination is independent of the length of a macroradical chain for P > 15.The exchange interaction in a radical pair broadens the ESR lines of radicals and recombination with equal effectiveness.