Specific chemical behavior of NdII and DyII iodides in reactions with aromatic compounds

Benzene, toluene, tert-butylbenzene, or biphenyl virtually do not react with NdI₂ (1) or DyI₂ (2) in THF at –20 °C but appreciably accelerate the reactions of these salts with solvents, resulting in LnI₃ and intractable mixtures of products of the general composition [LnI(H)(R)(THF)] (R are fragments of the THF molecule). The same effect is induced by the addition of diphenylmercury or tetraphenyltin to solutions of 1 or 2. Phenol easily oxidizes 1 and 2 to give at 0 °C the PhOLnI₂(THF) _x complexes (x = 3, 4) in 55—95% yields. At –90 °C, iodide 2 is converted into a similar complex PhODyI₂(THF)₄, whereas 1 gives a mixture of PhONdI₂(THF)₄, (PhO)₂NdI(THF)₅, NdI₃(THF)₃, and [NdI(H)R(THF)]. A plausible pathway of the reactions including the intermediate formation of extremely reactive monovalent lanthanide iodides LnI is discussed.     

Peripheral chemical reactions

Forward scattering of the products of direct exoergic atom transfer reactions is proposed as an indication for a peripheral attraction: a reaction in which an atom at the periphery of the reactants is abstracted. Model computations for the O(¹D) + N₂O reaction are used to illustrate the proposed mechanism. The opacity function has a peak at higher impact parameters which is correlated with the forward scattering. Potential energy surfaces which do not manifest peripheral attraction lead to backwards scattering of the products.     

Valency changes in chemical reactions

An analysis of valence changes in selected organic gas phase reactions, calculated on SINDO1 potential surfaces, is performed. It is shown that transition states and intermediates have diradical character if singlet and triplets states are nearly degenerate. As a consequence, normal valencies are expected in Woodward-Hoffman allowed reactions and reduced valencies in forbidden reactions. The formalism is also applied to cationic reactions, but the effects of valency changes are less pronounced.     

Independence of chemical reactions

Up to this time the existence of physically true dependences between elementary reactions has been a returning question. The goal of this paper is to show that the real elementary reactions of a mechanism are practically independent. Introducing the concept of the space-time volume of a reaction (the reciprocal of the reaction rate) it is shown that, except for extremely fast processes (explosions), the reactions form very dilute systems. This systems must be ideal in the sense that interactions between elementary processes are very rare. The system exhibits some analogies with a dilute gas or solution. The extents of interactions can be calculated and the limits of independence estimated in this way.

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化学反应的内禀反应坐标法VI. 甲胺脱氢反应的反应路径解析

本文用内禀反应坐标(IRC)法对甲胺的1,1-和1,2-脱氢反应途径进行了微观动力学解析。在RHF/4-31G水平上确定了反应的过渡态结构和势能变化曲线,得到了活化能、反应热、频率因子和活化熵等物理量。模式选择研究表明:1,1-和1,2-脱氢反应过程的反应坐标(IRC)分别与反应物中频率为1057和1348cm^-^1的两个变形振动模式相联结。在每条反应途径上都存在正则坐标间的振动耦合。本文的计算为激光诱导和模式选择化学反应的研究提供了重要信息和理论指导。     

Calculating chemical electron-polarization in triplet-molecule reactions

It is assumed that orientation fluctuations for molecules in a liquid form an uncorrelated Markov process, and an expression is derived in quadratures for the initial chemical polarization of the electrons formed by the triplet mechanism. The expression applies for any magnetic field strength and solvent viscosity. If the molecular rotations are slow and the magnetic field is weak, one can perform numerical calculations on the electron chemical polarization.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 203–206, March–April, 1986.     

Laser control of chemical reactions

Chemical reactions are at the heart of chemistry and the dream of controlling the outcome of these reactions is an old one. Thus, with given reactants, a solvent and perhaps assisted by a catalyst, we would like to 'steer' the reactants into a particular desired product. This review focuses on how to control the dynamics of chemical reactions, beyond traditional temperature control, with the emphasis on unimolecular reactions. The electromagnetic radiation of lasers can induce so-called coherent dynamics. The recent theoretical and experimental results on this coherent control are explained and illustrated with computational and experimental examples.     

Geometric description of chemical reactions

We use the formalism of Geometrothermodynamics to describe chemical reactions in the context of equilibrium thermodynamics. Any chemical reaction in a closed system is shown to be described by a geodesic in a 2-dimensional manifold that can be interpreted as the equilibrium space of the reaction. We first show this in the particular cases of a reaction with only two species corresponding to either two ideal gases or two van der Waals gases. We then consider the case of a reaction with an arbitrary number of species. The initial equilibrium state of the geodesic is determined by the initial conditions of the reaction. The final equilibrium state, which follows from a thermodynamic analysis of the reaction, is shown to correspond to a coordinate singularity of the thermodynamic metric which describes the equilibrium manifold.     

Radiofrequency labelling of molecules in chemical reactions

A method of radiofrequency labelling of molecules in chemical reactions has been proposed. It is based on selective RF pumping of molecules and on tracing the transformation of this label in the reaction products by the NMR spectra. Applications of this method in studying one-way reaction mechanisms are illustrated by some experimental examples.     

Bifurcations of dividing surfaces in chemical reactions

We study the dynamical behavior of the unstable periodic orbit (NHIM) associated to the non-return transition state (TS) of the H(2) + H collinear exchange reaction and their effects on the reaction probability. By means of the normal form of the Hamiltonian in the vicinity of the phase space saddle point, we obtain explicit expressions of the dynamical structures that rule the reaction. Taking advantage of the straightforward identification of the TS in normal form coordinates, we calculate the reaction probability as a function of the system energy in a more efficient way than the standard Monte Carlo method. The reaction probability values computed by both methods are not in agreement for high energies. We study by numerical continuation the bifurcations experienced by the NHIM as the energy increases. We find that the occurrence of new periodic orbits emanated from these bifurcations prevents the existence of a unique non-return TS, so that for high energies, the transition state theory cannot be longer applied to calculate the reaction probability.     

Infrared laser induced chemical reactions

It is shown that a high power infrared laser can enhance a chemical reaction (by lowering the activation energy) even if the reactants are infrared inactive.     

Dynamics of nonadiabatic chemical reactions

New methods are proposed to treat nonadiabatic chemical dynamics in realistic large molecular systems by using the Zhu-Nakamura (ZN) theory of curve-crossing problems. They include the incorporation of the ZN formulas into the Herman-Kluk type semiclassical wave packet propagation method and the trajectory surface hopping (TSH) method, formulation of the nonadiabatic transition state theory, and its application to the electron transfer problem. Because the nonadiabatic coupling is a vector in multidimensional space, the one-dimensional ZN theory works all right. Even the classically forbidden transitions can be correctly treated by the ZN formulas. In the case of electron transfer, a new formula that can improve the celebrated Marcus theory in the case of normal regime is obtained so that it can work nicely in the intermediate and strong electronic coupling regimes. All these formulations mentioned above are demonstrated to work well in comparison with the exact quantum mechanical numerical solutions and are expected to be applicable to large systems that cannot be treated quantum mechanically numerically exactly. To take into account another quantum mechanical effect, namely, the tunneling effect, an efficient method to detect caustics from which tunneling trajectories emanate is proposed. All the works reported here are the results of recent activities carried out in the author's research group. Finally, the whole set of ZN formulas is presented in Appendix.     

Macrokinetics of laser-induced chemical reactions in gases

This paper deals with the problem of laser radiation interaction with chemical gas. The review of numerical simulation results on the basis of three different models is presented. The main modes of the system behavior and the conditions, with various processes (diffusion, thermoconductivity, thermal diffusion, heat effect of the reaction and others) contributing to their realization, have been established. Theorems about the convergence of finite difference schemes have been proved.