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。     

A chromatographic method for detection of end points in chemical reactions

Summary Gas chromatography is recognized as an analytical technique possessing desirable advantages for a wide range of applications. The purpose of this work is to demonstrate the usefulness of GC instrumentation for determining values of end-points for a variety of reactions. Gas chromatographic titrimetry may be characterized as that in which the change of peak-height ratio of the reaction during a titration is recorded as a function of titrant added. The experimental data are fitted to simple first-order interpolation equations, so that the titration curve, when extrapolated, intersects the volume axis, the point of intersection being the equivalence-point volume. The end-point values are in good agreement with those reported in the literature and with control measurements. From the results it is concluded that the method can be used with high confidence to determine end-point values in a fast and easy way.     

Consecutive reactions in chemical kinetics: A method for the treatment of experimental data

A method is proposed for the treatment of data from a kinetic system of first order consecutive reactions by using an optimization procedure which converges to the correct solution of the two mathematically possible solutions and which does not need initial estimates of the parameters close to those to be determined.

---

, , , .

     

A novel method for calculating rate constants of diffusion-influenced reactions

In the present work we suggest a method for calculating rate constants of chemical processes affected by mobility of reactants. The method is based on the encounter theory. Unlike the widely accepted model of collision complexes it provides a general formal solution for practically arbitrary reaction scheme.     

A general method for the computation of probabilities in systems of first order chemical reactions

We present a general method for the computation of molecular population distributions in a system of first-order chemical reactions. The method is based on the observation that the molecules in first-order reactions do not interact with each other. Therefore, the population distributions are a convolution of densities for one molecule. With this method one can study reactions involving any number of molecules. Such analysis is demonstrated on several examples, including an enzyme catalyst reaction and a first-order reaction chain.     

A novel one-step chemical method for preparation of copper nanofluids

This paper presents a novel one-step method for preparing of copper nanofluids by reducing CuSO(4).5H(2)O with NaH(2)PO(2).H(2)O in ethylene glycol under microwave irradiation. Nonagglomerated and stably suspended Cu nanofluids are obtained. The influences of CuSO(4) concentration, addition of NaH(2)PO(2), and microwave irradiation on the reaction rate and the properties of Cu nanofluids were investigated by transmission electron microscopy, infrared analysis, and sedimentation measurements. It is found to be a fast, efficient one-step chemical method to prepare Cu nanofluids.     

Improved version of Doyle integral method for nonisothermal kinetics of solid-state reactions

An improved version of Doyle integral method for the determination of the kinetic parameters from nonisothermal thermoanalytical data has been presented. The relative errors involved in the activation energy and frequency factor determined from Doyle integral method and its improved integral method have been estimated. The results have shown that the precision of the improved version of Doyle integral method for the determination the kinetic parameters (including the activation energy and frequency factor) is much higher than that of Doyle integral method.     

NDDO quantum chemical calculations of molecules. A comparison between the modified version and the AM1 method

Advantages and disadvantages of two approaches to electronic structure calculations of molecules using the NDDO approximation are revealed.     

1,2-Ditellurolane: A new synthetic method, structure and chemical reactions

A simple method for the synthesis of 1,2-ditellurolane is proposed, based on the reaction of elemental tellurium with 1,3-dihalopropane in a system of hydrazine hydrate and alkali followed by the effect of organic solvent on the first formed poly(trimethyleneditellurides). The products of the oxidation and reduction of 1,2-ditellurolane were characterized and its spectral characteristics were analyzed. Dedicated To Academician Of The Russian Academy Of Science Mikhail Grigor’evich Voronkov on his 85^th Birthday. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, 1705–1713, November 2006.     

A graph theory method for determining the basis of homodesmic reactions for acyclic chemical compounds

One of the techniques for theoretically determining enthalpies of formation of organic compounds is the method of homodesmic reactions. In this work, a graph theory interpretation of acyclic chemical compounds was presented, and an algorithm for constructing a basis of homodesmic reactions was developed, which makes it possible to use a homodesmic approach to calculating the enthalpy of formation. Using the developed algorithm was exemplified by building the basis of homodesmic reactions for the butyramide molecule.     

A study of chemical reactions in coarse-grained simulations

We introduce a reaction model for use in coarse-grained simulations to study the chemical reactions in polymer systems at mesoscopic level. In this model, we employ an idea of reaction probability in control of the whole process of chemical reactions. This model has been successfully applied to the studies of surface initiated polymerization process and the network structure formation of typical epoxy resin systems. It can be further modified to study different kinds of chemical reactions at mesoscopic scale.     

A polynomial version of the generator coordinate Dirac-Fock method

A polynomial version of the Generator Coordinate Dirac-Fock (p-GCDF) method is introduced and applied to develop Adapted Gaussian Basis Sets (AGBS) for helium- and beryllium-like atomic species (He, Ne +8, Ar +16, Sn +48, Be, Ne +6, Ar +14, and Sn +46) and for Kr and Xe atoms. The Dirac-Fock-Coulomb and Dirac-Fock-Breit energies obtained with these basis sets are in excellent agreement with numerical finite-difference calculations. Moreover, the sizes of the AGBS generated here with the p-GCDF method are significantly smaller than the size of previous relativistic Gaussian basis sets.     

K-leap method for accelerating stochastic simulation of coupled chemical reactions

Leap methods are very promising for accelerating stochastic simulation of a well stirred chemically reacting system, while providing acceptable simulation accuracy. In Gillespie's tau-leap method [D. Gillespie, J. Phys. Chem. 115, 1716 (2001)], the number of firings of each reaction channel during a leap is a Poisson random variable, whose sample values are unbounded. This may cause large changes in the populations of certain molecular species during a leap, thereby violating the leap condition. In this paper, we develop an alternative leap method called the K-leap method, in which we constrain the total number of reactions occurring during a leap to be a number K calculated from the leap condition. As the number of firings of each reaction channel during a leap is upper bounded by a properly chosen number, our K-leap method can better satisfy the leap condition, thereby improving simulation accuracy. Since the exact stochastic simulation algorithm (SSA) is a special case of our K-leap method when K=1, our K-leap method can naturally change from the exact SSA to an approximate leap method during simulation, whenever the leap condition allows to do so.     

A density functional study of chemical reactions

Density functional theory (DFT ) was used to study reactions involving small molecules. Relative energies of isomers and transition structures of diazene, formaldehyde, and methylenimine were determined using various DFT functionals and results were compared with MP 2 and MP 4 calculations. DFT reaction barriers were found to be consistently lower. For some reactions, such as OH + H₂→ H₂O + H, gradient-corrected functionals predict very low or nonexistent barriers. The hybrid Hartree–Fock–DFT adiabatic connection method (ACM ) often provides much better results in such cases. The performance of several density functionals, including ACM , was tested in calculations on over 100 atomization, hydrogenation, bond dissociation, and isodesmic reactions. The ACM functional provides consistently better geometries and reaction energetics than does any other functional studied. In cases where both HF and gradient-corrected DFT methods underestimate bond distances, the ACM geometries may be inferior to those predicted by gradient-corrected DFT methods. © 1995 John Wiley & Sons, Inc.     

In situ version of radical-chain substitution reactions

Peroxy acetals derived from an ether and a hydroperoxide can be prepared in situ and used without isolation to effect sulfochlorination of n-alkanes or chlorination of toluene to benzyl chloride.     

A pulse polarograph for the measurement of fast chemical reactions

A fast pulse polarograph suitable for the measurement of fast homogeneous reactions and of electrode reactions is described in detail. The fast charging of the double layer (<10^?5s) is realized either by charge injection or by iR-compensation. The minimum delay time between the charging of the double layer and the measuring of the current is about 7 μs. The applicability of the instrument is demonstrated with the measurement of the dissociation rate of Cd(CN)₄^2?.