Potential energy surfaces methyl chloride

The reaction between ammonia and methyl halides has been studied by using ab initio quantum-chemical methods.90 An examination of the stationary points in the reaction potential surface leads to a possible new interpretation of the detailed mechanism of this reaction in different media, hr the gas phase, the product is predicted to be a strongly hydrogen-bonded complex of alkylammonium and halide ions, in contrast to the observed formation of the free ions from reaction hr a polar solvent. Another research group has also studied the reaction between ammonia and methyl chloride.91 A quantitative analysis was made of the changes induced on the potential-energy surface by solvation and static uniform electric fields, with the help of different indexes. The indexes reveal that external perturbations yield transition states which are both electronically and structurally advanced as compared to the transition state in the gas phase. 

Most of these theoretical investigations have been carried out using methyl compounds as the substrate. For example, the Sn2 reaction between OFT and methyl chloride has been investigated for non-linear and linear collisions using ab initio molecular dynamics calculations.105 The potential energy surface was calculated at the MP2/6-311-I— -G(2df,2pd) level of theory and the collision energy was set at 25 kcal mor1. The results for 495 trajectories indicated that the reactants pass from the initial encounter complex to the transition state in 0.02 ps and to the product encounter... 

The Sn2 reaction in solution. We saw above the application of microsolvation to Sn2 reactions ([14, 15]). Let us now look at the chloride ion-chloromethane Sn2 reaction in water, as studied by a continuum method. Figure 8.2 shows a calculated reaction profile (potential energy surface) from a continuum solvent study of the Sn2 attack of chloride ion on chloromethane (methyl chloride) in water. Calculations were by the author using B3LYP/6-31+G (plus or diffuse functions in the basis set are considered to be very important where anions are involved Section 5.3.3) with the continuum solvent method SM8 [22] as implemented in Spartan [31] some of the data for Fig. 8.2 are given in Table 8.1. Using as the reaction coordinate r the deviation from the transition state C-Cl... 

For the reaction between methyl-chloride and ammonia we have studied a portion, including the transition state, of the potential energy surface performing numerically the geometry optimization. The computed activation free energy, 20.5 kcal/mol, is in substantial accord with recent calculations on the same reaction by Traong et al. [20]... 

B3LYP/6-31 lG-l-l-(d,p) calculations on the reactions of (1-chlorovinyl)- and (1-chlorocyclopropyl)magnesium chlorides solvated with two molecules of dimethyl ether, with a chloride ion, methyl anion, vinyl anion, or an acetylide anion showed that the reactions with magnesium compounds have lower AG values than either chloroethene or chlorocyclopropane. This is attributed to the longer, more reactive, C-Cl bond in the magnesium compounds. The potential energy surfaces, AG values, and the transition state structures for the reactions are given. 

Many studies on the direct reaction of methyl chloride with silicon-copper contact mass and other metal promoters added to the silicon-copper contact mass have focused on the reaction mechanisms.7,8 The reaction rate and the selectivity for dimethyldichlorosilane in this direct synthesis are influenced by metal additives, known as promoters, in low concentration. Aluminum, antimony, arsenic, bismuth, mercury, phosphorus, phosphine compounds34 and their metal complexes,35,36 Zinc,37 39 tin38-40 etc. are known to have beneficial effects as promoters for dimethyldichlorosilane formation.7,8 Promoters are not themselves good catalysts for the direct reaction at temperatures < 350 °C,6,8 but require the presence of copper to be effective. When zinc metal or zinc compounds (0.03-0.75 wt%) were added to silicon-copper contact mass, the reaction rate was potentiated and the selectivity of dimethyldichlorosilane was enhanced further.34 These materials are described as structural promoters because they alter the surface enrichment of silicon, increase the electron density of the surface of the catalyst modify the crystal structure of the copper-silicon solid phase, and affect the absorption of methyl chloride on the catalyst surface and the activation energy for the formation of dimethyldichlorosilane.38,39 Cadmium is also a structural promoter for this reaction, but cadmium presents serious toxicity problems in industrial use on a large scale.41,42 Other metals such as arsenic, mercury, etc. are also restricted because of such toxicity problems. In the direct reaction of methyl chloride, tin in... 

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