Kinetics of nucleophilic substitution

What product would you expect from a nucleophilic substitution reaction of ( M-bromo-l-phenylethane with cyanide ion, C=N Show the stereochemistry of both reactant and product, assuming that inversion of configuration occurs. 

Strategy Identify the outgoing group (Br ) and replace it with the incoming nucleophile ( CN), while changing the stereochemistry at the reacting center. 

Solution Draw the R enantiomer of the reactant, and then change the configuration of the chirality center while replacing the —Br with a -CN. 

Chemists often speak of a reaction as being fast or slow. The exact rate at which a reactant is converted into product is called the reaction rate and can often be measured. The determination of reaction rates and of how those rates depend on reactant concentrations is a powerful tool for probing reaction mechanisms. Let s see what can be learned about the nucleophilic substitution reaction from a study of reaction rates. 

---

Kinetics of Nucleophilic Substitution Reactions of Polyfluoroaromatic Compounds Rodionov, P P, Furin, G G J Fluorine Chem 47. 361 34 105 ... 

Kinetics of Nucleophilic Substitution Reactions of Polyfluoro Aromatic Compounds (Russ) Rodionov, PP, Funn, G G hv Sib Old Akad NaukSSSR 3-26 87 B- [Pg.21]

German ED, Dogonadze RR. 1974. The kinetics of nucleophilic substitution processes in the alkyl halides. Part A—theory. Int J Chem Kin 6 457-466, and references therein. 

Kinetics of Nucleophilic Substitution Reactions of Polyfluoro Aromatic Compounds ... 

The kinetics of nucleophilic substitution reactions have been studied in greater detail than any other type of reaction because they don t always proceed through the same mechanism. Consider the reaction between the OH ion and t-butyl bromide, for example. 

The kinetics of nucleophilic substitution at the silicon atom assisted by uncharged nucleophiles have been studied by Corriu et at. (248-251). Hydrolysis of triorganochlorosilanes induced with HMPA, DMSO, and DMF was used as the model. The reaction proceeded according to the third-order kinetic law, first order with respect to the nucleophile, the silane, and the silylation substrate. Very low values of activation enthalpy and high negative entropy of activation were observed (Table VI). These results were taken as evidence for the intermediacy of silicon hypervalent species (249,251) however, they are also perfectly consistent with... 

In this chapter we report on an investigation of the kinetics of this reaction with several monomers. Bunnett and Levitt have studied the kinetics of nucleophilic substitution between p-substituted bromobenzenes and sodium methoxide (1) and found these reactions to be second order. Therefore, for a polymer-forming reaction between difunctional reactants, one would expect a second-order reaction with respect to the concentra-... 

So far, we have focused our discussion on the relative nucleophilicities of natural nucleophiles. Let us now consider how certain structural features of the organic molecule (i.e., type of leaving group, type of carbon skeleton) determine the kinetics of nucleophilic substitution. In Table 3, the (neutral) hydrolysis half-lives are given for various monohalogenated compounds at 25°C. Also indicated are the postulated reaction mechanisms with which these compounds undergo SN reactions. As can be seen from Table 3, the carbon-bromide and carbon-iodine bonds hydrolyze fastest, about one to two orders of magnitude... 

To account for these unusual results and the role of the free-radical character, a mechanism that implies that NH—CO—PTM- is a good leaving group in 8, 2 reactions has been proposed. It is based on the quantum-mechanical approach used to account for the kinetics of nucleophilic substitution in benzyl halides, which involves a diradicaloid configuration in the relevant transition state. The latter would be particularly stabilized by the radical character of the labelled glycine. 

L. Ya. Zakharova, R. A. Shagidulhna, F. G. Valeeva, E. P. Zhil tsova, L. A. Kudryavtseva, Kinetics of nucleophilic substitution reactions in ordered media, Russ. J. Phys. Chem., 2000, 74, 1821-1824. 

The kinetics of nucleophilic substitution of the methoxy group in methoxy-butenone by the diethylamino group has been studied (91 Mil).Thus, the reactions of 4-heterobut-3-en-2-ones with amines presented below often involve the transamination step. 

Many questions can be raised at this stage. What are the kinetics of nucleophilic substitution, and how does this information help us determine the underlying mechanism What happens with optically active haloalkanes Can we predict relative rates of substitution These questions will be addressed in the remainder of this chapter. 

---