Stereochemistry of substitution reactions

While it may be convenient to use optically active reactants to probe the stereochemistry of substitution reactions, it should be emphasized that the stereochemistry of a reaction is a feature of the mechanism, not the means of determining it. Thus, it is proper to speak of a substitution process such as the hydrolysis of methyl iodide as proceeding... 

TABLE 9. Stereochemistry of substitution reactions on methylcyclohexyl bromides by VLnSiiLi and MesGeLi... 

The specific feature of the bonds also affects its chemical behaviour and the stereochemistry of substitution reactions. For example in the conversion of (-) trans -2, 3 diphenyl cyclopropane carboxylic acid into (+) 1, 3 diphenylallene the optical activity is retained. 

The foregoing considerations show that, in order to reproduce the stereochemical trends, it is not necessary to introduce either d orbitals for the silicon atom or pseudo-rotations for the transition state. Conversely, the stereochemistry of substitution reactions on silicon compounds cannot be taken as a proof of d orbitals intervention in silicon chemistry. 

Chapter 8 discussed the stereochemistry of substitution reactions—that is, what happened to the stereochemistry when the reaction occurred at a carbon chirality center. This section discusses the regiochemistry of the elimination reaction—that is, what happens when a reaction can produce two or more structural isomers. The structural isomers that can often be produced in elimination reactions have the double bond in different positions. As shown in Figure 9.5, elimination of hydrogen chloride from neomenthyl chloride produces two structural isomers but in unequal amounts. 

Another important argument is provided by the stereochemistry of substitution reactions at silicon. In the optically active complex 6 nucleophilic substitution by H, OH-, or OMe- occurs with inversion of configuration at silicon, while retention was observed with the related... 

An important aspect of hot-atom chemistry concerns the stereochemistry of substitution reactions, particularly if the reactions proceed via retention or (Walden) inversion. Cross sections for the reac-... 

Stereochemical Considerations. Much attention has been directed toward the stereochemistry of substitution reactions of alkyl complexes. Substitution of MeMn(CO)s leads to cw-MeC(0)Mn(C0)4L initially, although the cis complex isomerizes to the trans eventually ... 

Problem 14.1 (a) What product would be formed if the reaction of r/5-4-bromo-cyclohexanol with OH" proceeded with inversion (b) Without inversion (c) Is it always necessary to use optically active comppunds to study the stereochemistry of substitution reactions ... 

They deserve a chapter on their own for at least three reasons. Firstly, they have been heavily used to study the complicated stereochemistry of substitution reactions at the phosphorus atom. This can be explained by the restriction of rearrangements that occurs when a P atom is placed in a cycle, although it is often found that in cyclic compounds the stereochemical course of the substitution is different to that of their acyclic counterparts. 

There is a real need for more research designed to collect good quantitative data on the stereochemistry of substitution reactions. An excellent start has been made on the hydrolysis of [Co(en)2LCl]"+ complexes. Some of the data obtained are shown in Table II. Having first decided on the label SnI or Sn2 for the reaction, it is possible to interpret the stereochemical results on the basis of the active intermediates proposed in Table III. Thus the SnI reactions of m-[Co(en)2LCl(]+ proceed with retention... 

Mechanisms of racemization of metal complexes, Eq. (56), are an integral part of the stereochemistry of substitution reactions. 

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