Stereochemistry in Substitution Reactions

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- 

Sample Phase6 Inversion (%) Sample Phase Inversion (%) 

An interesting behavior of the retention/inversion ratio in dl- and meso-(CH3CHCl)2 was observed upon dilution with several compounds (Fig. 1) (91). This effect was assigned to the relative concentrations of 

No inversion of configuration was found in the case of 18F-for-F substitution in gaseous dl- and meso-(CHFCl)2, in accord with the results obtained with the same compounds for recoil T and 38C1 atoms (96). 

After the formation of the carbocation, two competing processes occur in the moderated systems racemization and Cl+ transfer. In the case of the meso compound, front attack leads to the thermodynamically stable erythro form, whereas in the dl system, the less stable threo diaste-reomer is formed, which readily leads to racemization. 

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