Antisteric choice

I = 0.44).When the same reagents are reacted 1n (1 0,5) amounts tne choice is opposite (1=4 antisteric process). 

It was foimd however, that in some other cases the choice corresponds to opposite configuration, that is to an antisteric type process. 

We have demonstrated in the case o few thiiranes, oxiranes and recently for a,a disubstituted 3 propiolactones (36) that the type of the choice (homosteric or antisteric) is depending only on the x/y ratio i.e. the ratio of alkylalkoxide species over dialkoxide species. 

The stereoelective choice of monomers is however in agreement with configuration rules as seen from the sign of optical activity of unreacted monomer. Homosteric and antisteric processes are observed with considerable amount of a-scission (39). According to the chemical composition of these initiators a cationic character of the latter seems to be excluded and therefore this particular behaviour could be due to some steric reasons which are not yet completely understood. New studies are now in progress. 

---