Neighbouring-group systems

Exhaustive studies on well-defined systems are rather scarce (4) nevertheless 3 systems thoroughly analyzed by independant research groups are of outstanding interest a) the quaternization of polyvinylpyridines by alkyl halogenides (20-25) b) the chlorination of polyethylene (13,26-28) c) the basic or acid hydrolysis of PMMA (29-31). On the other hand, neighbouring groups effects have been quantitatively taken into account for the kinetic analysis of periodate oxidation of amylose (32,33). 

To conclude, kinetic measurements and structural analysis of the copolymers have allowed a quantitative and self-consistent description of the reaction of RCI Li species on PMMA taking into account PMMA chain reactivity through the simplified model of the nearest neighbouring group effects. Two main features are particularly relevant the definite influence of tacticity, and the independance of the reaction process on the total charge of the copolymer. In this sense, the R-C Li/PMMA systems are closed to the PMMA basic hydrolysis in presence of excess base. (29,31). 

Systematic investigation of the stereo- and regio-control of electrophilic additions to cyclohexene systems (steroids in particular) by neighbouring groups allowed formulating certain principles, which govern the reactivities toward representative electrophiles,... 

The initial suggestion that a remote double bond could be involved in a displacement reaction was made by Shoppee in 1946 in order to account for the stereochemical results of the transformations of 3-cholesteryl derivatives Building on the considerable work then underway on neighbouring group participation in ionization reactions Shoppee suggested that the double bond in the cholesteryl system, 1, could function in a similar manner to Lewis base containing groups such as acetate or alkoxy, etc. 

---