Neighbouring groups, definition

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). 

For a rigorous definition of neighbouring groups see IUPAC, Commission on Physical Organic Chemistry. P Muller, ed. Glossary of terms used in physical organic chemistry. Pure App Chem 66 45, 1994. 

In solid state chemistry where there are often a number of equal short interatomic contacts, the simplest definition of coordination number is the number of nearest neighbours. In coordination chemistry (solid, solntion and gas phases) a more practical definition of coordination number is the number of atoms or ligating groups (such as a C=C double bond) bound to a metal. Thus in [CoCl4] the coordination nnmber is four. The majority of coordination complexes are either 4- or 6-coordinate. For... 

The size of an atom is not a simple concept. An inspection of the wave function for any atom shows that it is asymptotic to infinity (i.e. / becomes properly zero only at an infinite distance from the nucleus), so some practical definition of size is required. The previously discussed atomic properties are those of isolated gaseous atoms, but when sizes are discussed it is essential to consider the physical form of an element, whether it is monatomic like the Group 18 gases, whether it is metallic (in which case each atom is surrounded by between 12 and 14 nearest neighbours) or whether it is molecular and participating in covalent bonding. 

---