Functional group electronegative atoms

Electronegativity is a fundamental characteristic of atoms that is transferred into functional groups. Electronegativity correlates strongly with position in the periodic table. 

Effective electron donors include atoms or functional groups with lone pairs on their attachment points and functional groups containing atoms with low electronegativities. 

Most organic compounds are electrically neutral they have no net charge, either positive or negative. We saw in Section 2.1, however, that certain bonds within a molecule, particularly the bonds in functional groups, are polar. Bond polarity is a consequence of an unsymmetrical electron distribution in a bond and is due to the difference in electronegativity of the bonded atoms. 

This bistability is favoured by structures, which will adopt n—stacked motifs, i.e. lamellar molecules. In addition the tendency to adopt the planar structure is enforced by the presence of electronegative heteroatoms (currently restricted to N), which lead to a propensity of in-plane electrostatic S- N contacts between rings. These may comprise heterocyclic S- N contacts or S- N contacts to other functional groups such as the pyrazine or cyano nitrogen atoms. 

FIGURE 1. The relationships between the methyl deviation, 5(CH3— Z), and Pauling electronegativity of the bonded Z atom in various homologous functional group series, CH3—(CH2)m—Z. See References 17b and 18... 

Table 5 includes compounds with electronegative atoms singly bonded to Sn, such as halo, hydroxy, alkoxy, acyloxy, amino and their analogues. Acyloxy and analogous groups may appear as bidentate functions due to additional coordinative bonds established with a second oxygen atom, but this takes place with expansion of the coordination number of the tin atom to values higher than 4. 

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