Pyridines and related nitrogen heterocyclic azabenzenoid compounds

It is clear from these data that ring N is a major factor affecting reactivity and orientation of attack in these systems. Nevertheless, pentafluoropyridine reacts with various nucleophiles to give products arising from exclusive attack at the 4-position (Table 9.7), whereas 37/-tetrafluoropyridine gives a mixture of both 4- and 6-attack 

There are other cases [102, 107] where the subtle interplay of solvent and steric effects has a profound effect on orientation of substitution. 

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Pyridines and related nitrogen heterocyclic (azabenzenoid) compounds Polyfluoroaromatic nitrogen heterocyclic systems are all activated, relative to the corresponding benzenoid compounds, towards nucleophilic aromatic substitution. The magnitude of this activation is illustrated by the effects of a ring nitrogen, relative to C—F at the same position, for attack by ammonia [91] (Figure 9.32). 

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