A nitrogen lone pair activates even more strongly

A nitrogen lone pair activates even more strongly 

The NMR of aniline supports the increased electron density in the n system—the shifts for the aromatic protons are even smaller than those for phenol showing greater electron density in the ortho and para positions. 

Just how good nitrogen is in donating electrons into the jc system is shown by comparing the relative rates for the bromination of benzene, methoxybenzene (anisole), and N /V-dimethylaniline. 

The high reactivity of aniline can actually be a problem. Suppose we wanted to put just one bromine atom on to the ring. With phenol, this is possible (p. 557)—if bromine is added slowly to a solution of phenol in carbon disulfide and the temperature is kept below 5 °C, the main product is para-bro-mophenol. Not so if aniline is used—the main product is the triply substituted product. 

The lone pair electrons on the nitrogen atom of the amide are conjugated with the carbonyl group as usual but they are also delocalized into the benzene ring, though more weakly than in the amine. Reaction still occurs in the ortho and para positions (mainly para) but it occurs once only. 

After the reaction, the amide can be hydrolysed (here, with aqueous acid) back to the amine. 

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A NITROGEN LONE PAIR ACTIVATES EVEN MORE STRONGLY... 

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