P- Bromonitrobenzene

The compound l-bromo-4-nitrobenzene (p-bromonitrobenzene) can be brominated. What do you expect to be the major product and why Draw appropriate Lewis structures to support your answer. 

Aromatic halides don t react unless an electron-withdrawing group is attached to the ring. For example, bromobenzene doesn t react. An example showing the reaction when an electron-withdrawing group is present is illustrated in Figure 13-10, the nucleophilic substitution attack on p-bromonitrobenzene. 

Write chemical equations showing how you could prepare m-bromonitrobenzene as the principal organic product, starting with benzene and using any necessary organic or inorganic reagents. How could you prepare p-bromonitrobenzene ... 

An interesting case is provided by the nitration of aryl halides where the effect of the halogen is to deactivate the aromatic nucleus (by the -I effect) but to direct the incoming nitronium ion to the ortho and para positions as a result of the mesomeric interaction of the halogen lone electron pair with the charge developed in the corresponding intermediates [e.g. (5), in the formation of p-bromonitrobenzene from bromobenzene, Expt 6.20],... 

Bromine is an ortho, para-directing group. If it is introduced first, nitration of the resulting bromobenzene yields a mixture of o-bromonitrobenzene and p-bromonitrobenzene. 

Coupling of p-Bromonitrobenzene with Trimethylsilylacetylene in the Presence of Catalytic Amounts of Pd(PPhand Cul... 

To fully understand how substituents direct further substitution is important in planning the synthesis of a di-substituted aromatic compound. For example, there are two choices which can be made in attempting the synthesis of p-bromonitrobenzene from benzene (Following fig.) we could brominates first, then nitrate, or nitrate first than brominates. A knowledge of how substituents affect electrophilic substitution allows us to choose the most suitable route. 

Plazek and L. Kuczyriski [31] investigated the reactivity towards ammonia of bromine atoms in o-, m- and p- bromonitrobenzene. The bromine atom in a position ortho to the nitro group is the most reactive, while the bromine atom in the meta position is the least so. However, in the presence of copper catalyst (CuS04.5H20) there is not much difference between the reactivity of meta- and para- bromine atoms. The bromine atom in the ortho position remains the most reactive in the presence of a catalyst. 

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