Aromatic Compounds Containing Two or More Unlike Groups

AROMATIC COMPOUNDS CONTAINING TWO OR MORE UNLIKE GROUPS 

Nitrobromobenzenes, Br.C6H4.NO2.—Three compounds of this formula exist. When bromobenzene is nitrated, the bromine atom sends the nitro group to the para and ortho positions, the chief product of the reaction being p-nitrobromobenzene (m.p. 126°). On the other hand, when nitrobenzene is bromi-nated, the negative nitro group sends the halogen atom to the meta position, and an excellent yield of m-nitrobromobenzene (m.p. 56°) is formed. 

The chemical properties of the three isomers illustrate the effect of the relative position of substituents on their activity. o-Nitrobromobenzene (m.p. 43°) is converted into o-nitroaniline when heated at 190° with an alcoholic solution of ammonia, and into o-bromophenol when heated at a high temperature with water and potassium hydroxide. In one reaction the halogen atom is removed by ammonia, and in the other the nitro group by potassium hydroxide. p-Nitrobromobenzene enters into similar reactions, but the meta compound is not affected by the 

The compounds formed by nitrating the isomeric nitro-bromobenzenes furnish an illustration of the principle in regard to the orienting effect of substituents on entering groups. The structures of the products formed are shown by the following formulas — 

Benzoin, CeHB.CO.CHOH.CeHs, is an example of a ketone-alcohol. The method by which it is prepared from benzoic aldehyde has been given in section 566. The oxygen 

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