The nitro group as substituent

Among various groups considered in organic chemistry as 'substituents' the nitro group occupies a particular position since its action is both strong and reasonably predictable. Its effects have been quantitatively evaluated in the form of various substituent constants sigma which may be interpreted in terms of inductive, mesomeric and other effects. In the case of the nitro group the inductive effect is dominant. Of particular interest is the long standing problem of conjugation (negligible or appreciable) of the nitro group with the benzene ring in nitrobenzene.