Orientation in Disubstituted Benzenes

A brief account of aromatic substitution may be usefully given here as it will assist the student in predicting the orientation of disubstituted benzene derivatives produced in the different substitution reactions. For the nitration of nitrobenzene the substance must be heated with a mixture of fuming nitric acid and concentrated sulphuric acid the product is largely ni-dinitrobenzene (about 90 per cent.), accompanied by a little o-dinitrobenzene (about 5 per cent.) which is eliminated in the recrystallisation process. On the other hand phenol can be easily nitrated with dilute nitric acid to yield a mixture of ortho and para nitrophenols. It may be said, therefore, that orientation is meta with the... 

Some data relating to orientation of disubstituted benzenes are shown in Table 26. Thus the halogenation and tritylation ° of aniline derivatives results in substitution chiefly as expected fi om the -f-iZ effect. References on nitration and sulphonation have not been included in Table 26, since these processes often lead to oxidation products, making the orientational comparison in these compounds doubtful. 

The orientation of disubstitution in naphthalene follows a similar pattern to that encountered in benzene ... 

Optical activity, retention in the Stevens rearrangement 418 Optical-rotatory dispersion, in configuration assignment 136 of amino acids 134, 135 Orientational control, in exchange reactions 260 in halogenation 257, 263 in tritylation 263 of disubstituted benzenes 263 Orientational effect 250, 251 Orton rearrangement 637 Oxamidinium salts 734—737 from tetraaminoethylencs 721, 722 hydrolysis of 731... 

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