Directing effects, of substituents

Often the directing effects of substituents reinforce each other Brommation of p mtrotoluene for example takes place at the position that is ortho to the ortho para directing methyl group and meta to the meta directing nitro group... 

Because nitration has been studied for a wide variety of aromatic compounds, it is a useful reaction with which to illustrate the directing effect of substituent groups. Table 10.3 presents some of the data. A variety of reaction conditions are represented, so direct comparison is not always valid, but the trends are nevertheless clear. It is important to remember that other electrophiles, while following the same qualitative trends, show large quantitative differences in position selectivity. 

Table 11.1 Directive Effect of Substituents on Inward/Outward Conrotation in Cyclobutene Ring Opening"...

This difference in selectivity makes it necessary to consider both the substituent and the reagent when discussing the directing effects of substituents to a much larger extent than is necessary in the benzene series. 

Inductive and resonance effects account for the directing effects of substituents as well as for their activating or deactivating effects. Take alkyl groups, for instance, which have an electron-donating inductive effect and are ortho and para directors. The results of toluene nitration are shown in Figure 16.13. 

A Summary of Substituent Effects in Aromatic Substitution A summary of the activating and directing effects of substituents in electrophilic aromatic substitution is shown in Table 16.2. 

However, the hydride reduction of FeCp(arene)+ salts [124, 125] gives [FeCp(r 5-cyclohexadienyl)] complexes [125, 126] (via an ET mechanism [127] for the directing effect of substituents see Refs. [126, 128-130]. The electrochemical reduction of the carboxylic substituents at an Hg cathode in water leads to the primary alcohol [131-133] Eq. (39) ... 

Sulfinyl and sulfonyl groups were involved in early studies of the directive effects of substituents in nitration and other reactions with electrophilic reagents. Thus Twist and Smiles (in 1925) showed that nitration of phenyl methyl sulfone gave exclusively 3-nitrophenyl methyl sulfone. The results of bromination and sulfonation were analogous, so S02Me was established, like NO2, as a mefa-directing group. 

The structural theory of organic chemistry was developed in the last half of the nineteenth century. It led to the concept that chemical, physical and biological properties of all kinds must be a function of structural change. The earliest structure-property relationships (SPR) were qualitative. Examples are the directional effect of substituents on the benzene ring with respect to electrophilic aromatic substitution and orientation in... 

Considering the directing effect of substituents (71AHQ13J235, 63AHC(l)l), the mass of detail from the literature was first systematized by Gronowitz (63AHC[Pg.752]

Interesting recent work by Addy and co-Workers1917 sheds additional light on the directive effect of substituents for the reaction of benzylamine with various styrene oxides. The pronounood tendency of a p-methyi substituent to foster abnormal attack, as shown in JEq. <626), is especially noteworthy. 

Because the position of electrophilic attack on an aromatic ring is controlled by the directing effects of substituents already present, the preparation of disubstituted aromatic compounds requires that careful thought be given to the order of introduction of the two groups. 

Gronowitz first applied the modern electronic theories of organic chemistry to elucidating the directing effects of substituents in the thiophene ring259 and has summarized concepts and experimental data in a recent review.2 The same rules can be extended without appreciable modifications to the other monocyclic systems fur an, selenophene, and pyrrole. 

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