Ring-substituted anilines monosubstituted

Evaluation of the only appropriate Fukui function is required for investigating an intramolecular reaction, as local softness is merely scaling of Fukui function (as shown in Equation 12.7), and does not alter the intramolecular reactivity trend. For this type, one needs to evaluate the proper Fukui functions (/+ or / ) for the different potential sites of the substrate. For example, the Fukui function values for the C and O atoms of H2CO, shown above, predicts that O atom should be the preferred site for an electrophilic attack, whereas C atom will be open to a nucleophilic attack. Atomic Fukui function for electrophilic attack (fc ) for the ring carbon atoms has been used to study the directing ability of substituents in electrophilic substitution reaction of monosubstituted benzene [23]. In some cases, it was shown that relative electrophilicity (f+/f ) or nucleophilicity (/ /f+) indices provide better intramolecular reactivity trend [23]. For example, basicity of substituted anilines could be explained successfully using relative nucleophilicity index ( / /f 1) [23]. Note however that these parameters are not able to differentiate the preferred site of protonation in benzene derivatives, determined from the absolute proton affinities [24],... 

Derivatives of Biphenyl. By coupling diazo compounds and N-nitrosoacetyl derivatives obtained from substituted anilines with benzene, a large variety of biphenyl derivatives can be prepared in which only one of the rings is substituted. In this manner, the isomeric monosubstituted biphenyls, RCel CeHs, have been prepared in which R = Br, Cl, CH3, OCH3, NO2, CN, etc. The meta derivatives, such as 3-brQmobiphenyl (I), 3-nitrobiphenyl (II), and 3-cyanobiphenyl (III), are of particular interest because they cannot be prepared readily from biphenyl. The usefulness of the methods for the preparation of compounds of definite... 

In this review, attention is focused primarily on the oxidation mechanisms under the given conditions, which is the essential topic of interest for organic chemists. Reaction pathways will be outlined if they seem to be well established. However, even small differences in medium properties used by different researchers can lead to serious variations as will be shown in some examples. Anodic oxidation of unsubstituted aniline is discussed in Section II and electrode reactions of /V-substifilled and C-substituted anilines in Sections III and IV, respectively. In the last case, the oxidation of reactants with monosubstituted ring is presented first (para-substituents separately from the effects of ortho- and mefa-substituents), and next the oxidation of di- and trisubstituted anilines. In each part the processes in dipolar aprotic solvents, in particular in acetonitrile (ACN) and /V. /V-dimethylformamide (DMF), are compared with those proceeding in aqueous solutions, chiefly in commonly used acidic media. 

Other derivatives of pyrrole that are of interest as coupling components are indole (12.39) and substituted indoles. Indole may be considered as a pyrrole with a benzo ring fused to it, or as a cyclized derivative of an 7V-monosubstituted aniline. For an aniline compound one expects either a C-coupling in the 5-position or an TV-cou-... 

Some substituents are so strongly activating that no catalyst is needed, and it is often difficult to stop substitution before more than one new substituent has been added to the ring. For example, many anilines are brominated with Bt2 alone to give 2,4,6-tribromoanilines (Fig. 14.88). Phenols are also highly activated toward further substitution to give polysubstituted products. Mild conditions are needed to restrict the reaction to monosubstitution. 

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