Phenyl groups, substituted, electronic effects

From the data presented in Table XIX for 5-substituted 2-indolyl groups, it can be concluded that by their inductive effect they are electron-withdrawing substituents, and that by their mesomeric effect they are weak electronreleasing substituents comparable to m- and p-substituted phenyl groups with electron-releasing substituents. 

Formic acid, pK 3.75, serves as the reference carboxylic acid. Benzoic acid is weaker because the phenyl group is electron-donating by resonance, stabilizing the protonated form. Methyl substituents are known to be electron-donating by induction, strengthening the electron-donating effect, making the meta- and para-substituted acids weaker than benzoic acid. 

A mechanism has been proposed to rationalize the results shown in Figure 23. The relative proportion of the A -pyrazolines obtained by the reduction of pyrazolium salts depends on steric and electronic effects. When all the substituents are alkyl groups, the hydride ion attacks the less hindered carbon atom for example when = Bu only C-5 is attacked. The smaller deuterohydride ion is less sensitive to steric effects and consequently the reaction is less selective (73BSF288). Phenyl substituents, both on the nitrogen atom and on the carbon atoms, direct the hydride attack selectively to one carbon atom and the isolated A -pyrazoline has the C—C double bond conjugated with the phenyl (328 R or R = Ph). Open-chain compounds are always formed during the reduction of pyrazolium salts, becoming predominant in the reduction of amino substituted pyrazoliums. 

Feng et al. [3] have studied the structural effect of acetanilide on the AAM polymerization either in water-for-mamide [3], water-acetonitrile [4], and water-DMF [26] mixed solution using Ce(IV) ion-acetanilide and its substituted derivatives as the initiator. The results showed that an electron donating substituent on the phenyl group would enhance the Rp, while an electron withdrawing group would decrease it, as shown in Table 1 [26]. 

As previously mentioned above, the chiral recognition abilities of the phenyl-carbamates of polysaccharides are greatly influenced by the substituents on the phenyl groups. In order to evaluate the effect of the substituents on the interaction between CSPs and solutes, the retention times of acetone and the first-eluted isomer of l-(9-anthryl)-2,2,2-trifluoroethanol (39) on 3- and 4-substituted CSPs are plotted against the Hammett parameter a of the substituents (Figure 3.33).130 The retention times of acetone tend to increase as the electron-withdrawing power of the substituents increases, whereas those of the first-eluted isomer of 39 tend to decrease. These results indicate that... 

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