Effects 1-phenyl group substitution

The analysis of the effect that the different substituents may have on the rate coefficients in this case is particularly hard to perform by using simple inductive effects, as described for instance by the Hammett substituent constants. Note that, despite the fact that most of the 28 carbenium ions exhibit para substitution, the general structure on top of Chart 6, shows a complex substitution pattern at the carbocation centre. In order to asses the effect of multiple substitution at this site, we first considered those compounds that have two fixed hydrogen atoms at the -position of the phenyl group, which according to Hammett classification have crp(H) = 0.0, and the third phenyl group substituted at -position with H (compound 96 in Chart 6) OCH3 (compound 97 in... 

Ring substituents can have a considerable effect on the acidity of the system. In the 1,2,4-triazole series a 3-amino group decreases the acidity to 11.1, a 3-methyl group to 10.7, whereas a 3-phenyl group Increases the acidity to 9.6, and 3,5-dlchloro substitution to 5.2 (71PMH(3)1). 

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]. 

Two examples of steric effects deserve attention. In aryl complexes cis-Pt(PR3)2ArCl, introducing ort/io-substituents into the phenyl group slows down substitution considerably, as these block the position of attack (Figure 3.82). 

Phenyl or mixed alkyl/phenyl substituted silicon hydrides show similar reactivities to trialkylsilanes. Indeed, by replacing one alkyl by a phenyl group the effect on the hydrogen donating ability of SiH moiety increases only slightly. ... 

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