Hammett relationships for

Table 8.6 Hammett Relationships for Quantifications of Aromatic Substituent Effects on the Toxicity of Various Acids ...

The reactivity of coordinated nitriles towards nucleophiles, and electrophiles when deprotonated, has been of major interest. Addition of OH- to the nitrile carbon occurs readily in alkaline solution, kobs = oh[OH-]) and the rate is increased some 106—107 times by coordination (equation 24).176177 k0H has values of 1-50mol-1 dm3 s 1 for R = alkyl177 [e.g. 3.4 (Me) 35 (CH=CH,)j and varies over a wider range for substituted benzonitriles following a Hammett relationship.For 2-cyanoben-zonitrile addition of one equivalent of OH is followed by intramolecular amidine formation on treatment with further alkali (29), or by rearrangement in acid and hydrolysis to the diamide (31), or cyclization to the alternative amidine isomer (32 Scheme 17).179 The alkaline hydrolysis of the... 

Among benzene derivatives, halogen-substituted compounds have been extensively studied and in the structure-reactivity studies " carried out on the reaction of OH and SO with the ortho and meta isomers of dichloro and dibromobenzenes and mono-bromotoluenes, the formation of substituted hydroxycyclohexadienyl radical was observed to be the major reaction channel. The bimolecular rate constants obtained for the reaction of OH with substituted halobenzenes are in the range (1.7 to 9.3) x 10 dm mol s. The rate constants obtained are found to follow the Hammett relationship for the reaction of OH with substituted halobenzenes and the p was found to be -0.5, indicating that OH radicals react by addition to the benzene ting. 

The use of a and a values of —0.34 and 0.42, respectively, for the ring NH group (replacement of a ring CH=CH), in conjunction with the Hammett relationship for pyridines, permits the prediction with reasonable... 

The Hammett relationship for the acid-catalysed hydrolysis of ethyl benzoates has negligible slope so that the inductive and resonance (7 ) effects for the acid-catalysed reaction are deduced to be negligible. Equation (7) thus reduces to Equation (12) from which the value of 5 may be determined. 

Using data from Table 1 plot the Hammett relationship for the alkaline hydrolysis of ethyl benzoates and explain the deviations from the linear regression. 

Y. Yukawa and Y. Tsuno, Resonance Effect in Hammett Relationship, in. The Modified Hammett Relationship for Electrophilic Reactions, Bull. Soc. Chem. Japan, 1959, 32, 971. 

Table 1 Some Hammett relationships for dissociation constants (...

Buschmann et al. have described a paper concerning the linear free energy relationships in the Patemo-Biichi reaction [148]. In this paper, an attempt was made to correlate AG with the free energy of the ground state conformers for cyclohexanol derivatives. No Hammett relationship for different aromatic substituents was observed, as the effect that this group has on the reaction is predominantly steric in nature, meaning that any effects on the selectivity of the reaction are derived purely from the auxiliary, Aux. For the photoreaction between 97... 

Fig. 8. Hammett relationship for the alkaline hydrolysis of ethyl benzoates.

Table 2.6 Substituent and Reaction Constants of the Hammett Relationship for Some Reactions...

Group contributions or additivity principle Extrathermodynamic relationships between rate and equilibrium parameters Poianyi and Brpnsted relations Hammett relationship for dissociation constants... 

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