Hammet-equation

The bipyridines are dibasic, and the two acid dissociation constants Ki and K2, for all the bipyridines have been determined. Typical values are recorded in Table I. There has been considerable interest in the first dissociation constants Ki of 2,2 -bipyridine and substituted 2,2 -bipyridines because of their use as metal complexing agents. In general, the order of relative basic strengths of derivatives of 2,2 -bipyridine is as expected. Electron-attracting substituents reduce the basicity, whereas electron-donating substituents increase the basicity of the molecule. " The dissociation constants of several substituted bipyridines correlate well with the Hammet equation. 2,2 -Bipyridines with an electron-donating substituent at position 4 are monoprotonated at N-1 and not at... 

Reaction constants p in the Hammet equation describing the influence of the substituents in the phenyl ring of 2-arylbenzoxazoles, 2-arylbenzoth-iazoles (68MI2), and 2-arylbenzotellurazoles are approximately the same value, indicating a similar mechanism of expressing the electronic effects of substituents at the nitrogen atom in different benzazoles. 

H-abstraction intramolecular, 378 Half-value concentration, 181 Half-band width, 69 Half quenching concentration, 173 Hamiltonian operator, 65 perturbing, 67 Hammet equation, 110 He-Ne laser, 318 Heavy atom perturbation, 70 external, 145 intermolecular, 71 intramolecular, 71... 

The pKa value of 3-nitro-l,5-naphthyridine is 0.63. The ionization constants for protonation at N-l (pAT,) and N-5 (p/O) of 3-nitro-l,5-naphthyri-dine are pKt = 0.98 and p/C = 0.48 and for 3-nitro-l,5-naphthyridin-2(lH)-one (pKa = 0.26) p/C, = 6.35 and pK5 = 0.67 were calculated using the modified Hammet equation. It was concluded by comparison of these results that protonation takes place at the ring-nitrogen in position 5 yielding 166a and 166b respectively (77KGS965). 

Hammet equation applied to intra molecular H bonded compounds. 

The negative value of p in the Hammet equation for aryl alkyl ketones arises from the presence of a positively charged reaction center in the transient state. 

Figure 8.7 Correlation between the base-catalyzed rate of hydrolysis of phenyl benzoates and the of the phenolic leaving group. The pAT values derived from the Hammet equation for phenols.

C.D. Johnson, The Hammet Equation, Cambridge University Press, 1973. 

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