Benzoic acids pK, values

Although tellurophene-2-carboxylic acid (R = H) is the weakest acid in the series, it is stronger than benzoic acid. pK values of 5-substituted tellurophene-2-carboxylic acids correlate well with the five-membered ring 2-carboxylic acids, the p values are 1.41 (X = 0), 1.23 (X = S), 1.23 (X = Se), and 1.20 (X = Te) <1972J(P2)1738>. This sequence is indicative to the approximately equal transmittance of electronic effects of substituents across the five-membered heterocycle. 

The intrinsic delocalized (resonance) electrical-effect parameter. It represents the delocalized electrical effect in a system with zero electronic demand. cTg The electronic demand sensitivity parameter. It adjusts the delocalized effect of a group to meet the electronic demand of the system. cTj) A composite delocalized electrical-effect parameter which is a function of and cTg.Examples of constants are the ctr and ctr constants.The ctr constants, where k designates the value of the electronic demand rj, are also examples of Ojy constants. ctr a composite delocalized electrical-effect parameter of the ctd type with rj equal to 0.380. It is derived from 4-substituted benzoic acid pK values. 

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