Electrophilicities of 4‐Nitrobenzochalcogenadiazoles

Through the linear free energy relationship log k=sN (N + E), the electrophilicity parameters E of 4-nitrobenzochalcogenadiazoles 1 a and 1 b have been determined, at 20 °C, by kinetic investigations of their electrophilic addition reactions to a series of nitroalkyl anions 2 a-c in aqueous solution. The derived E-parameters of electrophiles 1 a (E=-12.80) and 1 b (E=-11.46) have been integrated into the electrophilicity scale established by Mayr. Interestingly the less activated compound (1 a) has an E value which is practically the same as that of the 1,3,5-trinitrobenzene (E=-13.19), the common reference aromatic electrophile. Mayr's approach was found to predict the rate constants for σ-complexation reactions of our electrophiles 1 a and 1 b with aniline and 4-chloroaniline in acetonitrile with a factor of 10−36. Good linear correlation (r2=0.9979) between the electrophilicity parameters E of 4,6-dinitrobenzochalcogenadiazoles 3 a-c and E values of their analogously 4-nitrobenzochalcogenadiazoles 1 a-c has been found and analysed. Furthermore, effect of basicity of nitronate anions 2 a-c on their nucleophilic reactivity has also been examined quantitatively on the basis of kinetic data. Imbalance effect is suggested to be responsible for the finding of an inequality between the Bronsted αelec and βnuc values.