Electrophilicities of 4‐Nitrobenzochalcogenadiazoles

Through the linear free energy relationship log k = s N ( 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 ( r 2 =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 Brønsted α elec and β nuc values.