Substituent effects on the proton affinities of selenoamides: A theoretical study

The proton affinities of nine substituted selenoamides for their chalcogen and nitrogen sites have been evaluated theoretically at the MP2/6-31++G∗//MP2/6-31+G∗ and B3LYP/6-31++G∗//B3LYP/6-31+G∗ levels. Similar calculations have been done for substituted thio- and oxo-amides. The proton affinities for the chalcogen site are slightly higher than the corresponding values for nitrogen sites in all the amides. The proton affinities for both chalcogen and nitrogen site decrease in the order of X as Se > S > O. The electron donating substituents increase the proton affinities while the electron withdrawing substituents decrease the proton affinities. The NBO analysis indicates that nN→πX-C∗ interactions are dominant in neutral molecule. The role of substituent becomes apparent in the protonated specie where electron delocalization of the type nY→πX-C∗ and nY→πC-N∗ also become operative.