Can the substituent in the para position of anilide ion influence the N−···H–F → N–H···F− switching: a quantum chemical study

Abstract

The effect of substituents in the para position of anilide ion (An) on the N−···H–F → N–H···F− switching in X–An–HF (X = H, Me, CHO, CN, NO, F, NO2, OH and OMe) complexes was investigated by means of B3LYP and MP2 quantum chemical methods. To delve into the mechanistic details of the proton transfer process, potential energy curve and further geometrical parameters involved in H-bonding during the course of the proton transfer process were evaluated at the MP2/6-311++G(2d,2p) level of theory. The changes in H-bond strength because of variation of substituents were well accompanied by changes in formation energy of complexes, structural parameter, electron density, natural charge and charge transfer between subunits. For X = H, Me, CHO, CN, NO, F and NO2 substituents, our results at MP2/6-311++G(2d,2p) level showed that the minimum energy structures correspond to the N···HF H-bonded complexes without proton transfer occurring. On the other hand, for electron-donating substituents OH and OMe, proton is transferred from HF to anilide ion and the minimum energy structures are HNH···F− H-bonded complexes. The nature of HN−···HF and HN–H···F− interactions in complexes was characterized by means of atoms in molecules and natural bond orbital analyses.