Basicity of the aziridine, solvent and substituent effects: A theoretical study

Ab initio investigations of the protonation of the aziridine and the para-X-phenylaziridine (X = NO2, H and MeO) are carried out at the MP2 level of theory with the 6-31G∗ basis set. In gas phase the phenylaziridine is found to have a greater proton affinity than the aziridine. When the solvent effects are taken into account, a reverse behavior is observed in agreement with the experimental data. In addition, our calculations show that the electronic effects are transmitted through the phenyl cycle; a π-donor substituent located at the para position of the phenyl increases the proton affinity of the para-X-phenylaziridine. Conversely, a π-acceptor substituent decreases the proton affinity of the para-X-phenylaziridine.