Ab Initio Calculations on Halogen Bond Between N-Br and Electron-donating Groups

Ab initio calculations of complexes formed between N-bromosuccinimide and a series of electron-donating groups were performed at the level of MP2/Lanl2DZ* to gain a deeper insight into the nature of the N-Br halogen bonding. For the small complexes, H3C-Br…NH3 and H2N-Br…NH3, the primary calculation has demonstrated that the N-Br in H2N-Br…NH3 can form a much stronger halogen-bonding complex than the C-Br. A comparison of neutral hydrogen bond complex series reveals that the electron-donating capacities of the atoms decrease in the order, N > O > S; O(sp3) >0(sp2), which is adequate for the C-Br halogen bonding. Interaction energies, in conjunction with the geometrical parameters show that the affinitive capacity of trihalide anions X−3 with N-bromosuccinimide are markedly lower than that of the corresponding X− with N-bromosuccinimide, even lower than those of neutral molecules with N-bromosuccinimide. AIM analyses further confirmed the above results.