Radicals as hydrogen bond acceptors

The ability of carbon radicals to act as hydrogen bond accepters has been evaluated using ab initio theoretical methods. A hybrid Hartree-Fock Density Functional Theory based method (B3LYP), Moller-Plesset at the second perturbation order (MP2), and Quadratic CI methods that include single and double excitation (QCISD), have been used. The complexes formed by four radicals CH3(d), C2H4(t). (CH3)(2)C(t) and (CH3)(3)C(d)] with four standard hydrogen bond donors [FH, H2O, HCN and H3N] have been studied and their geometry, interaction energy, and electronic properties, within the Atoms in Molecules (AIM) methodology framework have been analyzed. The energy and geometry results show that the studied radicals are poor hydrogen bond (HB) accepters and the strength of the HBs qualitatively correlates with the molecular electrostatic potential (MEP) minimum of the isolated radicals. The atomic partition of different properties using the AIM methodology indicates that HBs complexes involving radicals behave differently to other HBs formed between neutral molecules.