Insight into the Effects of Electrostatic Potentials on the Conversion Mechanism of the Hydrogen-Bonded Complexes and Carbon-Bonded Complexes: An Ab Initio and Quantum Theory of “Atoms in Molecules” Investigation

[Image: see text] Carbon bond and hydrogen bond are common noncovalent interactions; although recent advances on these interactions have been achieved in both the experimental and computational aspects, little is known about the conversion mechanism between them. Here, MP2 calculations with aug-cc-pVDZ basis set (aug-cc-pVDZ-pp for element Sn) were used to optimize the geometric configurations of the hydrogen-bonded complexes MH(3)F···HCN (M = C, Si, Ge, and Sn), carbon-bonded complexes HCN···MH(3)F (M = C, Si, Ge, and Sn), and transition states; the conversion mechanism between these two types of interactions has been carried out. The molecular electrostatic potential, especially the σ-hole, is directly related to the flatten degree of intrinsic reaction coordinate (IRC) curve. The energy barriers from the hydrogen-bonded complexes to the carbon-bonded complexes are 6.99, 7.73, 10.56, and 13.59 kJ·mol(–1). The energy barriers from the carbon-bonded complexes to the hydrogen-bonded complexes are 4.65, 7.81, 9.10, and 13.04 kJ·mol(–1). The breakage and formation of the bonds along the reaction paths have been discussed by the topological analysis of electronic density. The energy barriers are obviously related to the width of the structure transition region (STR). For the first derivative curve of IRC energy surface versus reaction coordinate, there is a maximum peak and a minimum peak, reflecting the structural transition states in the ring STRs.