The nature of intramolecular hydrogen bond in 2-nitromalonaldehyde

A simple, practical method for treating the proton tunneling in 2-nitromalonaldehyde (NO2MA) was used. A two-dimensional potential energy surface (PES) function, which couples OH stretching and in-plane bending modes, has been constructed for motions of the hydrogen atom by the aid of quantum mechanical calculations at the MP2/6-31G** level for a fixed skeleton geometry. This PES function was used to calculate energy levels, from which a tunneling splitting of 34.5 and 3.2 cm−1 was obtained for light and deuterated NO2MA, respectively, in excellent agreement with the experimental value of 35.0 ± 15.0 and 3.0 ± 0.02 cm−1, respectively. The double-well barrier height was predicted to be 46.4 kJ/mol with respect to the midpoint between the two adjacent minima of the hydrogen motions on the PES. The hydrogen-bond strength was estimated to be over 50 kJ/mol.