Theoretical calculations of the molecular properties of maleimide and its dimer

B3LYP theoretical calculations with 6-31++G(d,p) basis set have been performed to study the infrared spectrum of maleimide and its dimer. Our calculations have shown that the dimer formation leads to a binding energy of 44.0 kJ mol−1 involving two intermolecular hydrogen bonds between the amide hydrogen and a carbonyl group of two neighboring maleimides. This value is essentially due to the electrostatic interaction term. Our calculations have also revealed the vibrational changes, in terms of frequencies and IR intensities, after dimer formation. The most affected modes are associated with the NH stretching and in-plane bending bands. This behavior can be adequately interpreted by the hydrogen atomic charge and NH charge-flux based on the modified charge–charge flux-overlap model for infrared intensities. The B3LYP frequency shifts are in very good agreement with the experimental ones.