Effect of intermolecular =C–HO interaction on the crystal structure and vibrational properties of 2,6-dimethyl-4-nitropyridine N-oxide

The crystal structure of 2,6-dimethyl-4-nitropyridine N-oxide (DMNPO) has been determined at ambient temperature. The compound crystallizes as a monoclinic structure, space group P2/n, with 12 molecules per unit cell. The unit cell contains three non-equivalent formula units. The nitro group is not coplanar with the pyridine ring. Through a system of =C–HO hydrogen bonds the molecules are arranged into a two-dimensional network of layers parallel to the axc plane.The IR and Raman spectra, measured in the 3500–100 cm⁻¹ region at ambient temperature, are correlated with X-ray structural data. The assignment of IR and Raman bands is given. The appearance of characteristic vibrational features in the spectra of this compound and the observed shifts of the =C–H and N–O IR active stretching modes, when the sample is dissolved in CCl₄, is discussed in terms of the relatively strong =C–HO hydrogen bonds present in this crystal.