Molecular structure and vibrational spectroscopy of isoproturon

The crystal structure of isoproturon [N-(4-isopropylphenyl)-N′,N′-dimethylurea] has been determined: the compound crystallizes in the space group Pbca with unit cell parameters a=10.186(2) Å, b=11.030(2) Å, c=20.981(4) Å. The structure was solved and refined down to R1=0.0508 and ωR2=0.12470 for 3056 reflections. The crystalline molecular network of this pesticide is stabilized, as for many molecules of the same family, by π-π interactions but especially by a medium-strong N-H⋯CO intermolecular hydrogen bond (2.14 Å). The X-ray parameters were then compared with the results of DFT quantum chemical calculation computed with the gaussian 94 package. A tentative assignment of the ATR-FT-IR and Raman spectra was proposed supported by vibrational mode calculation and spectroscopic data on benzenic and urea derivatives available in the literature. The presence of a tight band around 3300 cm−1, which can be assigned to the NH bond stretching mode as well as the low frequency position of the amide I band at 1640 cm−1, sensitive to solvent polarity, confirms the existence of a quite strong intermolecular hydrogen bond between neighboring molecules in the crystal of isoproturon.