Molecular Structure of Isocyanic Acid, HNCO, the Imide of Carbon Dioxide

Isocyanic acid, HNCO, the imide of carbon dioxide, was prepared by reaction of stearic acid and potassium cyanate (KOCN) at 60 degrees C in a sealed, thoroughly dried reactor. Interestingly, its crystal structure, solved by X-ray single crystal diffraction at 123(2) K, shows a group subgroup relation for the NCO- anion to carbon dioxide: (for CO2, cP12, Pa (3) over bar, a = 5.624(2) angstrom, 150 K, C-O 1.151(2) angstrom; for HNCO, oP16, Pca2(1), a = 5.6176(9), b = 5.6236(8), c = 5.6231(7) angstrom, 123(2) K). Precise positions of H, N, C, and O were determined by DFT calculations with WIEN2k leading to interatomic distances C-O 1.17, C-N 1.22, N-H 1.03, and -N-H center dot center dot center dot N 2.14 angstrom, and the interatomic angle N-C-O 171 degrees.