Molecular anisotropy of urea, CO(NH2)2, and of related compounds

Abstract

Abstract The magnetic anisotropy of urea has been measured and compared with that of the carbonate and nitrate groups. It does not appear that the hydrogen bonds contribute appreciably to the anisotropy; the latter indicates about the same degree of resonance in all three groups. The anisotropy of the refractivities is greater in urea than in the carbonate group, showing that the (NH2)- radical must be much more polarizable than the 0= ion, allowance being made for the interionic distances. Urea nitrate, urea oxalate, cyanuric acid dihydrate and anhydrous cyanuric acid all crystallize in layer structures, as shown by cleavage, X-ray data, magnetic and optical observations. The magnetic anisotropy of urea nitrate and urea oxalate is approximately additive, but that of cyanuric acid dihydrate is considerably larger than the additive value for three urea molecules, being comparable with that of other cyanuric ring compounds. Although the molecules in each layer must be joined together by hydrogen bonds, it does not follow that hydrogen bonds form the links between successive layers, since the layer to layer distance of 3.05 ± 0.10 A is characteristic even of cyanuric triazide, which contains no hydrogen bonds.