The conformational behaviour of a series of monohydroxamic acids, p-RC,H,CONR'OH (R = Me, R' = H, Me; R = MeO, R' = H, Me; R = NO2, R' = H), and a series of dihydroxamic acids, (CH,),(CONR'OH), (n = 3-8, 10, R' = H and n = 7, R' = Me), in methanol, DMSO and chloroform and in the solid state has been examined using IR and NMR spectroscopy. X-Ray crystal structure determinations of p-MeC,H,CoNMeOH and the monohydrate of glutarodihydroxamic acid ( n = 3) together with ab initio molecular orbital calculations for several hydrated and unhydrated hydroxamic acids have been performed. Hydrogen bonding effects are shown to be important in both the solid state and solution. The cis(Z) conformation of the hydroxamate group(s) (CONHOH) is preferentially stabilized by hydrogen bonding with water molecules.
The orthorhombic Pccn structure of phase V of NH4NO a extends down to 5 K. The nonlinear behaviour of the lattice parameters as a function of temperature and the deformation of the ammonium molecule at 80 K indicate the onset of anharmonic coupling between the vibrational modes of the ammonium and nitrate molecules.We have recently proposed a new ordered structure for the low-temperature
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