Conformational behaviour of hydroxamic acids: ab initio and structural studies

Abstract

The conformational behaviour of a series of monohydroxamic acids, p-RC₆H₄CONR′OH (R = Me, R′= H, Me; R = MeO, R′= H, Me; R = NO₂, R′= H), and a series of dihydroxamic acids, (CH₂)_n(CONR′OH)₂(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-MeC₆H₄CONMeOH 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.