Treatment of aldehydo-sugars with 2,3-bis(hydroxyamino)-2,3-dimethylbutane gave the corresponding 1,3-dihydroxyimidazolidines. Oxidation of these compounds gave, successively, unstable, free radicals having a 3-hydroxyimidazolidine 1-oxyl structure, then stable, free radicals having a 2-glycosyl-2-imidazoline 3-oxide 1-oxyl structure, which were reduced to stable 2-glycosyl-2-imidazoline 1-oxyl compounds. The orientation of the two last-named series of compounds around the o bond between carbohydrate and heterocyclic residues that bears the radical centre is indicated by the value of the hyperfine coupling aH of the carbohydrate proton nearest to the nitrogenous heterocyclic residue. The study of numerous compounds of both series shows that the value of the hyperfine coupling depends greatly on the structure of the carbohydrate residue. A general explanation based on the preponderance of eclipsed forms and on the primary influence of steric hindrance due to the substituents of the carbohydrate residue is proposed. This study also gives some indirect information on the conformation of diamagnetic compounds that show Iittle sterical difference, and about which ¹H-n.m.r. spectroscopy does not provide useful information.