Dipole-dipole interactions between protons in a glucopyranose derivative have been studied by means of the nuclear Overhauser effect and by spin-lattice relaxation experiments. The Overhauser enhancement measurements utilize a new pulse technique which permits the saturating field to have any specified spectral density function so that finite frequency bands in the NMR spectrum can be irradiated. By this method, the dipolar interactions between the various pairs of protons are evaluated. In contrast, the dipolar relaxation of a chosen proton by all other protons in the sample has been determined by comparing the inversion-recovery rates after selective and nonselective 180· pulses. The relaxation measurements indicate that the relaxation in this molecule is purely dipolar in origin. The Overhauser enhancement measurements of one proton are used to determine the contribution to its relaxation from two neighboring protons and, from these results, information about the geometry of the pyranose ring is evaluated.4466

Abraham et al.* The term " skew conformation " is used here to denote a conformation analogous to the C, form of cyclopentane,l and the term " envelope conformation " to describe one analogous to the C, form of cyclopentane.1

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A detailed study has been made of both the ' H and 19F nuclear magnetic resonance (n.m.r.) spectra of a series of hexopyranosyl fluoride derivatives. Some of the ' H spectra were measured at 220 MHz. The lH spectral parameters define both the configuration and the conformation of each of these derivatives. Study of the 19F n.m.r. parameters revealed several stereospecific dependencies. The 19F chemical shifts depend upon, (a) the orientation of the fluorine substituent with respect to the pyranose ring and, (b) the relative orientation of other substituents attached to the ring; for acetoxy substituents, these configurational dependencies appear to be additive. The ~icinal'~F-'H coupling constants exhibit a marked angular dependence for whichJ,,,,, = ca. 24 Hz whilstJgouche = 1.0 to 1.5 HZ for JF,,He and 7.5 to 12.6 Hz for JF*,H~. Thegeminal I9F-'H couplings depend on the orientation of the substituent at C-2; when this substituent is equatorial JF,H is ca. 53.5 Hz and whenit is axial the value is ca. 49 Hz.Canadian Journal of Chemistry, 47, 1 (1969) During the past several years it has become apparent that the determination of the precise conformations of carbohydrate derivatives in solution, by proton magnetic resonance (p.m.r.) spectroscopy, is considerably more complex than was at first appreciated (1). Unfortunately, the confidence limit which can be placed on such determinations has been severely compromised by the lack of any independent, and generally applicable, check upon the accuracy of the p.m.r. method. A further shortcoming of this technique arises from the comparatively low sensitivity of most p.m.r. parameters with respect to changes in "11 correspondence should be addressed to this author.aRecipient of a MacMillan, Bloedel and Powell River Scholarship, 1965 and a NRCC Studentship, 1966. Present address: Forest Products Laboratory, S.W. Marine Drive, Vancouver 8, British Columbia. 3Present address: Department of Chemistry, Louisiana Staie University, Baton Rouge, Louisiana 70803, steric environment, which precludes the facile study of carbohydrate systems which are conformationally mobile.In principle, these inherent disadvantages of the p.m.r. method could be eliminated if a second "magnetic" nuclear species, were to be included in the molecule under study. Investigation of the nuclear magnetic resonance (n.m.r.) parameters of this second nuclear species could, in principle, afford an independent check on the geometry of the compound under investigation. This second nuclear species could thus be effectively utilized as a "stereospecific probe" and, in the event that its parameters were more sensitive to changes in steric environment than are p.m.r. parameters, it could, in effect, be used as an "amplifier" for studying conformational distortions and mobilities which might otherwise be overlooked in a p.m.r. study.For a variety of reasons, fluorine is an obvious choice for this second nuclear species. Thus, the natural abundance of the magnetic 19F isotope Can. J. Chem. Downloaded from www.nrc...