Conformations of some dianhydrohexitols

Abstract

Proton magnetic resonance spectra of three known diastereoisomers 1,4:3,6-dianhydro-D-glucitol, 1,4:3,6-dianhydro-D-mannitol, 1,4:3,6-dianhydro-L-iditol, and their diacetyl and dimesyl derivatives have been analyzed. The coupling constants obtained have been utilized to determine the conformation of the five-membered rings. Constancy of the couplings between ring protons throughout the series of compounds indicates the existence of one conformation common to all, and this appears to be a composite of the C, and Cz forms. It is significant that intramolecular hydrogen bonding, which occurs in two of the three diastereoisomers, has little or no effect on ring conformation.Canadian Journal of Chemistry, 47, 2395 (1969) It is well known that the hexitols L-iditol, D-glucitol, and D-mannitol readily form 1,4:3,6-dianhydrides under acidic conditions (1). These 1,4:3,6-dianhydrides each have two free hydroxyl groups located at the C-2 and C-5 positions.From inspection of molecular models the 1,4:3,6-dianhydrohexitols have two nearly planar cis-fused five-membered rings in the form of a "V" with the hydroxyl groups at the C-2 and C-5 positions either inside or outside the "V" shaped wedge. As in other ring systems the configuration of a group inside the wedge is designated as endo whereas one outside the wedge is exo. In the L-iditol derivative 1 both hydroxyl groups are exo, in the D-mannitol derivative 3 both are endo, and in the D-glucitol derivative 2 the hydroxyl at C-2 is exo and that at C-5 is endo.The stereochemistry of these compounds has been discussed by Mills (2) and the order of stability of the three compounds as deduced from their ease of formation (3, 4), epimerization (5), and general chemical properties (6, 7) indicates that the presence of an exo substituent increases the stability of the ring to which it is attached, by virtue of the diminished opportunities for interaction between non-bonded substituents. Furthermore the faces of the rings inside the "V" are less accessible than the faces outside, so exo and endo isomers exhibit differences in reactivity in the direction determined by the steric requirements of the reaction in question (8, 9). The extent of intramolecular hydrogen bonding, as determined by infrared spectroscopy in this series of compounds (10) illustrates the influence of structure on such bonding. The C-2 and C-3, and C-4 and C-5 oxygen bonds in the iditol derivative are trans related as in L-threitan so that intramolecular bonding is precluded. A cis relation of the C-4 and C-5 oxygen bonds exists in the D-glucitol analogue permitting a single intramolecular hydrogen bond. In D-mannitol the C-2 and C-3, and C-4 and C-5 oxygen bonds are cis related; two intramolecular hydrogen bonds may occur and the absence of detectable absorption for free hydroxyl groups indicates the completeness of the hydrogen bonding.Correlation of nuclear magnetic resonance Can. J. Chem. Downloaded from www.nrcresearchpress.com by 52.36.4.81 on 05/11/18For personal use only.

Structure of 1,4:3,6-dianhydro-D-sorbitol, C6H10O4, at 100 K

“…Each ring may be described in terms of planes through four atoms -the two atoms which are common to the two five-membered rings, and the two atoms bonded to these; the fifth atoms are displaced from these planes by about 0.5 A (Camerman, Camerman & Trotter, 1965). However, interpretation of the IH NMR vicinal coupling constants in DIAN (Hopton & Thomas, 1969) does not result in definite conclusions about the actual conformation of the ring system. To facilitate the interpretation of 1H NMR data DIAN was studied by X-ray analysis.…”

Synthesis and structural characterization of block and random low molecular weight copolymers composed of L-lactic acid and isosorbide succinate moieties

“…4,22 The low average molar masses obtained for PLLA are associated with the relatively low purity of the monomer L-lactide used, which serves to the purpose of this study. Perego et al 21 also obtained PLLA with low average molar masses by using less pure L-lactide.…”

Circular Dichroism of Nitrate Esters: A Planar Symmetry Rule for the Nitrato Chromophore

“…measurements not to be significantly altered by intramolecular hydrogen bonding or esterification (28). The restricted nonplanar conformation of oxolan-Zone (6, 7) was established by microwave spectroscopy (29).…”

“…The nitrate esters were synthesized from thecorresponding chiral alcohols (Table 3) (7,24,(28)(29)(30)(31)(32) either with anhydrous nitric acid in acetic acid-acetic anhydride at 0" (23,24) or via the corresponding chloroformate and silver nitrate (25) and were purified by distillation (cu. 0.5 Torr) or chromatography on columns of silica gel developed with chloroform (26).…”