Using Equilibrium Isotope Effects To Detect Intramolecular OH/OH Hydrogen Bonds:  Structural and Solvent Effects

Abstract

A comparative (1)H NMR study of partially deuterated 1,3- and 1,4-diols has demonstrated that intramolecular hydrogen bonds of different geometry can give rise to equilibrium isotope shifts of opposite sign in hydrogen-bond-accepting solvents such as DMSO-d(6), acetone-d(6), and THF-d(8). The sign inversion is interpreted in terms of the ability of solvent molecules to form competitive intermolecular hydrogen bonds with the diol and in terms of the limiting chemical shifts for the interior and exterior hydroxyl groups. Deuterium is shown to prefer the intermolecular solvent hydrogen bond by 10.9 +/- 0.5 cal/mol for 1,4-diol 3 dissolved in DMSO-d(6) at room temperature. Pyridine-d(5) is shown to be capable of amplifying positive (downfield) isotope shifts measured in DMSO-d(6), in some cases by as much as a factor of 3. Its use is demonstrated for the assignment of the syn or anti relative configuration of 2,4-pentanediol and for the amplification of isotope shifts used to detect intramolecular hydrogen bonds in alpha- and beta-cyclodextrin. Studies in apolar solvents such as CD(2)Cl(2) and benzene-d(6) reveal that the isotope shift is negative (upfield) for all hydrogen bond geometries studied. Larger isotope shifts are measured in benzene-d(6), and a rationale for this amplification is presented. The use of apolar solvents is particularly useful for assigning the syn or anti configuration of 2,4-pentanediol.

Advanced Polymerization and Properties of Biobased High Tg polyester of Isosorbide and 1,4-Cyclohexanedicarboxylic Acid through in Situ Acetylation

“…The C5-OH is significantly less reactive than its exo-oriented counterpart, C2-OH. 9,44,45 This agrees with the results of Garaleh et al 43 as described above. To change this steric environment, PICD homopolyesters were synthesized using CHDA and ISB through acetylation, substituting the hydroxyl end group with an acetyl group using Ac 2 O.…”

NMR study of hydroxy protons of di‐ and trimannosides, substructures of Man‐9

“…For samples in H 2 O/acetone-d 6 solutions, additional conformational information in terms of hydrogen bonding and/or hydration can be obtained from observation of vicinal coupling constants, temperature coefficients, rate of exchange with water and NOEs of hydroxy protons. 14 -28 1 H or 13 C deuterium-induced differential isotope shifts 29,30 have been used to detect the existence of hydrogen bonding in aqueous solution of carbohydrates. In general hydroxy protons involved in hydrogen bonding are expected to have coupling constants that indicate a restricted rotation, relatively smaller temperature coefficients and a slower rate of exchange with water.…”

New NMR Tools for Characterizing the Dynamic Conformations and Interactions of Oligosaccharides

“…22 However, aprotic organic solvents significantly influence proton exchange rates and can abolish glycan binding to target molecules. 23 To solve this problem, a method was proposed for the evaluation of proton exchange of the hydroxy groups of the Lewis X trisaccharide in water, based on the line shape of the When hydroxy proton exchange between the isotopomers 13 COH/ 13 COD occurs in the slow-exchange regime, one can observe a deuterium-induced differential isotope shift for 13 C of 0.090.15 ppm.…”