¹H NMR study of the hetero‐association of non‐symmetrical diols with pyridine; GIAO/DFT calculations on diols

Abstract

The 1H NMR titration method is used to investigate the association of non‐symmetrical 1,2‐ and 1,3‐diols with pyridine in benzene. These diols give well‐defined titration curves for the two non‐equivalent OH protons, but it is not possible to determine individual association constants. Only the sum of the first association constants for the two protons and the product of the first and second association constants are accessible. The sum is significantly higher than that of the association constants of the corresponding primary and secondary alcohols, but close to an estimate based on symmetrical diols. The product leads to second association constants similar to those found for symmetrical diols. The sum of the chemical shifts of the associated and non‐associated OH protons in either 1:1 pyridine complex is higher than that of the shifts in the free diol and the 2:1 complex. These features are consistent with small cooperative effects, amounting to an average increase in the reaction free energy of 1.3 kJ mol−1 compared to monohydric alcohols. Infrared (IR) spectra of non‐symmetrical diols and quantum mechanical (QM) calculation of the energies and 1H NMR shifts of the OH protons in several conformers of propan‐1,2‐ and butan‐1,3‐diols indicate that both the primary and the secondary OH groups act as “donor” or “acceptor” in the free molecule. Gauche interactions in propan‐1,2‐diol enhance chemical shifts considerably less than does the intramolecular hydrogen bond in butan‐1,3‐diol. Copyright © 2011 John Wiley & Sons, Ltd.

On the importance of intramolecular hydrogen bond cooperativity in d‐glucose – an NMR and QTAIM approach

“…To make matters worse, there is currently no way of determining theoretically or even experimentally the association constants of such complexes. For symmetrical 1,2‐diols and 1,3‐diols, association constants can be determined for the formation of 1 : 1 and 1 : 2 diol/pyridine complexes by NMR titration against pyridine, but this approach fails for non‐symmetrical diols . Association constants were obtained, again by NMR titration, for a number of 1,2‐diol, 1,3‐diol and amido alcohol carbohydrate derivatives, but it is not clear how this result was achieved.…”

1H NMR study of the hetero‐association of unsaturated alcohols with pyridine

“…Because of self‐association the OH proton chemical shifts of alcohols and of diols, quoted in any database, are higher than the low‐concentration values. When pyridine is added to the solution of an alcohol in benzene and its concentration progressively increased, the OH proton signal moves downfield, broadens and in some cases loses its fine structure.…”

“…In the following, association constants are numbered in accordance with previous publications . For a monohydric alcohol, the association constant, K 3 , is given by Eqn : …”

“…[28,29] It was established by density functional theory/gauge including atomic orbitals (DFT/GIAO) calculations that IHB and/or gauche interactions between OH groups lead to significant enhancement of the nuclear magnetic resonance (NMR) shifts of the OH protons in diols . Related cooperative effects on hetero‐association with pyridine are small . In the case of unsaturated alcohols, analogous effects on the NMR shifts might again be expected, but there has been no systematic NMR spectroscopic study of such alcohols.…”

Solvation Structure of 1,3-Butanediol in Aqueous Binary Solvents with Acetonitrile, 1,4-Dioxane, and Dimethyl Sulfoxide Studied by IR, NMR, and Molecular Dynamics Simulation

“…12 The majority of the researches are the theoretical calculations, such as density functional theory (DFT). [11][12][13][14][15] The DFT calculations have suggested that all of the four isomers may form the intramolecular hydrogen bond between the two hydroxyl groups. In the gas state, the hydrogen bond of BDs is more stable in the order of 1,4-BD > 1,3-BD > 1,2-BD ≈ 2,3-BD.…”