An NMR investigation of the importance of intramolecular hydrogen bonding in determining the conformational equilibrium of ethylene glycol in solution

Abstract

Although conformational analysis by NMR of ethylene glycol indicates generally strong preferences for the gauche conformation in solvents ranging from water to chloroform, the bulk of the NMR evidence indicates that intramolecular hydrogen bonding between the hydroxyl groups is unlikely to be a significant factor in determining that preference, except possibly in fairly non-polar solvents. The 'gauche effect' is clearly very important, especially in aqueous solution.

Zero-field nuclear magnetic resonance spectroscopy of viscous liquids

“…The profile is in qualitative agreement with the simulation obtained from the time-evolution of the density matrix for six spin-1/2 nuclei [5] evaluated with the values of the coupling constants obtained from HF NMR [25]. The simulated J-coupling spectra at 76 C, as shown in Fig.…”

“…1 suggests that all couplings to hydroxyl protons are averaged to zero by chemical exchange. The vicinal proton coupling, 2 J HH , has no observable effect on the spectrum [25].…”

“…Among ten non-equivalent isomers of EG with different dihedral angles in one C-C and two C-O torsion angles, theoretical calculations have shown that two gauche conformers with a C-C torsion angle at possible potential minima, 60 and 300 , are favorable rather than trans conformers with a torsion angle of 180 [27][28][29][30][31][32][33][34][35]. The two-bond J-couplings in 1 H NMR measurements support the predominant gauche state [19][20][21][22][23][24][25][26]. However, NMR studies of EG have been usually made in solution states [19][20][21][22][23][24][25][26] possibly due to the broadening of NMR spectra in neat EG, and the effect of intermolecular hydrogen bonding between EG molecules for the conformations remains insufficiently explored.…”

“…The two-bond J-couplings in 1 H NMR measurements support the predominant gauche state [19][20][21][22][23][24][25][26]. However, NMR studies of EG have been usually made in solution states [19][20][21][22][23][24][25][26] possibly due to the broadening of NMR spectra in neat EG, and the effect of intermolecular hydrogen bonding between EG molecules for the conformations remains insufficiently explored.…”

“…NMR has been utilized to investigate molecular dynamics [17,9,18] and conformational equilibria of polyalcohols [19][20][21][22][23][24][25][26]. Among ten non-equivalent isomers of EG with different dihedral angles in one C-C and two C-O torsion angles, theoretical calculations have shown that two gauche conformers with a C-C torsion angle at possible potential minima, 60 and 300 , are favorable rather than trans conformers with a torsion angle of 180 [27][28][29][30][31][32][33][34][35].…”