Nuclear magnetic resonance diffusion studies can be used to identify different compounds in a mixture. However, because the diffusion coefficient is primarily dependent on the effective hydrodynamic radius, it is particularly difficult to resolve compounds with similar size and structure, such as isomers, on the basis of diffusion. Differential solution interactions between species in certain solutions can afford possibilities for separation. In the present study, the self-diffusion of the three isomers of dihydroxybenzene (i.e., (1,2-) catechol, (1,3-) resorcinol, and (1,4-) hydroquinone) was studied in water, aqueous monohydric alcohols (i.e., ethanol, 1-propanol, tert-butanol), and aqueous ethylene glycol. These systems allowed the effects of isomerism and differential solvent interactions on diffusion to be examined. It was found that, while in aqueous solution these isomers had the same diffusion coefficient, in water-monohydric alcohol systems the diffusion coefficient of catechol differed from those of resorcinol and hydroquinone. The separation was found to increase at higher concentrations of monohydric alcohols. The underlying chemical reasons for these differences were investigated.

The structure and dynamics of hydrogen-bonded structures are of significant importance in understanding many binary mixtures. Since self-diffusion is very sensitive to changes in the molecular weight and shape of the diffusing species, hydrogen-bonded associated structures in dimethylsulfoxide-methanol (DMSO-MeOH) and DMSO-ethanol (DMSO-EtOH) mixtures are investigated using nuclear magnetic resonance (NMR) diffusion experiments and molecular dynamics (MD) simulations over the entire composition range at 298 K. The self-diffusion coefficients of DMSO-MeOH and DMSO-EtOH mixtures decrease by up to 15% and 10%, respectively, with DMSO concentration, indicating weaker association as compared to DMSO-water mixtures. The calculated heat of mixing and radial distribution functions reveal that the intermolecular structures of DMSO-MeOH and DMSO-EtOH mixtures do not change on mixing. DMSO-alcohol hydrogen-bonded dimers are the dominant species in mixtures. Direct comparison of the simulated and experimental data afford greater insights into the structural properties of binary mixtures.

Table 1 The relative diffusion difference as a percentage of o-PDA (D o-PD A ) compared to m-PDA (D m-PD A ) and p-PDA (D p-PD A ) in mixtures of water-MeOH with mole fraction x MeOH , measured at 298 K. x MeOH D o-PDA greater than D m-PDA (%) D o-PDA greater than D p-PDA

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Hydrogen‐bonded associated structures in DMSO–MeOH and DMSO–EtOH mixtures were studied using nuclear magnetic resonance diffusion experiments and molecular dynamics simulations over the entire composition range at 298 K. A direct comparison of the simulated and experimental data gives a greater insight into the structural properties of binary mixtures. More details can be found in the Full Paper by W. S. Price et al. on page 3814 in Issue 18, 2015 (DOI: 10.1002/cphc.201500670).