The hydration of formic acid and acetic acid

Abstract

Formic and acetic acid share the unique feature, among carboxylic acids, of crystallising in the form of long chains, containing both O-H• • •O and C-H• • •O hydrogen bonds. We have performed a neutron diffraction study of the pure acids and of three mixtures of acid and water (2:1, 1:1 and 1:2). The data from the SANDALS diffractometer at ISIS have been modelled using the Empirical Potential Structure Refinement code, which is able to reproduce a set of configurations compatible with the experimental data. The relative importance of the hydrogen bonds present in the solution is assessed based on geometrical criteria: bond length and directionality as well as number of bonds. At all concentrations, the carbonyl oxygen on the carboxylic group is the most active site for strong hydrogen bond. The tendency to establish direct interactions between acid molecules in the presence of water is reduced for acetic acid by a larger degree than for formic acid. The overall tendency is for a greater number of hydrogen bonds being formed when the solution is more diluted. The availability of good quality structural data on the liquid states is of great importance for the understanding of spectroscopic experiments and for benchmarking both classic molecular dynamics and ab initio simulations. The results provide a springboard to more realistic models of aerosol formation, which is greatly needed for better understanding of clouds formation processes.

On the solvation of the phosphocholine headgroup in an aqueous propylene glycol solution

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Neutron diffraction experiments have been used to study an aqueous solution of 30 mol% PG, containing 200 mM of 1,2-dipropionyl-sn-glycero-3-phosphocholine (C 3 -PC). The neutron diffraction experiments were performed on the SAN-DALS diffractometer at the ISIS neutron facility, UK.…”

On the structure of prilocaine in aqueous and amphiphilic solutions

“…Neutron diffraction with isotopic substitution (NDIS) is a technique by which the structure of hydrogen containing liquids and solutions can be measured directly. 10,15,[17][18][19][20][21][22][23][24][25][26][27][28][29] The use of neutrons as a probe for hydrogen containing solutions exploits the different neutron scattering intensities for H versus D. 30 Neutron diffraction measurements give the average structure in solution in reciprocal space as a structure factor F(Q), where…”

“…Empirical potential structure refinement is a Monte Carlo based simulation specifically designed to model the structure of liquids and other disordered materials. 32 EPSR is a technique which has been used in combination with NDIS measurements to determine the local structure of a variety of molecules in solution, 10,15,[20][21][22][23][24][26][27][28]33 and is unique as it uses a set of measured diffraction data as a constraint for resultant computational model. By beginning with a set of starting potentials, Lennard-Jones and appropriate charges in the present work, these potentials are iteratively refined until the molecular structure is consistent with the measured F(Q) data.…”

A promising azeotrope-like mosquito repellent blend

“…Several investigators have studied the structure of carboxylic acids in the liquid state 16 , 17 . Radial distribution functions of nonanoic acid, depicted in Fig.…”