Glycolaldehyde Monomer and Oligomer Equilibria in
Aqueous Solution: Comparing Computational Chemistry and NMR Data
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Abstract
A computational
protocol utilizing density functional theory calculations,
including Poisson–Boltzmann implicit solvent and free energy
corrections, is applied to study the thermodynamic and kinetic energy
landscape of glycolaldehyde in solution. Comparison is made to NMR
measurements of dissolved glycolaldehyde, where the initial dimeric
ring structure interconverts among several species before reaching
equilibrium where the hydrated monomer is dominant. There is good
agreement between computation and experiment for the concentrations
of all species in solution at equilibrium, that is, the calculated
relative free energies represent the system well. There is also relatively
good agreement between the calculated activation barriers and the
estimated rate constants for the hydration reaction. The computational
approach also predicted that two of the trimers would have a small
but appreciable equilibrium concentration (>0.005 M), and this
was
confirmed by NMR measurements. Our results suggest that while our
computational protocol is reasonable and may be applied to quickly
map the energy landscape of more complex reactions, knowledge of the
caveats and potential errors in this approach need to be taken into
account