2 research outputs found
Mapping the Kinetic and Thermodynamic Landscape of Formaldehyde Oligomerization under Neutral Conditions
Density functional theory calculations,
including Poisson–Boltzmann
implicit solvent and free energy corrections, are applied to study
the thermodynamic and kinetic free energy landscape of formaldehyde
oligomerization up to the C<sub>4</sub> species in aqueous solution
at pH 7. Oligomerization via C–O bond formation leads to linear
polyoxymethylene (POM) species, which are the most kinetically accessible
oligomers and are marginally thermodynamically favored over their
oxane ring counterparts. On the other hand, C–C bond formation
via aldol reactions leads to sugars that are thermodynamically much
more stable in free energy than POM species; however, the barrier
to dimerization is very high. Once this initial barrier is traversed,
subsequent addition of monomers to generate trimers and tetramers
is kinetically more feasible. In the aldol reaction, enolization of
the oligomers provides the lowest energy pathway to larger oligomers.
Our study provides a baseline free energy map for further study of
oligomerization reactions under catalytic conditions, and we discuss
how this will lead to a better understanding of complex reaction mixtures
with multiple intermediates and products
Glycolaldehyde Monomer and Oligomer Equilibria in Aqueous Solution: Comparing Computational Chemistry and NMR Data
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