Quantum Mechanical and ^{13}C Dynamic NMR Study of 1,3-Dimethylurea
Conformational Isomerizations

Chambers, C. C.; Archibong, E. F.; Jabalameli, A.; Sullivan, R. H.; Giesen,
D. J.; Cramer, C. J.; Truhlar, D. G.

*J. Mol. Struct. (Theochem)*
**1998**, *425*, 61.

We present ^{13}C dynamic NMR results for relative free energies of
equilibrium structures and free energies of activation for conformational
transformations of 1,3-dimethylthiourea in aqueous solution, and we
compare the results to theoretical predictions. The latter are based on ab
initio gas-phase electronic structure calculations of the geometries,
dipole moments, and energies combined with semiempirical molecular orbital
calculations of the free energies of solvation in three different solvents.
The gas-phase electronic structure calculations were performed using
Moller-Plesset second-order (MP2) perturbation theory with a
correlation-consistent polarized valence-double-zeta basis set; we
calculated relative energies for the three minima *Z,Z*, *E,Z*,
and *E,E* and for
three transition states on the potential energy surface. The solvation
energy calculations were carried out using the SM5.4/A-aqueous,
-chloroform, and -organic solvation models; these solvation models are
based on semiempirical molecular orbital theory with class IV charges and
geometry-based first-solvation-shell effects. The relative energies of the
conformers and transition states are compared to experiment in water and
five organic solvents.

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