Conformational Preferences and Internal Rotation in Alkyl- and Phenyl-Substituted Thiourea Derivatives

Journal Article · Thu Apr 13 04:00:00 EDT 2006 · Journal of Physical Chemistry A, 110(14):4678-4688

DOI:https://doi.org/10.1021/jp056906e· OSTI ID:882584

Bryantsev, Vyacheslav; Hay, Benjamin P

Potential energy surfaces (PES) for rotation about the N-C(sp3) or N-C(aryl) bond and energies of stationary points on PES for rotation about the C(sp2)-N bond are reported for methylthiourea, ethylthiourea, isopropylthiourea, t-butylthiourea, and phenylurea, using the MP2/aug-cc-pVDZ method. Analysis of alkylthioureas shows that conformations, with alkyl groups cis to the sulfur atom are more stable (by 0.4 to 1.5 kcal/mol) than the trans forms. All minima adopt anti configurations with respect to nitrogen pyramidalization, whereas syn configurations are not stationary points on the MP2 potential surface. In contrast, analysis of phenylthiourea reveals that a trans isomer in a syn geometry is the global minimum, whereas a cis isomer in an anti geometry is a local minimum with a relative energy of 2.7 kcal/mol. Rotation about the C(sp2)-N bond in alkyl and phenyl thioureas is slightly more hindered (9.1-10.2 kcal/mol) than the analogous motion in the unsubstituted molecule (8.6 kcal/mol). The maximum barriers to rotation for the methyl, ethyl, isopropyl, t-butyl and phenyl substituents are predicted to be 1.2, 8.9, 8.6, 5.3, and 0.9 kcal/mol, respectively. Corresponding PESs are consistent with the experimental dihedral angle distribution observed in crystal structures. The results of the electronic structure calculations are used to benchmark the performance of the MMFF94 force field. Systematic discrepancies between MMFF94 and MP2 results were improved by modification of selected torsion parameters and one of the van der Waals parameters for sulfur.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 882584
• Report Number(s): PNNL-SA-47513; 3565; 830403000
• Journal Information: Journal of Physical Chemistry A, 110(14):4678-4688, Journal Name: Journal of Physical Chemistry A, 110(14):4678-4688 Journal Issue: 14 Vol. 110
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ATOMS
BENCHMARKS
CRYSTAL STRUCTURE
ELECTRONIC STRUCTURE
Environmental Molecular Sciences Laboratory
GEOMETRY
ISOMERS
MODIFICATIONS
NITROGEN
POTENTIAL ENERGY
ROTATION
SULFUR
THIOUREA
THIOUREAS
TORSION
alkylthiourea
phenylthiourea