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

Abstract

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 benchmarkmore » 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.« less

Authors:
;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
882584
Report Number(s):
PNNL-SA-47513
3565; 830403000; TRN: US200720%%351
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry A, 110(14):4678-4688; Journal Volume: 110; Journal Issue: 14
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ATOMS; BENCHMARKS; CRYSTAL STRUCTURE; ELECTRONIC STRUCTURE; GEOMETRY; ISOMERS; MODIFICATIONS; NITROGEN; POTENTIAL ENERGY; ROTATION; SULFUR; THIOUREA; THIOUREAS; TORSION; alkylthiourea; phenylthiourea; Environmental Molecular Sciences Laboratory

Citation Formats

Bryantsev, Vyacheslav, and Hay, Benjamin P. Conformational Preferences and Internal Rotation in Alkyl- and Phenyl-Substituted Thiourea Derivatives. United States: N. p., 2006. Web. doi:10.1021/jp056906e.
Bryantsev, Vyacheslav, & Hay, Benjamin P. Conformational Preferences and Internal Rotation in Alkyl- and Phenyl-Substituted Thiourea Derivatives. United States. doi:10.1021/jp056906e.
Bryantsev, Vyacheslav, and Hay, Benjamin P. Thu . "Conformational Preferences and Internal Rotation in Alkyl- and Phenyl-Substituted Thiourea Derivatives". United States. doi:10.1021/jp056906e.
@article{osti_882584,
title = {Conformational Preferences and Internal Rotation in Alkyl- and Phenyl-Substituted Thiourea Derivatives},
author = {Bryantsev, Vyacheslav and Hay, Benjamin P.},
abstractNote = {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.},
doi = {10.1021/jp056906e},
journal = {Journal of Physical Chemistry A, 110(14):4678-4688},
number = 14,
volume = 110,
place = {United States},
year = {Thu Apr 13 00:00:00 EDT 2006},
month = {Thu Apr 13 00:00:00 EDT 2006}
}