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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}
}
  • 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 methylurea, ethylurea, isopropylurea, t-butylurea and phenylurea using the B3LYP/DZVP2 and MP2/aug-cc-pVDZ methods. The analysis of alkylureas reveals cis and (less stable) trans isomers that adopt anti geometries, whereas syn geometries do not correspond to stationary points. In contrast, the analysis of phenylurea reveals that the lowest energy form at the MP2 level is a trans isomer in a syn geometry. The fully optimized geometries are in good agreement with crystal structure data,more » and PESs are consistent with the experimental dihedral angle distribution. Rotation about the C(sp2)-N bond in alkylureas and phenylurea is slightly more hindered (8.6-9.4 kcal/mol) than the analogous motion in the unsubstituted molecule (8.2 kcal/mol). At the MP2 level of theory, the maximum barriers to rotation for the methyl, ethyl, isopropyl, t-butyl and phenyl groups are predicted to be 0.9, 6.2, 6.0, 4.6 and 2.4 kcal/mol, respectively. The results are used to benchmark the performance of the MMFF94 force field. Systematic discrepancies between MMFF94 and MP2 results were improved by modification of several torsional parameters.« less
  • The authors measure the direct geminal and vicinal spinspin coupling constants between the C-13 nuclei of the phenyl group in the series of alkyl phenyl sulfides C/sub 6/H/sub 5/SR. It was shown that the variation in most of the discussed constants is determined by the ratio of the planar and orthogonal conformers. Linear relationships were obtained between the C-13-C-13 constants and the fractions of the planar conformer. The C-13-C-13 spin-spin coupling constants in the planar and orthogonal conformers of the compounds were calculated by means of empirical relationships.
  • 1-Vinylpyrroles, alkyl- and phenyl-substituted in the ring, are phosphorylated by phosphorus pentachloride in the ..cap alpha.. position of the pyrrole ring with the subsequent addition of the chlorophosphorane at the N-vinyl group with the formation of pyrrolo(1,2-a)-1,1,3-trichloro-4,1-azaphospholanium hexachlorophosphates. By treating the phosphorylation products with sulfur dioxide and triethylamine the authors synthesized pyrrolo(1,2-a)-1-oxo-1-chloro-4,1-azaphosphol-2-enes. The introduction of phenyl substituents into the nucleus of 1-vinylpyrroles or of alkyl substituents in the C/sup 2/ and C/sup 5/ positions is conducive to substitutive phosphorylation in the vinyl group and the formation of phosphorus-containing enamines. 1-Vinylindole and 9-vinylcarbazole are phosphorylated exclusively at the vinyl group. Hydrogenmore » 1, phosphorus 32, and carbon 13 NMR spectra are analyzed in detail.« less
  • The frontal analysis method was used to measure the adsorption isotherms of phenol, 4-chlorophenol, p-cresol, 4-methoxyphenol and caffeine on a series of columns packed with home-made alkyl-phenyl bonded silica particles. These ligands consist of a phenyl ring tethered to the silica support via a carbon chain of length ranging from 0 to 4 atoms. The adsorption isotherm models that fit best to the data account for solute-solute interactions that are likely caused by p-p interactions occurring between aromatic compounds and the phenyl group of the ligand. These interactions are the dominant factor responsible for the separation of low molecular weightmore » aromatic compounds on these phenyl-type stationary phases. The saturation capacities depend on whether the spacer of the ligands have an even or an odd number of carbon atoms, with the even alkyl chain lengths having a greater saturation capacity than the odd alkyl chain lengths. The trends in the adsorption equilibrium constant are also significantly different for the even and the odd chain length ligands.« less