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Related Concept Videos

Conformations of Ethane and Propane02:18

Conformations of Ethane and Propane

In an organic molecule, free rotation about the carbon-carbon single bond results in energetically different conformers of the molecule. Due to this rotation, called the internal rotation, ethane has two major conformations — staggered and eclipsed.
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered ethane, the...
Conformations of Cyclohexane02:11

Conformations of Cyclohexane

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The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

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The Potential Energy Coefficients for Internal Rotation in CH(2)DSH and CHD(2)SH.

Quade1, Liu, Su

  • 1Department of Physics, Texas Tech University, Lubbock, Texas, 79409

Journal of Molecular Spectroscopy
|January 10, 2001
PubMed
Summary

This study determined potential energy coefficients for internal rotation in deuterated methanethiol isotopologues using the internal axis method. The research clarifies torsional state assignments, advancing our understanding of molecular dynamics.

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Area of Science:

  • Molecular Spectroscopy
  • Quantum Chemistry
  • Chemical Physics

Background:

  • Internal rotation in molecules is crucial for understanding conformational dynamics.
  • Deuterated methanethiol isotopologues (CH(2)DSH and CHD(2)SH) provide insights into isotopic effects on molecular structure.
  • Previous studies lacked definitive torsional state assignments for certain spectral series.

Purpose of the Study:

  • To determine the potential energy coefficients V(1), V(2), and V(3) for internal rotation in CH(2)DSH and CHD(2)SH.
  • To assign the torsional states for a previously ambiguous Q-branch spectral series.
  • To calculate nonrigidity coefficients for trans and gauche conformations.

Main Methods:

  • Application of the internal axis method (IAM) for analyzing rotational spectra.
  • Utilizing torsional differences from ground and excited states to refine potential energy coefficients.
  • Employing a fourth term, K(varsigma), 3(e(2))-2(o(2)), for torsional state assignment.

Main Results:

  • Potential energy coefficients were determined: V(1) = 4.54 cm⁻¹, V(2) = -9.36 cm⁻¹, V(3) = 440.50 cm⁻¹ for CH(2)DSH.
  • Potential energy coefficients were determined: V(1) = -4.12 cm⁻¹, V(2) = 8.23 cm⁻¹, V(3) = 439.65 cm⁻¹ for CHD(2)SH.
  • The torsional state assignment for the Q-branch series was confirmed as o(2) to e(2).

Conclusions:

  • The internal axis method successfully determined key potential energy coefficients for internal rotation in isotopologues.
  • This study resolved ambiguities in torsional state assignments, enhancing molecular spectral analysis.
  • Nonrigidity coefficients were obtained for both major conformations, providing further structural information.