Microwave, infrared, and Raman spectra, conformational stability, barriers to internal rotation, ab initio calculations, and vibrational assignment of 3-fluoro-2-methylpropene

Durig, J. R.; Qiu, Howard Z.; Durig, D. T.; Zhen, Mengzhang; Little, T. S.

doi:10.1021/j100160a024

Cited by 22 publications

(5 citation statements)

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“…27,28 Values of 1.74 and 1.89 kcal mol 1 were obtained for cis-and gauche-3-fluoro-2-methylpropene. 30 In the present study, the predicted methyl barrier (C 3v rotor attached to vinylic CH group) is fairly close to the previous theoretical and experimental values. 26 -30 A parallel scheme was also used for the TCT conformer (C 2v , Fig.…”

Section: Potential Surface Scansupporting

confidence: 90%

Vibrational analysis, conformational stability, force constants, barriers to internal rotations, RHF, MP2 and DFT calculations of trans,trans‐2,4‐hexadiene

Mohamed

Aly

2004

J Raman Spectroscopy

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Six conformers are proposed for the trans,trans-2,4-hexadiene (TTHD) molecule. Utilizing the 6-31G(d) and 6-311+G(d) basis sets at the levels of RHF, MP2 with full electron correlation and DFT-B3LYP, five conformers are found to be transition states, due to the calculated imaginary wavenumber(s). Accordingly, the totally symmetric TTT conformer where the two methyl groups are staggered to all trans vinylic hydrogen's (C 2h symmetry) is the stable conformer in the gaseous, liquid and crystalline phases. Aided by MP2(full)/6-311+G(d) geometric parameters, a chosen value of the kinetic parameter F = 6.11284856 was determined. Utilizing the observed band at 148 cm −1 in the far-infrared spectrum of the gas, a value of 1.41 ± 0.06 kcal mol −1 was obtained for the C 3v internal rotor (V 3 ), compared with 1.83 ± 0.07 kcal mol −1 predicted from a potential energy surface scan (1 kcal = 4.184 kJ). Aided by normal coordinate analysis and quantum chemistry (QC) calculations, the scaled quantum mechanical (SQM) force field was obtained employing five scaling factors for different types of vibrational motions. The scaled vibrational wavenumbers from both MP2(full) and B3LYP levels using the 6-31G(d) basis set provides an excellent approach to the observed fundamentals in either infrared or Raman spectra of the TTT conformer. Thus, confident vibrational assignments and potential energy distributions (PEDs) were provided for all fundamental modes of the TTT conformer. Moreover, the conformational stabilities, structural parameters, rotational constants, infrared intensities and Raman scattering activities are also reported. These results are discussed and compared with the experimentally determined values for some related conjugate systems when appropriate.

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Section: Potential Surface Scansupporting

confidence: 90%

Vibrational analysis, conformational stability, force constants, barriers to internal rotations, RHF, MP2 and DFT calculations of trans,trans‐2,4‐hexadiene

Mohamed

Aly

2004

J Raman Spectroscopy

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“…With the substitution of the chlorine atom at the 2-position there is stabilization of the cis conformer that is predicted by the ab initio calculations . On the other hand, substitution of a methyl group at the 2-position favors the gauche conformer, and the ab initio calculations indicate that the two conformers have nearly equal energies . The preliminary results for the molecule substituted with a methyl group on the 1-position indicate that the gauche conformer is favored.…”

Section: Discussionmentioning

confidence: 63%

Conformational Stability of 3-Fluoropropene in Rare Gas Solutions from Temperature-Dependent FT-IR Spectra and ab Initio Calculations

Veken¹,

Herrebout²,

Durig³

et al. 1999

J. Phys. Chem. A

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137

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The infrared spectra (3500−400 cm-1) of 3-fluoropropene (allyl fluoride), CH2C(H)CH2F, dissolved in liquid argon, krypton, and xenon have been recorded at various temperatures ranging from −180 to −65 °C. From these studies, the enthalpy difference between the more stable cis conformer and the high-energy gauche rotamer has been determined to range from 60 ± 8 cm-1 (718 ± 96 J/mol) in liquid xenon to 81 ± 1 cm-1 (969 ± 12 J/mol) in liquid argon. These values have been extrapolated utilizing a linear relationship between the Kirkwood function of the solvent and the enthalpy differences in the solvents to give a value of 130 ± 25 cm-1 (1.56 ± 0.30 kJ/mol) for the vapor. From the experimental enthalpy value, the gauche dihedral angle, torsional transitions for both rotamers, and better structural parameters, the potential function governing the conformational interchange has been recalculated. Ab initio calculations utilizing the 6-31G(d,p) and 6-311G(d,p) basis sets with electron correlation at the MP2 level predict the cis conformer to be the more stable rotamer, but from the MP2/6-311++G(d,p) calculation the gauche conformer is predicted to be more stable by 117 cm-1 (1.40 kJ/mol). By combination of the ab initio predictions of the structural parameters with the previously reported microwave rotational constants for 11 different isotopic species of both conformers, complete r o parameters have been obtained for both rotamers. The results of these structural parameter determinations are compared to those previously reported.

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“…7,8 The bonded interactions are interpreted in terms of a relatively simple three-component picture, including bond stretching, bond angle bending, and bond rotation. 7,8 Since rotational barriers are usually low enough to be overcome by the angular momentum of rotational thermal motion at room temperatures, [9][10][11][12][13] the bond rotation, in terms of torsion potential function, is therefore the most decisive factor in the determination of molecular conformations which are closely related to the transport properties and other dynamic properties. The torsion potential profiles or rotational barriers have been extensively investigated and evaluated through various experiments and theoretical calculations, 11,[14][15][16] however, only being expressed as torsion potential functions they can be applied to the molecular simulations.…”

Section: Introductionmentioning

confidence: 99%

New torsion potential expression for molecules without rotational symmetry

Yan

Lü

2008

The Journal of Chemical Physics

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A new torsion potential function for bond rotations without rotational symmetry is proposed. This function is composed of a few Gaussian-type terms each corresponding to an eclipsed conformation of the 1,2 substituents of the C-C bonds. Different from the truncated Fourier series or the truncated cosine polynomial, it is easy to determine how many terms are needed to represent any type of torsion potential barrier at a glance using the Gaussian-type function. It could also intuitively deduce the physical meaning of the expansion parameters of the new torsion potential function, which corresponds to the barrier height, the dihedral defining the eclipsed conformations, and the size of the substituents, respectively. The new torsion potential function is also applied to the 1, 2-substituted haloethanes with satisfactory results, where three Gaussian-type terms corresponding to the fully eclipsed and the partially eclipsed conformations are needed.

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Microwave, infrared, and Raman spectra, conformational stability, barriers to internal rotation, ab initio calculations, and vibrational assignment of 3-fluoro-2-methylpropene

Cited by 22 publications

References 0 publications

Vibrational analysis, conformational stability, force constants, barriers to internal rotations, RHF, MP2 and DFT calculations of trans,trans‐2,4‐hexadiene

Vibrational analysis, conformational stability, force constants, barriers to internal rotations, RHF, MP2 and DFT calculations of trans,trans‐2,4‐hexadiene

Conformational Stability of 3-Fluoropropene in Rare Gas Solutions from Temperature-Dependent FT-IR Spectra and ab Initio Calculations

New torsion potential expression for molecules without rotational symmetry

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