Microwave Spectroscopy Measurements of Rotational Spectra and DFT Calculations for Two Distinct Structural Isomers of 1,1′-Dimethylferrocene

Chakree Tanjaroon, Kristen S. Keck, Stephen G Kukolich

Research output: Contribution to journalArticle

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Abstract

Microwave spectra were obtained for two distinct structural isomers of 1,1′-dimethylferrocene, an eclipsed synperiplanar isomer (ψ = 0°, the E0 isomer), with A = 1176.9003(2) MHz, B = 898.3343(2) MHz, C = 668.7469(2) MHz, and an eclipsed synclinal isomer (ψ = 72°, the E72 isomer) with A = 1208.7117(14) MHz, B = 806.4101(12) MHz, and C = 718.7179(8) MHz. The b-dipole, asymmetric-top spectra of both structural isomers were measured in the frequency range of 5-12 GHz using a Flygare-Balle type of spectrometer. A very good fit to observed transitions, with small distortion constants, was obtained for the E0 conformer, indicating that this conformer is nearly rigid. The deviations obtained in a similar least-squares fit for the E72 confomer are significantly larger, indicating possible fluxional behavior for this conformer. In addition, 7 out of the 26 transitions observed for the E72 isomer conformer clearly exhibit very small splittings, giving further evidence for internal motion. DFT calculations for the different possible conformations of 1,1′-dimethylferrocene arising from rotation of one methyl cyclopentadienyl ligand relative to the other about the nominal C5 axis by an angle ψ (dihedral angle) were performed using the B3PW91 functional. The calculations converged and were optimized for five structures on this torsional potential energy surface corresponding to different dihedral angles ψ; three yielded energy minima, and two gave energy maxima, corresponding to transition states. The experimental results are in very good agreement with the results of the DFT calculations.

Original languageEnglish (US)
Pages (from-to)844-850
Number of pages7
JournalJournal of the American Chemical Society
Volume126
Issue number3
DOIs
StatePublished - Jan 28 2004

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Microwave spectroscopy
Microwaves
Least-Squares Analysis
Discrete Fourier transforms
Isomers
Spectrum Analysis
Ligands
Dihedral angle
Potential energy surfaces
Conformations
Spectrometers

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Microwave Spectroscopy Measurements of Rotational Spectra and DFT Calculations for Two Distinct Structural Isomers of 1,1′-Dimethylferrocene. / Tanjaroon, Chakree; Keck, Kristen S.; Kukolich, Stephen G.

In: Journal of the American Chemical Society, Vol. 126, No. 3, 28.01.2004, p. 844-850.

Research output: Contribution to journalArticle

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abstract = "Microwave spectra were obtained for two distinct structural isomers of 1,1′-dimethylferrocene, an eclipsed synperiplanar isomer (ψ = 0°, the E0 isomer), with A = 1176.9003(2) MHz, B = 898.3343(2) MHz, C = 668.7469(2) MHz, and an eclipsed synclinal isomer (ψ = 72°, the E72 isomer) with A = 1208.7117(14) MHz, B = 806.4101(12) MHz, and C = 718.7179(8) MHz. The b-dipole, asymmetric-top spectra of both structural isomers were measured in the frequency range of 5-12 GHz using a Flygare-Balle type of spectrometer. A very good fit to observed transitions, with small distortion constants, was obtained for the E0 conformer, indicating that this conformer is nearly rigid. The deviations obtained in a similar least-squares fit for the E72 confomer are significantly larger, indicating possible fluxional behavior for this conformer. In addition, 7 out of the 26 transitions observed for the E72 isomer conformer clearly exhibit very small splittings, giving further evidence for internal motion. DFT calculations for the different possible conformations of 1,1′-dimethylferrocene arising from rotation of one methyl cyclopentadienyl ligand relative to the other about the nominal C5 axis by an angle ψ (dihedral angle) were performed using the B3PW91 functional. The calculations converged and were optimized for five structures on this torsional potential energy surface corresponding to different dihedral angles ψ; three yielded energy minima, and two gave energy maxima, corresponding to transition states. The experimental results are in very good agreement with the results of the DFT calculations.",
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AB - Microwave spectra were obtained for two distinct structural isomers of 1,1′-dimethylferrocene, an eclipsed synperiplanar isomer (ψ = 0°, the E0 isomer), with A = 1176.9003(2) MHz, B = 898.3343(2) MHz, C = 668.7469(2) MHz, and an eclipsed synclinal isomer (ψ = 72°, the E72 isomer) with A = 1208.7117(14) MHz, B = 806.4101(12) MHz, and C = 718.7179(8) MHz. The b-dipole, asymmetric-top spectra of both structural isomers were measured in the frequency range of 5-12 GHz using a Flygare-Balle type of spectrometer. A very good fit to observed transitions, with small distortion constants, was obtained for the E0 conformer, indicating that this conformer is nearly rigid. The deviations obtained in a similar least-squares fit for the E72 confomer are significantly larger, indicating possible fluxional behavior for this conformer. In addition, 7 out of the 26 transitions observed for the E72 isomer conformer clearly exhibit very small splittings, giving further evidence for internal motion. DFT calculations for the different possible conformations of 1,1′-dimethylferrocene arising from rotation of one methyl cyclopentadienyl ligand relative to the other about the nominal C5 axis by an angle ψ (dihedral angle) were performed using the B3PW91 functional. The calculations converged and were optimized for five structures on this torsional potential energy surface corresponding to different dihedral angles ψ; three yielded energy minima, and two gave energy maxima, corresponding to transition states. The experimental results are in very good agreement with the results of the DFT calculations.

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