Torsional splitting and the four-fold barrier to internal rotation: The rotational spectra of vinylsulfur pentafluoride

Orellana, Walter; Stephens, Susanna L.; Pringle, Wallace C.; Groner, P.; Novick, Stewart E.; Cooke, Stephen A.

doi:10.1063/1.5050021

Cited by 5 publications

(1 citation statement)

References 17 publications

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“…1 Methyl torsion is regarded as a well understood LAM, 2 with the number of papers reporting the analysis of microwave spectra for molecules containing a methyl group recently being estimated to exceed 1000. 3 Microwave studies observe transitions between rotational states rather than observing the transitions between the torsional states directly but, nonetheless, constants describing the torsional motion, particularly the torsional potential, can be determined when fitting the observed line positions. 2,[4][5][6][7] Although there are many fewer studies of methyl torsion using electronic spectroscopy, studies of supersonically cooled gas phase samples have allowed torsional states to be observed directly (see Ito 8 and Breen et al 9 for early examples).…”

Section: Introductionmentioning

confidence: 99%

Evidence for widespread torsion–vibration interaction in substituted toluenes

Gascooke,

Lawrance

2023

Aust. J. Chem.

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The torsional constant (F) is a parameter extracted from spectroscopic analyses of molecules possessing a methyl group. Its value depends primarily on the methyl structure. Widely varying F values have been reported for substituted toluenes in their ground electronic state, first excited singlet electronic state or the ground electronic state of the cation. Conventionally, this variability is assumed to indicate significant changes in the methyl structure with substituent, its position on the ring and the electronic state. However, when the large amplitude methyl torsion interacts with other, small amplitude vibrations, this interpretation is misleading as the torsional states are shifted to lower energy, resulting in a reduced, ‘effective’ F being determined. We have observed coupling between methyl torsion and the low frequency, methyl group out-of-plane wag vibration in toluene, p-fluorotoluene, m-fluorotoluene and N-methylpyrrole, leading us to postulate that, since such motion will be present whenever the methyl group is attached to a planar frame, this type of interaction is widespread. This is tested for a series of substituted toluenes by comparing the methyl group structure calculated by quantum chemistry with the experimental torsional constants. The quantum chemistry calculations predict little variation in the methyl structure across a wide range of substituents, ring positions and electronic state. The wide variation in F values observed in experimental analyses is attributed to the torsion–vibration interaction affecting the torsional band structure, so that measured F values become ‘effective constants’. Comparisons between calculated and experimental torsional constants need to be cognisant of this effect.

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Section: Introductionmentioning

confidence: 99%

Evidence for widespread torsion–vibration interaction in substituted toluenes

Gascooke,

Lawrance

2023

Aust. J. Chem.

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On the experimental measurement of barriers to four-fold internal rotation in pentafluorosulfanyl-containing compounds: The microwave spectra of C3H5-SF5 and C4H7-SF5

Orellana

Stephens

Novick

et al. 2020

Journal of Molecular Spectroscopy

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Microwave spectra of a potential four-fold internal rotor, phenylsulfur pentafluoride

Signore

Falls

Stephens

et al. 2020

Journal of Molecular Structure

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We present the microwave spectra of the fourth molecule containing the four-fold rotor-SF 5 , phenylsulfur pentafluoride, cC 6 H 5-SF 4-F (PhSPF). The first three molecules in this series were vinylsulfur pentafluoride (VSPF), propen-1ylsulfur pentafluoride (PSPF) and buten-1-ylsulfur pentafluoride (BSPF). VSPF exhibited splitting into the A, E, and B torsional states with 10's of MHz between the torsional transitions. PSPF exhibited the torsional splitting with 10's of kHz between transitions. BSPF exhibited no torsional splitting. Likewise, PhSPF shows no torsional splitting in the spectra. This phenomenon is mostly explained by the differences in the values of the four-fold barrier to internal rotation, V 4 , in this series of molecules.

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Torsional splitting and the four-fold barrier to internal rotation: The rotational spectra of vinylsulfur pentafluoride

Cited by 5 publications

References 17 publications

Evidence for widespread torsion–vibration interaction in substituted toluenes

Evidence for widespread torsion–vibration interaction in substituted toluenes

On the experimental measurement of barriers to four-fold internal rotation in pentafluorosulfanyl-containing compounds: The microwave spectra of C3H5-SF5 and C4H7-SF5

Microwave spectra of a potential four-fold internal rotor, phenylsulfur pentafluoride

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