Trapping of unstable molecular conformations in argon matrices: Gauche- and trans-1,2-difluoroethane

Huber-Wälchli, P.; Günthard, Hs. H.

doi:10.1016/0009-2614(75)80004-2

Cited by 49 publications

(26 citation statements)

References 6 publications

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“…An unassigned weak argon matrix band at 2994 cm -1 lies suspiciously close to this 2995 cm -1 gas-phase band, suggesting that its earlier assignment to 12G may be in error. 2 There is no binary 12G combination or overtone level as high as this. This suspicion is reinforced by the fact that the two fundamentals here, ν 7 (12T) and ν 11 (12G) both rise from gas phase to matrix, by 9 and 12 cm -1 respectively, whereas the 2995 cm -1 band apparently remains unchanged.…”

Section: Individual Compounds: Assignments and ν Is Ch Valuesmentioning

confidence: 92%

“…These are predicted at 1496 (B u ) and 1488 (A g ) cm -1 , the former being seen in the argon matrix at 1490 cm -1 . 2 Overtones from both of these can account for the polarized Raman line seen at 2995 cm -1 in the Raman spectrum, assuming an upward shift due to resonance with ν 1 (A g ), predicted below at 2931 cm -1 . An unassigned weak argon matrix band at 2994 cm -1 lies suspiciously close to this 2995 cm -1 gas-phase band, suggesting that its earlier assignment to 12G may be in error.…”

Section: Individual Compounds: Assignments and ν Is Ch Valuesmentioning

confidence: 98%

“…In at least one case, that of 1,2-difluoroethane, the assignment of observed bands to the different conformers is in dispute. 2,4,19 The principal tool enabling a correct analysis of this region of the spectrum has proven to be the use of spectra from partially deuterated materials giving the so-called isolated stretching frequencies, ν is CH, hopefully obtained from bands unaffected by Fermi resonances. 23 Unfortunately, problems associated with the preparation of isotopically labeled material appear to have inhibited such studies among the fluoroethanes except for the two cases of monofluoroethane 1,24 and 1,1,1,-trifluoroethane.…”

Section: Introductionmentioning

confidence: 99%

“…(2) The QC force field must yield reliable CH stretch/CH stretch interaction force constants f ′ which, along with G matrix terms dependent only on geometry, determine the spacings between different types of CH stretching motion.…”

Section: Introductionmentioning

confidence: 99%

“…b Computed infrared intensity in km mol -1 . c Frequencies observed in references(2,4,19). d νobs -νcalc: in parentheses, the calculated frequency.…”

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confidence: 99%

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Quantum-Chemical Studies of Fluoroethanes: Vibrational Assignments, Isolated CH Stretching Frequencies, Valence Force Constants, and Bond Length Relationships

McKean

2000

J. Phys. Chem. A

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Harmonic force fields for the series of fluoroethanes, derived from HF and B3LYP calculations with the 6-311G** basis set, are scaled individually for each molecule and for each type of CH bond. Reassignments are made in the νCH region with the aid of earlier correlations between CH bond length and six observed isolated CH stretching frequencies ν is CH. Eleven more ν is CH values are obtained from the spectra through the determination of scale factors. Estimation of the remaining three undetermined ν is CH values is discussed. Problems of assignment remain both in the νCH region and also between 1200 and 1000 cm -1 , which call for further study. Improved predictions are made of unobserved frequencies in the less abundant conformers of the 1,2-, 1,1,2-, and 1,1,2,2-fluoroethanes. νCH scale factors vary significantly according to the number of fluorine atoms attached to the same carbon and also to a lesser degree among those of the same type. Scale factors for other types of motion also vary both between molecules and also within a given molecule. Changes in the factor for torsional motion are particularly large. For the CH, CF, and CC bonds, unscaled valence force constants are given, and their relation to ν is CH, bond lengths, and bond length "offset" values is discussed. Evidence for variations in the latter is reviewed. An unscaled ν is CH value reflects very closely the corresponding CH stretching force constant in any of the groups methyl, methylene, and methine.

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Section: Individual Compounds: Assignments and ν Is Ch Valuesmentioning

confidence: 92%

Section: Individual Compounds: Assignments and ν Is Ch Valuesmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…b Computed infrared intensity in km mol -1 . c Frequencies observed in references(2,4,19). d νobs -νcalc: in parentheses, the calculated frequency.…”

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confidence: 99%

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