Vibrational spectra and structure of 1,2-difluoroethane: G a u c h e–t r a n s conformers

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Abstract
Infrared and laser‐Raman spectra of 1,2‐difluoroethane (FH2CCH2F) have been recorded from 4000 to 50 cm−1. Whereas the Raman spectra were measured for all three physical states, the infrared data were recorded for the gaseous and crystalline phases. Spectral transitions associated with the predominant gauche conformer have been assigned with confidence on the basis of clearly defined infrared band contours and Raman depolarization ratios. Although several fundamentals have also been assigned for trans‐1,2‐difluoroethane, the majority of the normal modes associated with trans‐C2F2H4 appear to be unresolved or coincident with bands assigned to gauche‐C2F2H4. The magnitude of ΔH separating the two conformers was determined to be 1.98±0.08 kcal/mole by measuring the temperature dependence of the Raman bands assigned to the F–C–C–F bending modes for gauche (503 cm−1) and trans (461 cm−1) C2F2H4, respectively. An overall potential function describing the torsional barriers and ΔH will be discussed on the basis of the variable temperature data and the low frequency torsional transitions. The present study is consistent with an earlier electron diffraction study but disagrees with the conclusions advanced in a previous vibrational investigation of C2F2H4. These results will be reviewed in detail since the existent data is consistent with a predominant gauche conformer.

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