Infrared matrix-isolation spectra of acrylyl fluoride rotamers

Infrared spectra of acrylyl fluoride have been studied in the vapor phase and in neon, argon, and nitrogen matrices in the regions 200–4000 cm−1 and all fundamental vibrations have been assigned for the s-cis and s-trans rotamers. Isomerization frequency shifts of 19, 20, and 41 cm−1 are found for certain–OCF modes, though most vibrations show much smaller shifts. Many vapor phase band contours are complex due to the overlap of several modes; the matrix-isolation experiments clarify this data and in some instances provide intense fundamentals that are not detected in conventional sampling. The matrix isolation of large populations of both s-cis and s-trans rotamers suggests that there is a small potential energy difference between these two forms but that a large potential barrier hinders their interconversion. The results are consistent with the magnetic resonance study of Lin and Servis [J. Am. Chem. Soc. 94, 5794 (1972)] and their two data points, together with s-cis and s-trans C–C torsion frequencies, are used to estimate the first four coefficients in the C–C internal rotation potential energy function. Matrix-isolation experiments on 13C acetyl fluoride were performed and a new vibrational assignment found to be necessary for the acyl fluoride group. With this result the –OCF modes of acetyl fluoride and acrylyl fluoride closely parallel one another.