# THE CONFORMATION AND INTERNAL ROTATION BARRIER IN BENZYL FLUORIDE

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 Title: THE CONFORMATION AND INTERNAL ROTATION BARRIER IN BENZYL FLUORIDE Creators: Bohn, Robert K.; Sorenson, Sterling A.; True, Nancy S.; Brupbacher, Thomas; Gerry, Michael C. L.; Jaeger, Wolfgang Issue Date: 1996 Publisher: Ohio State University Abstract: The rotational spectrum of benzyl fluoride is extremely dense when observed on a static gas sample with a Stark-modulated spectrometer. An unambiguous assignment was not found. Although the spectrum is considerably simplified in a pulsed-jet Fourier transform spectrometer, it is still remarkably rich and complex. Benzyl fluoride is nearly prolate ($K = -0.86$) and the $a$-type transitions were easily identified and assigned. Many of the $a$-type transitions occur as unsymmetrical doublets with splittings of the order of tens of kHz and intensity ratios about 4/1. $c$-Type transitions also were identified, some of which show splittings up to 5 MHz. The spectrum has been accounted for with a model including a low. Barrier to internal rotation with an observable tunnelling splitting such that $a$-type selection rules allow transitions only between levels of the same symmetry, and $c$-type selection rules only between levels of different symmetry. Using different sets of parameters for the two species and a constants energy difference between their rotational energy levels, 150 transitions were fit to 10 kHz with an energy difference of 3.4 MHz between the two different symmetry species. We are continuing the analysis using a hamiltonian which explicitly includes internal rotation of a $C_{2v}$ top. The observed value of $P_{cc}$, 16.89 amu-$A^{2}$, and the fact that $c$-type and not $b$-type transitions are observed unambiguously define the conformation of benzyl fluoride as that with the plane containing the C-C-F chain orthogonal to the benzene ring. Description: Address Sorenson and True: Dept. of Chemistry, U. of California, Davis, CA 95616 Author Institution: Dept. of Chemistry, U. of Connecticut; Dept. of Chemistry, U. of California; Dept. of Chemistry, U. of British Columbia; Dept. of Chemistry, U. of British Columbia; Dept. of Chemistry, U. of Alberta URI: http://hdl.handle.net/1811/13452 Other Identifiers: 1996-MF-14