High-resolution infrared studies of perdeutero-spiropentane, C5D8

Abstract

Perdeutero-spiropentane (C 5 D 8) has been synthesized, and infrared and Raman spectra are reported for the first time. Wavenumber assignments are made for most of the fundamental vibrational states. Gas phase infrared spectra were recorded at a resolution (0.002 cm-1) sufficient to resolve individual rovibrational lines and show evidence of strong Coriolis and/or Fermi resonance interactions for most bands. However a detailed rovibrational analysis of the fundamental ν 15 (b 2) parallel band proved possible, and a fit of more than 1600 lines yielded a band origin of 1053.84465(10) cm-1 and ground state constants (in units of cm-1): B 0 = 0.1120700(9), D J = 1.51(3) x10-8 , D JK = 3.42(15) x10-8. We note that the B 0 value is significantly less than a value of B a = 0.1140 cm-1 calculated using structural parameters from an earlier electron diffraction (ED) study, whereas one expects B a to be lower than B 0 because of thermal averaging over higher vibrational levels. A similar discrepancy was noted in an earlier study of C 5 H 8 [1]. The structural and spectroscopic results are in good accord with values computed at the anharmonic level using the B3LYP density functional method with a cc-pVTZ basis set.

Combined Electron-Diffraction and Spectroscopic Determination of the Structure of Spiropentane, C5H8

“…The amplitude differences l 1,2 – l l,3 , l 1,8 – l 3,6 , and l 1,12 – l 1,13 were constrained at the Gaussian values. c HCH flap angle = angle between the HCH bisector and the C1–C2 bond. d R = [∑ i w Δ i 2 /∑ i w i ( s i I m, i (obsd) 2 ] 1/2 , where Δ i = s i I m, i (obsd) – s i I m, i (calc). e B 0H value from ref . B 0D value from ref . In computing B z D , the C–D bond length was assumed to be 0.004 A shorter than the C–H value, as suggested in ref . …”

“… e B 0H value from ref . B 0D value from ref . In computing B z D , the C–D bond length was assumed to be 0.004 A shorter than the C–H value, as suggested in ref . …”

“…In the present case of spiropentane, C 5 H 8 , both the normal and per-deutero isotopomers were examined and very accurate B 0 values were determined, 0.1394741(1) , and 0.1120700(9) cm –1 , respectively. For both isotopomers, the experimental values fall as expected between the DFT values of B e and B 0 and agree with the latter within 0.6%.…”

“…The B 0 rotational constants used in this work were obtained from the analysis of infrared spectra recorded with a resolution of about 0.002 cm –1 using a Bruker IFS 125HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory. Several vibration–rotation bands were analyzed, yielding the ground state B 0 values reported in ref and .…”

“…In recent papers we have reported the results of high-resolution infrared studies of several interesting carbon ring compounds of high symmetry, including radialene, propellane, − bicyclopentane, , and spiropentane − (Figure ). In each case, the molecules are of interest to structural chemists because of their high ring strain and, in the case of propellane, because of the very unusual axial bond.…”