Rotator, plane, Stark effect

Pochan, Baldwin and Flygare have analyzed the microwave spectra of cyclopropanone and the isotopic isomers 13Ci, 13C2, and 2,2-dideutero-cyclopropanone.63) The rotational transitions were determined by studying the Stark effect (the shifts and splittings of lines produced by an electric field). The type of transition observed for cyclopropanone was consistent with C v symmetry and the sum of the moments of inertia (/a + /b — Ic) suggested that all four protons are out-of-plane. These data eliminate such structural alternatives as the dipolar oxyallyl tautomer 82 and allene oxide 83. The electric dipole moment (fi ) was calculated to be 2.67 0.10 D, which corresponds to an average of those of acetone (2.93 D) 65> and formaldehyde (2.34D).6 )... 

The ANI permanent dipole moment has not yet been well established. Earlier dielectric constant measurements (at a temperature of 459 K in the gas phase) provided a value of = 1.53 D62 (in units of Debye, ID = 3.33564 x 10 3° Cm). An earlier study using the Stark effect determination from the rotational spectroscopy reported a smaller value, /r = 1.15 0.02 D for C6H5NH2 and /r = 1.13 0.02 D for C6H5ND238. However, an independent MW study evaluated the p., component at 1.07 D and did not detect any h-and c-type transitions in the MW spectra37. More recent MW studies43 using also Stark effects in gas-phase electronic spectra pointed out that the values determined from MW spectra are actually the a-axis projection of the dipole moment. Therefore, the in-plane component of the dipole moment can be established as p.,(,Y0) = 1.13 D. 

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