Journal of the American Chemical Society p. 718 - 726 (1988)
Update date:2022-08-11
Topics:
During, J. R.
Berry, R. J.
Wurrey, C. J.
The microwave spectrum of cyclopropyl isocyanate, c-C3H5NCO, has been recorded from 18.5 to 40.0 GHz.Two sets of a-type, R-branch transitions have been observed and assigned, on the basis of the rigid rotor model, to the trans and the cis conformers, which have the isocyanate moiety oriented in an s-trans or s-cis fashion, respectively, relative to the three-membered ring.In addition to the ground vibrational state transitions, lines due to two excited states of the CNC bend and four excited states of the asymmetric torsion for the trans conformer, as well as one torsional excited state for the cis form, have been assigned.The B and C rotational constants for the ground vibrational state of the trans and cis conformers are the following: B=1784.303 +/- 0.003, C=1716.133 +/-0.003 and B=2186.797 +/-0.010, C=2106.242 +/- 0.010 MHz, respectively.The values of the A rotational constants for both conformers were not well determined because the measured transitions are not very sensitive to these constants.From the relative intensity measurements in the microwave spectrum, the torsional frequency is estimated to be 24 cm-1 for the trans conformer and 14 cm-1 for the cis form.The dipol moment components determined from the Stark effect are /μa/=2.56 +/- 0.02, /μc/=0.71 +/- 0.03, and /μt/=2.65 +/- 0.02 D for the trans conformer and /μa/=2.720 +/-0.004, /μb/=0.17 +/-0.01, and /μt/=2.726 +/- 0.001 D for the cis conformer.With reasonably assumed sructural parameters for the cyclopropyl moiety and bond distances for the isocyanate group, estimates of the differences between the cis and trans conformers of the title molecule for the following parameters were made: r(C-N),
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