Structure and microwave spectrum of the 2-cyano-2-propyl radical

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Virginia Polytechnic Institute and State University

The rotational spectra of the 2-cyano-2-propyl and d⁶-2·cyano-2-propyl radicals were observed using a Stark modulated spectrometer. The radicals were generated in the gas phase by UV irradiation of sublimed azoisobisbutyronitrile. They were detectable in the cell for approximately one hour. Thirty-three transitions were assigned for (CH₃)₂CCN and twenty-one for (CD₃)₂CCN. The rigid rotor rotational constants determined by calculation of the hypothetical unsplit rotational transitions are A=8276.7, B=3919.7, C=2751.5Mhz for (CH₃)₂CCN and A=6241.3, B=3490.7, C=2372.6Mhz for (CD₃)₂CCN.

A program to calculate the fine splittings and hyperfine splittings due to the ¹⁴N nucleus and six protons was written. The spin rotation constants determined for the two species were Eaa=-69.9, Ebb=-36.1, Ecc=2.7Mhz and Eaa=-55.4, Ebb=-32.6 Mhz for (CH₃)₂CCN and (CD₃)₂CCN respectively. The hyperfine coupling constants for ¹⁴N are identical for both isotopic species and were found to be Taa=-17.2, Tbb=-17.1 and Tcc=34.4 Mhz. The proton and deuteron hyperfine splittings were not resolved. The structural parameters determined from an <r₀> fit of the moments are rCN=1.18A, rCC=1.42A, rCMe=1.50A and CCMe=119.3°. The C₄N skeletal framework was found to be planar.