LOW-FREQUENCY INFRARED SPECTRA OF BUTADIENE AND SOME DERIVATIVES

Author Institution: Molecular Spectroscopy Section, National Bureau of StandardsThe infrared spectra of 1,3 butadiene and several derivatives (including fluoroprene, isoprene, and chloroprene) have been investigated in the $250-600 cm^{-1}$ region in an effort to establish the low-frequency skeletal modes. The lowest in-plane fundamental in butadiene itself has been located at $303 cm^{-1}$; the analogous fundamental in the derivatives falls between 250 and $290 cm^{-1}$. The C-C single bond torsional fundamental in fluoroprene is found to be $156 cm^{-1}$ from the microwave spectrum, and probably has a similar frequency in the other compounds. The correlation of the other skeletal bending modes will be discussed. The $A_{u}$ fundamental of butadiene at $525 cm^{-1}$ shows well-resolved rotational structure which confirms the planar trans conformations of the molecule