THE MICROWAVE SPECTRUM AND ROTATIONAL ISOMERISM OF BUTYRALDEHYDE

Abstract

The microwave spectra of the ground and two excited vibrational states of two rotational isomers of but yraldehyde have been assigned in the 8--36 GHz region. Both strong a- and b-type transitions are observed for the trans-trans form with all the heavy atoms in a plane of symmetry with all the CC and CH bonds staggered, whereas only strong b-type transitions are observed for the gauche-trans rotamer in which the dihedral angle between the CCC and the CCCHO plane is found to be $101^\circ \pm 2^\circ$. The effect of centrifugal distortion is significant in the latter conformation. The ground state rotational constants are A = 15069.42 MHz, B = 2555.98 MHz. C = 2278.61 MHz, for the trans-trans form; and A = 8508.49 MHz, B = 3588.78 MHz. C = 2028.60 MHz for the gauche-trans species. The dipole moments for both isomers have been determined and will be reported.