THE MICROWAVE SPECTRUM OF $PROPIONALDEHYDE^{*}$

Abstract

The microwave spectrum of propionaldehyde $(CH_{3}CH_{2}CHO)$ has been examined in the region 8,000--35,000 mc. Rotational transitions have been assigned for two different conformations. The moments of inertia of one of these agree quite well with those predicted for a cis conformation, in which all heavy atoms lie in a plane. Here $^{1}/_{2} (I_{a} + I_{b} - I_{0}) = 3.093$ amu {\AA}$^{2}$ is observed compared with 3.075 amu {\AA}$^{2}$ calculated for four out of plane hydrogen atoms. For the second conformation, a-type R branch lines were assigned. Additional aspects of this problem will be discussed.