ROTATIONAL SPECTRUM OF TWO CONFORMERS OF n-BUTYRALDEHYDE

Abstract

Following on the previous work of $Lee et. al^{-1}$, further experiments have been carried out on $CH_{3}CH_{2}CH_{2}CHO$ using a pulsed-nozzle Fourier transform microwave spectrometer. The four singly substituted $^{13}C$ and the $^{18}O$ isotopomers were assigned in natural abundance for both conformers. With this information a definitive structural determination could be performed. The two assigned conformers are drawn below. The trans-tran conformer, the lower in energy, is heavy-atom planar and exhibits a strong a-type spectrum with weaker >b-type transitions also observed. The gauche-tran conformer has the terminal methyl group out of the plane by nearly $100^{\circ}$. Due to the lack of symmetry in this second conformer, a-, b-, and c- type transitions are observed Many remaining unassigned lines suggests yet another conformer may exist in the 1 K beam. Work is presently underway to study the effect of carrier gas on conformational cooling in this molecule. Also, ab init calculations are being performed to provide insight into the conformational energy differences and barrier heights.