MICROWAVE SPECTRUM OF THE TRANS CONFORMER OF $\beta$-METHOXYPROPIONITRILE

Author Institution: Department of Chemistry, Queen's University KingstonThe microwave spectrum of $\beta$-methoxypropiontrile has been investigated in the region 12-40 GHz. The study has revealed the presence of only one rotational isomer, the all-trans form (Cs symmetry). This is in distinct contrast to the results for the homologous compound, methoxy-$acetonitrile,^{1}$ which was found to be predominantly in the gauche conformation (methyl gauche to cyanide substituent). The stability of the title compound is interpreted in terms of an attractive dipole-dipole interaction. From an analysis of the dominant a type R-branch spectrum, the ground state rotational constants are (in MHZ ) $A = 17 800 \pm 50, B = 1425.53 \pm 0.01, C = 1353 .89 \pm 0.01$. Several vibrationally excited states have also been observed and will be $discussed.^{1}$R. Kewley, Can. J. Chem. 52, 509 (1974)