An investigation of the hyperfine structure of the microwave transitions of ethyl cyanide has led to the following values of the nitrogen quadrupole coupling constants: χaa = − 3.309 ± 0.033, χbb = 1.265 ± 0.013, and χcc = 2.044 ± 0.020 MHz. These results indicate the existence of cylindrical symmetry about the CN bond with a quadrupole coupling constant along the bond axis of χCN = − 4.14 ± 0.04 MHz. The coupling constants in ethyl cyanide and several other cyano compounds have been described by an extended Hückel scheme.

The microwave spectrum of trans-propyleneimine has been studied in the ground state and the first excited state of the methyl torsion. Ground-state rotational constants for the normal isotopic species and for the C3H6N—D species are as follows: A = 16 892.59, B = 6533.63, C = 5761.37 and A = 16 082.31, B = 6338.70, C = 5537.81 MHz, respectively. The height of the barrier to internal rotation has been found to be 2608±26 cal/mole by analysis of splittings of ground-state and first excited-state lines. Measurements of the Stark effect have led to a total dipole moment of 1.57 D, and analysis of hyperfine structure has given the quadrupole coupling constants of the 14N nucleus: χaa=0.67±0.02, χbb=2.24±0.02, χcc=−2.91±0.01 MHz. An estimate has been given of the quadrupole coupling constants in the principal axis system of the electric-field-gradient tensor, and the molecular structure has been discussed.