Knowledge Bank

To determine the structure of propiolamide, $HCCCONH2$, and in particular to show whether the molecule is planar in its equilibrium configuration, we have measured the microwave spectra of three isotopic species in the ground vibrational state. In addition, we have obtained the spectra of the normal species in three excited vibrational states. From them we have obtained rotational constants, inertial defects, centrifugal distortion constants and $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}N$ nuclear quadrupole coupling constants. From the general appearance of the spectrum, and from the parameters determined from it, the molecule has been shown indeed to be most probably planar. The potential function for $NH2$ inversion appears to be very similar to that of formamide, namely somewhat anharmonic, but with zero barrier to $planarity1$ With the assumption of planarity the dipole moment has been found to be $3.67\pm 0.02$ Debye, essentially parallel to the CO bond.