Microwave Spectrum, Barrier to Internal Rotation, and Dipole Moment of cis-3-Pentene-1-yne

The microwave spectrum of cis-3-pentene-1-yne has been observed in the region 8–38 gHz. The barrier to internal rotation of the methyl group was found to be 1140 cal/mole from splittings of the rotational transitions. The rotational constants are A=11790.60 MHz, B=3388.17 MHz, C=2672.20 MHz. The total dipole moment is 0.78D.