Microwave Spectrum, Barrier to Internal Rotation, and Quadrupole Coupling Constants of Cis-1-Chloropropylene

Abstract

The microwave spectrum of CH₃CH=CH³⁵Cl and CH₃CH=CH³⁷Cl was studied in the region from 8–35 kMc/sec. The height of the potential barrier hindering the internal rotation of the methyl top is 620 cal/mole; the Cl quadrupole coupling constants are _χaa^35Cl= —19.66 Mc/sec and _χbb^35Cl=31.05. The dipole moments are _μa=1.47 D and _μb=0.72 D. The even greater lowering of the barrier, trans to cis, for the chlorine compounds as compared with the fluorine analogs supports the hypothesis of a nonbonded interaction between the halogen and the methyl hydrogen atoms.