Knowledge Bank

Infrared and Raman spectra of 3-chlorocyclopropene and 3-chlorocyclopropene-$d-3$ were recorded under a veriety of sample conditions. From these spectra an essentially complete the frequncies (in $cm-1$) are: $(a\prime )3171,3029,1633,1266,1141,913,713,591,345;(a\prime \prime )3140,1034,1017,866,840,357$. An initial set of internal-coordinate force constants was fitted to the frequences of the $d-0$ and $d-3$ isotopomers. Predictions from these calculations guided the assignments of fundamentals in the spectra of a mixture of the two $d-1$ isotopomers and in the spectra of a mixture of the two $d2$ isotopomers. Frequency assignments for all six isotopomers were used to refine a 20-constant potential function -- a general valence function has 66 constants -- to an average frequency fit of about 10 $cm-1$. In general, interaction constants involving C-Cl motion could not be refined. Large frequency shifts in CH-rich modes in going from the gas phase to condensed phases correlate with hydrogen bonding effects. This behavior of the 3-chlorocyclopropene molecule may be related to the ease with which this molecule loses the chloride ion to form the cyclopropenyl cation.