VIBRATIONAL SPECTRA AND ASSIGNMENTS OF THE FUNDAMENTALS OF CIS-3,4-DIFLUORO-CYCLOBUTENE

Abstract

The cis isomer of 3,4-difluorocyclobutene is formed as a minor product in the reaction of gaseous cis-3,4-dichlorocyclobutene with solid ${AgF_{2}}^{1}.$ On a sample of only 0.1 mmol of cis-3,4-difluorocyclobutene gas-phase IR spectra and liquid-phase Raman spectra were recorded. For this molecule of $C_{s}$ symmetry, $\kappa = 0.49$, and the axis of the least moment of inertia, $I_{a}$, is perpendicular to the symmetry plane. Thus, $a^{\prime\prime}$ modes correspond to bands of A-type shape in the gas-phase infrared spectrum, whereas $a^{\prime}$ modes give bands of hybrid B/C shape. The assigned fundamentals are, in $cm^{-1}: (a^{\prime})$ 3102 (ave. of FR doublet), 2878, 1560, 1350, 1234, 1170, 1050, 998, 837, 769, 408 and 243; $(a^{\prime\prime})$ 3078, 2956, 1343, 1307, 1180, 1092, 1057, 954, 923, 588, 466 and 160. Frequencies in italics are liquid-phase observations; others are gas-phase values. Overall, the assignments correlate reasonably well with the assignments for the trans isomer and for cis-3,4-$dichlorocyclobutene.^{1,2}$