VIBRATIONAL-SPECTRA AND ASSIGNMENTS FOR TRANS-3,4-DIFLUOROCYCLOBUTENE

An investigation of the IR and Raman spectra of trans-3,4-difluorocyclobutene has yielded an assignment of all 24 vibrational fundamentals. These frequencies are in cm-1: (a) 3106, 2977, 1559, 1354, 1193, 1175, 1143, 1038, 993, 931, 602, 309, 171; (b) 3088, 2976, 1332, 1298, 1201, 1065, 971, 844, 684, 426, 324. This assignment correlates well with the fundamentals of trans-3,4-dichlorocyclobutene. The frequency for the ring puckering mode at 171 cm-1 fits into an emerging pattern in which this lowest frequency mode in cyclobutenes appears to be largely independent of other skeletal modes and predictably dependent on the nature, extent and location of halogen substitution. The assignment of the configuration of trans-3,4-difluorocyclobutene, which is a new substance, is based on an analysis of the NMR spectra of this material and its cis isomer.