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

An investigation of the IR and Raman spectra of trans-3,4-difluorocycl obutene 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 t he ring puckering mode at 171 cm-1 fits into an emerging pattern in wh ich this lowest frequency mode in cyclobutenes appears to be largely i ndependent of other skeletal modes and predictably dependent on the na ture, extent and location of halogen substitution. The assignment of t he configuration of trans-3,4-difluorocyclobutene, which is a new subs tance, is based on an analysis of the NMR spectra of this material and its cis isomer.