Vibrational Spectra and Assignments for 1-Fluoro- and 1-Chlorocyclobutenes. Revised Assignment for Cyclobutene

Article abstract of DOI:10.1021/j100162a023

Gas-phase infrared spectra and liquid-phase Raman spectra are presented for 1-chlorocyclobutene and 1-fluorocyclobutene.Complete assignments of vibrational fundamentals are proposed for these molecules of C_s symmetry.For 1-chlorocyclobutene (cm^-1): (a') 3090, 2947, 2940, 1595, 1452, 1434, 1250, 1197, 1165, 1120, 916, 891, 869, 493, 299; (a'') 2980, 2966, 1140, 1070, 1016, 854, 751, 395, 211.For 1-fluorocyclobutene (cm_-1): (a') 3111, 2954, 2948, 1667, 1464, 1437, 1306, 1214, 1189, 1154, 972, 911, 866, 651, 412; (a'') 2982, 2969, 1142, 1076, 1020, 855, 764, 436, 264.Frequencies of CH-rich modes correlate closely for these isotopomer-like molecules.These results along with a Raman spectrum of liquid cyclobutene near -100 deg C have provided evidence for assigning five unsettled vibrational fundamentals of cyclobutene.These modes in cm^-1 are (a₂) ν₉ = 2944, ν₁₁ = 1011, and ν₁₂ = 846 and (b₁) ν₁₉ = 903 and ν₂₀ = 888.Ring-puckering frequencies for a variety of halogen-substituted cyclobutenes are compared and found to follow an understandable pattern.