Raman Spectra of Gases. IV. Methylenecyclobutane and Trimethylene Sulfide

Abstract

The low frequency Raman spectra of methylenecyclobutane and trimethylene sulfide in the gaseous state have been recorded. The observed Q branches for the ring puckering vibration have been assigned as Av=2 transitions from a double minimum potential function. The Q branches for trimethylene sulfide agreed with those predicted from far infrared and microwave data and confirm the predicted energy difference for the v=2 to 3 transition. This is the first direct observation of the ring puckering vibration for methylenecyclobutane. The determined potential function, V = 4.104X 1()5x 4 -1.519X 1()4x 2 , differs from those proposed from the microwave and midinfrared studies but is capable of explaining not only the Raman results but also the previous data. The barrier to inversion was found to be 141±5 cm-1 •

Structure, vibrations and relative stability of 1-methylcyclobutene and methylenecyclobutane tautomers using DFT and CCSD methods

“…Experimentally, it was found using mid-IR spectrum, microwave spectrum and Raman spectrum to be 168 AE 10, 160 AE 40 and 141 AE 5 cm À1 , respectively. 16,27,28 Another fundamental ring puckering is located at $ 658 cm À1 , which is in good agreement with the same mode found at 657.2 cm À1 using mid-IR spectrum 16 and con¯rmed by Raman spectrum. 28 The C¼C stretching theoretically located at $ 1770 cm À1 is experimentally observed at 1675 cm À1 (note that the authors did not assign which mode is which).…”

“…16,27,28 Another fundamental ring puckering is located at $ 658 cm À1 , which is in good agreement with the same mode found at 657.2 cm À1 using mid-IR spectrum 16 and con¯rmed by Raman spectrum. 28 The C¼C stretching theoretically located at $ 1770 cm À1 is experimentally observed at 1675 cm À1 (note that the authors did not assign which mode is which). 29 The same C¼C stretching mode can be compared with the C¼C stretching mode of 2-methylpropene observed at 1661 cm À1 .…”

Ring puckering Raman transitions of trimethylene sulfide and several deuterated analogs

“…same reasoning as for trimethylene oxide [5] and expect that the Av = 2 transitions (v the puckering quantum number) should appear most prominently in the Raman spectra. In fact this has been observed for normal TMS [2], and it is not surprising to find it also for the deuterated compounds. The line positions are given in the spectra shown in Figures 1 to 5.…”

“…Indeed, the Raman observable transitions resulting from the ring puckering of the parent compound, i.e. normal TMS, have been reported already by Durig and his group in 1972 [2]. Since only two-quantum transitions are seen in the Raman spectra one could hope that the missing values for the deuterated materials could be determined in this fashion.…”

Nematic phase nuclear magnetic resonance studies of the molecular structures of cyclobutanone and methylenecyclobutane

“…However, Durig et al (7) have examined the Raman spectrum and derived a potential function which also explained the microwave data (4) and infrared combination bands (8).…”