Spectroscopic studies of some substituted methyl formates. Part 1.—Microwave spectra and internal rotation barriers of methyl-fluoroformate, -propiolate, -cyanoformate, -acrylate and -acetate

Abstract

The stable molecular conformations of methyl-fluoroformate, -propiolate, -cyanoformate, -acrylate (cis) and -acetate have been shown to be planar, and for the latter four compounds the cis ester molecular skeleton has been established. Barriers to internal rotation of the methyl group were measured from splittings of the microwave lines for each compound. [XCOOCH₃; X = F, V₃= 1077; X = HCC, V₃= 1266; X = CN, V₃= 1172; X = CH₃, V₃= 1215; X = CH₂CH, V₃= 1220 (values of V₃ in cal/mol).] For methyl acetate a value of 307 ± 50 cal/mol for the acetyl methyl group was calculated from internal rotation splittings in the spectrum of CD₃COOCD₃. The dipole moments of methyl-fluoroformate and cyanoformate were 2.83 and 4.23 D respectively.