Microwave spectrum and conformation of vinyl fluoroformate

Abstract

The microwave spectrum of vinyl fluoroformate displays strong R branch a-type transitions from a planar syn-anti conformer with rotational constants, A 0 = 309(1) MHz, B 0 = 2277.113(6) MHz, and C 0 = 1866.873(6) MHz. Five satellites attributed to successively excited states of the O-vinyl (τ 2(COCC)) torsion have been assigned. Their inertial defects are consistent with a vibrational frequency of 63 cm −1 indicating that the internal rotation barrier about the O-vinyl bond is at least 640 cm −1. Two vibrational satellites attributed to the O-fluoroformyl (τ 1(OCOC)) torsion have been assigned. Their inertial defects are consistent with a torsional frequency of 104 cm −1 which is compatible with an internal rotation barrier about the O-fluoroformyl bond of at least 1675 cm −1. An extensive search for rotational transitions of other conformers, particularly the syn-syn conformer was not successful. Based on the spectral signal/noise ratio of the observed transitions it is estimated that all other conformers must be at least 350 cm −1 higher in energy than the syn-syn conformer.