The Microwave Spectrum of Vinylketene

Abstract

We have generated trans-vinylketene by pyrolysis of vinylacetic anhydride and measured and assigned its microwave spectrum. From the derived rotational constants the inertial defect is estimated to be 0.04 uǺ² (700 × kg m²), which indicates a planar molecule. This, together with infrared and mass spectral data, identifies the compound as vinylketene rather than any of its isomers. We have confirmed that vinylketene is also produced by pyrolysis of 1-ethoxybut-3-en- 1-yne, but have found that it is not produced by the pyrolysis of 5-ethylidene-2,2-dimethyl-1,3-dioxan- 4,6-dione.

The dipole moment of vinylketene is 0.97 D (3.24 × 10^-30 C m). An explanation of its lower magnitude as compared with other carbonyl compounds is offered in terms of π-electron delocalization.