Millimeter wave free-jet spectrum of vinyl acetate

The rotational spectrum of vinyl acetate has been assigned and measured by millimeter wave absorption free-jet spectroscopy. Only lines of the most stable conformer, the one with the carbonyl oxygen cis with respect to vinyl group and the terminal vinyl carbon trans with respect the acid group, have been observed. The observed species is the most stable one, according to theoretical calculations at the MP2(full)/6-311++G∗∗ level of theory. All rotational lines are split by internal rotation of the methyl group; the value of the barrier for this motion was determined to be V₃ = 1.855(1) kJ mol⁻¹.