The two-top molecule 3-penten-2-one: Acetyl methyl torsion in ?,?-unsaturated ketones

Using a molecular jet Fourier transform spectrometer, the microwave spectrum of E-3-penten-2-one, also called methyl propenyl ketone, was recorded in range from 2.0 to 26.5 GHz. Two conformers, antiperiplanar (ap) and synperiplanar (sp), could be identified. Complicated splitting patterns arising due internal rotation acetyl groups resolved, all measured rotational transitions were fitted measurement accuracy. The barrier heights group are 434.149(37) cm?1 358.076(26) for ap sp respectively. For group, is 581.903(45) conformer 595.271(71) conformer. By comparing these results those other ketones categorized class system connecting structures molecules, we extended categorization with new ?,?-unsaturated ketones.