Application Of Photoelectron-Spectroscopy To Molecular-Properties .43. Photoelectronic Study Of The Flash Vacuum Pyrolysis (Fvp) Of Meldrums Acid-Derivatives - Pe Spectra Of (Alkoxymethylene)Ketenes And ((Alkylthio)Methylene)Ketenes

The (methoxymethylene)ketenes 6 and 7 and the cyclic alkylthio derivative 9, generated by flash-vacuum pyrolysis of the corresponding substituted derivatives of Meldrum's acid, were characterized in the gas phase by photoelectron spectroscopy (PES). The experimental IP's arising from the ejection of an electron from the pi-C=C orbitals were determined and were shown to agree with previous results on parent and (alkylmethylene)ketenes. An interesting feature concerns the observation, for the methylmethoxy compound 7, of different interconverting products at each pyrolysis temperature. The analysis of the PE spectra of these compounds supports Wentrup's mechanism: at 733 K a (carboxyvinyl)ketene 21 would be obtained which is converted at higher temperature (843 K) into the desired (methylmethoxymethylene)ketene (7). This latter, on further increase of the temperature (923 K), would give rise to the vinylketene 23.