Thiocoumarins spectra

Ultraviolet and near ultraviolet spectra of a number of thiocoumarins have been recorded and discussed. Infrared spectra, in particular concerned with carbonyl absorptions, have been frequently collected,and comparisons made with those of thiochromones. All the usual spectra of thiocoumarin itself have been recorded and analyzed as well as the C-NMR spectrum and the fluorescent characteristics. ... 

The spectroscopic distinction between thiocoumarins and thiochromones is best made by observing the low-field 5-proton in the NMR spectrum of the latter and also the characteristic retro-Diels-Alder fragmentation always observed in the mass spectrum of thiochromones. Thiochromones also show distinctive, strong ultraviolet absorptions at 250-270 nm. ... 

Thiocoumarins characteristically lose carbon monoxide from their strong molecular ion in the mass spectrum, thus forming a benzo[Z>]thiophene cation, invariably accompanied by a large metastable peak. Similar observations are recorded for selenocoumarins. ... 

A superposition of these last two effects is observed in the spectrum of 1-thiocoumarin [24], as compared to that of coumarin [25] or 1-quinolone [26] (Scheme 4), although assignment of each band in these spectra becomes more complex. 

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