The monoethylbenzo(b)thiophenes: syntheses and mass spectra

The six monoethylbenzo(b)thiophenes were synthesized, the products characterized and their structures unambiguously proven. Of the six, the 4-, 5- and 6-ethylbenzo(b)thiophenes were previously unreported. Several other new compounds were also reported. Mass spectra of the monoethylbenzo(b)thiophenes recorded at 70, 20 and 16 e.v. were very similar with the molecular-ion and the B-cleavage product-ion being very prominant. The mass spectra revealed small, but important, per cent of total intensity differences for certain mass numbers which were dependent upon the position of substitution of the ethyl group. A labeling experime/it was suggested to determine the nature and the origin of the m/e 147 and m/e 121 ions in the mass spectra of the monoethylbenzo(b)thiophenes.