The mass spectra of some 3-, 4-, and 5-substituted thiophene-2-carboxylic acids at 70 eV are reported. The majority of isomeric 5-and 3-substituted compounds can be differentiated by mass spectrometry. In 3-methyl-, 3-methoxy, 3-thiomethyl-, 3-methylsulphinyl-, 3-formyl-thiophene-2-carboxylic acids the fragmentation is influenced by an “ortho-effect” which activates the H2O elimination.
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Fisichella et al. (1982) studied this question.
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