Hydroxy-, derivatives ionization potentials

The ionization potentials, using mass spectrometry, for both 2-hydroxy-and 3-hydroxythiophenes have been compared with data for compounds derived from either tautomeric form in order to analyze the tautomeric composition.124 125 In the 2-hydroxy-substituted system the enol isomer could not be detected. Of the two possible unsaturated lactones the oc,/l-unsaturated form was the major isomer. In the 3-hydroxy-substituted case both the oxo form and the enol form are important. The position of the equilibrium was compared with those of the corresponding furan and sele-nophene systems for both isomers. 

As expected, the ratio of ionic to radical products is also dependent on the ionization potential of the alkyl radical R. For example, in contrast with 1-iodonorbornane (8a), the 3-hydroxy derivative 14 afforded more of the reduction product 15 than ionic product 16 in CHjOH. " Apparently the electron-withdrawing OH group impedes electron transfer. It has been proposed that the ionization potential of R must be 200 kcal/mol for electron transfer to occur. ... 

Studies on the tautomerism of pyridazines with potential tautomeric groups have continued. On the basis of recorded ionization constants and UV spectra of 3,4,5-trimercaptopyridazine and its derivatives, it is concluded that the compound exists as 3,4-dimercaptopyridazine-5(2f/)-thione. Tautomerism of hydroxy- and mercaptopyridazines was investigated with the aid of the corresponding anhydro bases as reference compounds. They exist predominantly in the -one or -thione forms. Similarly, the 3-mercapto-pyridazine-6(l/f)-thione structure in aqueous solution has been redeter-... 

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