The mass spectrometer-computer system was pur-chased using funds provided to W. G. Meinschein and J. M. Hayes by the National Science Foundation (GB-13206, GU-2003) and the National Aeronautics and Space . The present developments were principally supported by a grant (to J.M.H.) from the National Institute of General Medical Sciences of the National Institutes of Health (GM-18979).

Abstract-Ionization potential measurements of the volatile species from the three isomers of the tautomeric hydroxyl and mercapto pyridines show that these are in the hydroxy and mercapto forms rather than appearing as lactams and betaines. The corresponding N-methyl lactams and S-and 0-methyl ethers were also studied for comparative purposes.IONIZATION potential measurements for pyridinium-3-oxides and related covalent structures1 indicated to us that such measurements could be used in the determination of the composition of the gaseous species from tautomeric molecules. Our investigations have therefore been extended to simple hydroxy and mercaptopyridines and their heteroatom-methyl analogues. The ionization efficiency curves were interpreted by the semilog plot method.2 The following compounds were studied. The recorded IP values are the average values from three determinations, the deviation being f0-02 eV. The pyridinium thioxide (XVIII) is an exception since the recorded IP value is mainly due to the S-methyl derivative (XI) formed after pyrolytic transal kylation.In the methoxy series (VII to IX) the ionization potential drops in steps 0-2 to 0.3 eV from 9.58 to 8.96 eV in going from the 4-to the 2-position. The dipole moments for these molecules in benzene also decrease

these studies was provided by the Department of Education and Science, and the Royal Norwegian Council for Scientific and Industrial Research. GC-MS facilities were financed by the Natural Environment Research Council and the data acquisition system by the Nuffield Foundation. The programs described in this paper would be available from the National Research and Development Corporation,

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