Exchange reactions, proton magnetic

Seitz, L. M., and Brown, T. L., Organometallic exchange reactions. I. Lithium-7 and proton nuclear magnetic resonance spectra of methyllithium and ethyllithium in ether, J. Am. Chem. Soc., 88, 2174 (1966). 

Proton magnetic resonance techniques have been used for the measurement of rates of hydrogen-deuterium exchange of pyrazine (in CHsOD-CHsONa at 164.6") (591) for a study of protonation of pyrazine (1472) for analysis of the reaction mixture from quatemization of 2-substituted pyrazines with methyl iodide (666) for elucidation or confirmation of the structures of alkylpyrazines obtained by alkylation of pyrazines with aldehydes and ketones in the presence of a solution of an alkali or alkaline earth metal in liquid ammonia, or a suspension of these metals in other solvents (614) for a study of changes in chemical shifts produced on ionization of 2-methyl and 2-amino derivatives of pyrazine in liquid ammonia (665) for characterization of methoxymethylpyrazines (686) for the determination of the position of the A -oxide function in monosubstituted pyrazine V-oxides and the analysis of V-oxidation reactions (838) for a study of the structure of the cations of fV-oxides of monosubstituted pyrazines (1136) and for the determination of the structure of the products of peroxyacetic and peroxysulfuric acid iV-oxidation of phenyl- and chlorophenylpyrazines (733b). 

Physical Chemical Characterization. Thiamine, its derivatives, and its degradation products have been fully characterized by spectroscopic methods (9,10). The ultraviolet spectmm of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole yUd (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the piC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the patent cation and its major fragmentation ion, the pyrimidinylmethyl cation (16). 

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