Pyrrole was tritiated by exchange reaction with HTO in the form of C 4 H 4 NT, the latter substance being changed into C 4 H 3 TNH by transfer of tritium from the nitrogen atom to the carbon atom at 80 °C. This tritium transfer reaction was experimentally proved to occur by intermolecular intraction through hydrogen bonding in pyrrole oligomer. Molecular orbital calculation on hydrogen bond formation was performed using a STO-3G and 4-31 basis sets for various models of pyrrole dimer in order to determine its probable configurations and role in the exchange reactions.
Tritium fractionation factors (a) were measured for the system of pyrrole-water and 2,5-dimethylpyrrole (2,5-DMP)-water mixtures in liquid phase. The a values of N-H groups ("nh) were 1.21 (pyrrole) and 1.19 (2,5-DMP) at 25 °C. Those of C-H groups (aCH) were 0.85 (pyrrole) and 0.74 (2,5-DMP). The a^n values depended on the concentration of pyrrole in some organic solvents, showing characteristic features for each solvent. The relation of <*NH against concentration of pyrrole was notably different from that obtained by the previous authors. The results are discussed in relation to hydrogen bonding of the N-H group.
Tritium exchange reaction /Hydrogen isotope effect jHydroxybenzoic acid / UraeilAbstract Hydrogen isotope exchange reactions of aromatic Compounds and uracil are studied in strong acid media. Logarithm of exchange rate \ shows Ho (Hammett's acidity function) dependence. o-, m-or p-hydroxybenzoic acid shows isomer effect for \ and labelled positions. Comparison of exchange rates of hydrogen-tritium among these Compounds reveals the mechanisms which give reasonable explanations for the observed phenomena. The importance of keto-enol tautomerism in reasonant structures is suggested in the case of uracil.Experimental o-hydroxybenzoic acid (purity > 99.5%) was purchased from Junsei Chemical Co., Ltd.; m-hydroxybenzoic acid, p-hydroxybenzoic acid (98%), o-chlorobenzoic acid (> 99%), from Tokyo Chemical Industries Co., Ltd.; and uracil (95%) from Wako Pure Chemical Industries, Ltd.. These chemicals were purified by reciystallization. Tritiated water (0.5 Ci/g) was purchased from the New England Nuclear Co. and was diluted to appropriate concentration levels for the experiments described in the later section.
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