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Proton exchange and protonation of substituted oxadiazoles in trifluoroacetic acid

✍ Scribed by Mohindar S. Puar; Allen I. Cohen

Publisher
John Wiley and Sons
Year
1972
Tongue
English
Weight
310 KB
Volume
4
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

The rates of NHCOOH proton exchange between 5‐amino‐(1a) and 5‐N‐methylamino‐(1b)3‐[2‐(5′‐nitro‐2′‐furyl)vinyl]‐1,2,4‐oxadiazoles and trifluoroacetic acid (TFA) have been measured by NMR spectroscopy. The values of the first‐order rate constant and thermodynamic parameters for 1a and 1b, respectively, are: k~app~ (sec^−1^) = 820 and 40 (50°C), ΔF (kcal/mole) = 14·7 and 16·5, ΔH^#^ (kcal/mole) = 17·3 and 24·3 and ΔS^#^ (e.u.) = 17 and 34. The comparison of rate constants indicates that after correction for proton equivalency proton exchange in 1a is faster than in 1b by a factor of ten. The presence of an NH~2~ proton resonance (1a) and an N‐methyl doublet (J = 5·0 Hz) between 0 and 30° (1b) suggests that 1a and 1b are present as amines and not as imines in TFA.

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