ISSN:
0030-4921
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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: kapp (sec-1) = 820 and 40 (50°C), ΔF323# (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 NH2 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.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1270040613
