ISSN:
0538-8066
Schlagwort(e):
Chemistry
;
Physical Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
N-Methyl-N-β-hydroxyethyl picramide (PH) forms a 1:1 (PHS2-) and a 1:2 (PHS24-) anionic σ-complex with sulfite ion. In alkaline solution PH is present mainly in the form of its spiro Meisenheimer complex (M-) which also adds sulfite ion to form a complex MS3-. Rate and equilibrium constants for the various reactions which interrelate the five species PH, PHS2-, PHS24-, M-, and MS3- (scheme I) were determined. PHS24- and MS3- can, in principle, exist in the form of two geometric isomers. Despite a careful search by nuclear magnetic resonance and kinetic techniques, no experimental manifestation of this isomerism could be found. Various limiting situations are discussed under which the absence of experimental evidence does or does not exclude the presence of two isomers. Our preferred but unproven interpretation is that in the case of PHS24- one isomer (trans?) is thermodynamically strongly favored over the other, whereas in the case of MS3- both isomers are of similar thermodynamic stability and have also similar rates. This latter feature would make the isomerism kinetically undetectable. Several other features of scheme I make it an instructive example in complex chemical kinetics.
Zusätzliches Material:
6 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/kin.550110404
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