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- Title
Significant Substituent Effects on Pyridinolysis of Aryl Ethyl Chlorophosphates in Acetonitrile.
- Authors
Adhikary, Keshab Kumar; Hai Whang Lee
- Abstract
The substituent effects on the pyridinolysis (XC5H4N) of Y-aryl ethyl chlorophosphates are investigated in acetonitrile at 35.0°C. The two strong π-acceptor substituents, X = 4-Ac and 4-CN in the X-pyridines, exhibit large positive deviations from the Hammett plots but little positive deviations from the Brönsted plots. The substituent Y effects on the rates are really significant and the Hammett plots for substituent Y variations in the substrates invariably change from biphasic concave downwards via isokinetic at X = H to biphasic concave upwards with a break point at Y = 3-Me as the pyridine becomes less basic. These are interpreted to indicate a mechanistic change at the break point from a stepwise mechanism with a rate-limiting bond formation (ρXY = -6.26) for Y = (4-MeO, 4-Me, 3-Me) to with a rate-limiting leaving group expulsion from the intermediate (ρXY = +5.47) for Y = (4-Me, H, 3-MeO). The exceptionally large magnitudes of ρXY values imply frontside nucleophilic attack transition state.
- Subjects
PYRIDINOLINE; AROMATIC compounds; ACETONITRILE; PYRIDINE; NUCLEOPHILIC reactions
- Publication
Bulletin of the Korean Chemical Society, 2014, Vol 35, Issue 5, p1460
- ISSN
0253-2964
- Publication type
Article
- DOI
10.5012/bkcs.2014.35.5.1460