Document Detail

Proton-transfer reactions between nitroalkanes and hydroxide ion under non-steady-state conditions. Apparent and real kinetic isotope effects.
MedLine Citation:
PMID:  11456756     Owner:  NLM     Status:  PubMed-not-MEDLINE    
The kinetics of the proton-transfer reactions between 1-nitro-1-(4-nitrophenyl)ethane (NNPE(H(D))) and hydroxide ion in water/acetonitrile (50/50 vol %) were studied at temperatures ranging from 289 to 319 K. The equilibrium constants for the reactions are large under these conditions, ensuring that the back reaction is not significant. The extent of reaction/time profiles during the first half-lives are compared with theoretical data for the simple single-step mechanism and a 2-step mechanism involving initial donor/acceptor complex formation followed by unimolecular proton transfer and dissociation of ions. In all cases, the profiles for the reactions of both NNPE(H) and NNPE(D) deviate significantly from those expected for the simple single-step mechanism. Excellent fits of experimental data with theoretical data for the complex mechanism, in the pre-steady-state time period, were observed in all cases. At all base concentrations (0.5 to 5.0 mM) and at all temperatures the apparent kinetic isotope effects (KIE(app)) were observed to increase with increasing extent of reaction. Resolution of the kinetics into microscopic rate constants at 298 K resulted in a real kinetic isotope effect (KIE(real)) for the proton-transfer step equal to 22. Significant proton tunneling was further indicated by the temperature dependence of the rate constants for proton and deuteron transfers: KIE(real) ranging from 17 to 26, E(a)(D) -- E(a)(H) equal 2.8 kcal/mol, and A(D)/A(H) equal to 4.95.
Y Zhao; Y Lu; V D Parker
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of the American Chemical Society     Volume:  123     ISSN:  0002-7863     ISO Abbreviation:  J. Am. Chem. Soc.     Publication Date:  2001 Feb 
Date Detail:
Created Date:  2001-07-17     Completed Date:  2001-10-11     Revised Date:  2003-10-31    
Medline Journal Info:
Nlm Unique ID:  7503056     Medline TA:  J Am Chem Soc     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1579-86     Citation Subset:  -    
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, USA.
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