The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds

The central topic of this dissertation is to seek the answer to the question: Is the single transition state model appropriate for (1) the proton transfer reactions of nitroalkanes and (2) the aromatic nucleophilic reactions of trinitroarenes? If not, what are the real mechanisms? This objective has...

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Main Author: Li, Zhao
Format: Others
Published: DigitalCommons@USU 2012
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Online Access:https://digitalcommons.usu.edu/etd/1407
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2400&context=etd
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spelling ndltd-UTAHS-oai-digitalcommons.usu.edu-etd-24002019-10-13T05:51:56Z The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds Li, Zhao The central topic of this dissertation is to seek the answer to the question: Is the single transition state model appropriate for (1) the proton transfer reactions of nitroalkanes and (2) the aromatic nucleophilic reactions of trinitroarenes? If not, what are the real mechanisms? This objective has been accomplished by careful kinetic and mechanistic studies which take advantage of modern digital acquisition of absorbance - time data, combined with extensive new data analysis of results from pseudo-first-order kinetic measurements. Several new analysis procedures for pseudo-first-order kinetics that are capable of distinguishing between single-step and multi-step mechanisms have been introduced and intensively confirmed during the application in the kinetic study of the target reactions. The procedures include (1) half-life dependence of apparent rate constant, (2) sequential linear pseudo-first-order correlation, (3) approximate instantaneous rate constant analysis, and (4) time-dependent apparent kinetic isotope effects. Various conventional and nonconventional pseudo-first-order kinetic analyses of the reactions of nitroalkanes in aqueous solutions revealed that the reactions are complex and involve kinetically significant intermediates. The spectral evidence for the formation of reactive intermediates was obtained by carrying out the kinetic experiments at the isosbestic points where changes in reactant and product absorbance cancel. The apparent deuterium kinetic isotope effects studies indicated that the deuterium kinetic isotope effects are not associated with the formation of the intermediates. The observations of anomalous Brønsted exponents previously found for this reaction series could be rationalized well with the complex mechanisms proposed in this work, which indicate that the nitroalkane anomaly does not exist, but arises from an interpretation based upon the incorrect assumption that the reactions follow a simple one-step mechanism. Simulations revealed that the generally accepted competitive mechanism was not appropriate to describe the Meisenheimer complex formation during the reaction of 2,4,6-trinitroanisole with methoxide ion in methanol. This conclusion is supported by the conventional pseudo-first-order kinetic analysis. A reversible consecutive mechanism that accounts for the kinetic behavior has been proposed, which involves an intermediate dianion complex that is formed reversibly from the initial 1,3-σ-complex, and then eliminates methoxide ion to form the 1,1-σ-complex product. 2012-05-01T07:00:00Z text application/pdf https://digitalcommons.usu.edu/etd/1407 https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2400&context=etd Copyright for this work is held by the author. Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user. For more information contact Andrew Wesolek (andrew.wesolek@usu.edu). All Graduate Theses and Dissertations DigitalCommons@USU complex mechanisms kinetics nitroalkane anomaly nitroalkane proton transfer organic reaction mechanisms trinitroarene SNAr Chemistry Organic Chemistry Physical Chemistry
collection NDLTD
format Others
sources NDLTD
topic complex mechanisms
kinetics
nitroalkane anomaly
nitroalkane proton transfer
organic reaction mechanisms
trinitroarene SNAr
Chemistry
Organic Chemistry
Physical Chemistry
spellingShingle complex mechanisms
kinetics
nitroalkane anomaly
nitroalkane proton transfer
organic reaction mechanisms
trinitroarene SNAr
Chemistry
Organic Chemistry
Physical Chemistry
Li, Zhao
The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds
description The central topic of this dissertation is to seek the answer to the question: Is the single transition state model appropriate for (1) the proton transfer reactions of nitroalkanes and (2) the aromatic nucleophilic reactions of trinitroarenes? If not, what are the real mechanisms? This objective has been accomplished by careful kinetic and mechanistic studies which take advantage of modern digital acquisition of absorbance - time data, combined with extensive new data analysis of results from pseudo-first-order kinetic measurements. Several new analysis procedures for pseudo-first-order kinetics that are capable of distinguishing between single-step and multi-step mechanisms have been introduced and intensively confirmed during the application in the kinetic study of the target reactions. The procedures include (1) half-life dependence of apparent rate constant, (2) sequential linear pseudo-first-order correlation, (3) approximate instantaneous rate constant analysis, and (4) time-dependent apparent kinetic isotope effects. Various conventional and nonconventional pseudo-first-order kinetic analyses of the reactions of nitroalkanes in aqueous solutions revealed that the reactions are complex and involve kinetically significant intermediates. The spectral evidence for the formation of reactive intermediates was obtained by carrying out the kinetic experiments at the isosbestic points where changes in reactant and product absorbance cancel. The apparent deuterium kinetic isotope effects studies indicated that the deuterium kinetic isotope effects are not associated with the formation of the intermediates. The observations of anomalous Brønsted exponents previously found for this reaction series could be rationalized well with the complex mechanisms proposed in this work, which indicate that the nitroalkane anomaly does not exist, but arises from an interpretation based upon the incorrect assumption that the reactions follow a simple one-step mechanism. Simulations revealed that the generally accepted competitive mechanism was not appropriate to describe the Meisenheimer complex formation during the reaction of 2,4,6-trinitroanisole with methoxide ion in methanol. This conclusion is supported by the conventional pseudo-first-order kinetic analysis. A reversible consecutive mechanism that accounts for the kinetic behavior has been proposed, which involves an intermediate dianion complex that is formed reversibly from the initial 1,3-σ-complex, and then eliminates methoxide ion to form the 1,1-σ-complex product.
author Li, Zhao
author_facet Li, Zhao
author_sort Li, Zhao
title The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds
title_short The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds
title_full The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds
title_fullStr The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds
title_full_unstemmed The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds
title_sort kinetics and mechanisms of some fundamental organic reactions of nitro compounds
publisher DigitalCommons@USU
publishDate 2012
url https://digitalcommons.usu.edu/etd/1407
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2400&context=etd
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