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Proton Coupled Electron Transfer in Small Molecule Systems
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| 자료유형 | 학위논문 |
|---|---|
| 서명/저자사항 | Proton Coupled Electron Transfer in Small Molecule Systems. |
| 개인저자 | Kolmar, Scott Spencer. |
| 단체저자명 | Yale University. Chemistry. |
| 발행사항 | [S.l.]: Yale University., 2019. |
| 발행사항 | Ann Arbor: ProQuest Dissertations & Theses, 2019. |
| 형태사항 | 433 p. |
| 기본자료 저록 | Dissertations Abstracts International 81-03B. Dissertation Abstract International |
| ISBN | 9781088314814 |
| 학위논문주기 | Thesis (Ph.D.)--Yale University, 2019. |
| 일반주기 |
Source: Dissertations Abstracts International, Volume: 81-03, Section: B.
Advisor: Mayer, James M. |
| 이용제한사항 | This item must not be sold to any third party vendors. |
| 요약 | The thermodynamically coupled transfer of chemistry's most basic components, protons (H+) and electrons (e-), is one of chemistry's most fundamental processes. This so called proton coupled-electron transfer (PCET) is found in critical biological energy transfer reactions, such as the production of O2 in the photosynthetic membranes of plants. PCET also forms the basis of many artificial energy conversion reactions, such as those found in solar fuel cells and electrochemical devices. This mechanism also plays a role in many basic synthetic organic chemistry transformations. Finding and characterizing the many manifestations of PCET remains a popular topic in academic chemistry and provides the basic mechanistic understanding which is required to generate hypotheses about how biology performs its basic functions, how to improve energy conversion technology, and how to move the frontiers of synthetic and physical organic chemistry. This work focuses on developing a picture for understanding PCET through the analysis of this mechanism in the reaction of small organic molecules.Chapter 1 investigates the concerted proton-coupled electron transfer (CPET) reactivity of a popular and longstanding reductive reagent often used in synthetic organic chemistry applications, SmI2(H2O)n. The mechanism of enamine reduction by SmI2(H2O)n is examined in detail with a series of mechanistic experiments. The sum of the data indicate the reactions are best described by CPET. Importantly, a thermodynamic analysis of this system rationalizes the reactivity of SmI2(H2O)n by concluding that the O-H bond strength is extremely low, at ~26 kcal mol-1. The results of this project motivated further study of this powerful PCET reagent.Chapter 2 describes the study of the CPET reduction of anthracene derivatives by SmI2(H2O)n. A series of anthracenes are shown to be readily reduced by SmI2(H2O)n to their dihydroanthracene products. In order to delve deeper into the nature of this mechanism, a linear free energy relationship (LFER) was constructed correlating second and third order rate constants against the driving force for PCET. The thermodynamics were determined using density functional theory (DFT) methods by calculating the bond dissociation free energy of the C-H bond formed in the PCET step of reduction. The kinetics were measured using visible spectroscopy, and showed that the reactions are first order in SmI2 and substrate, but have variable rate order in H2O. The resulting LFER shows that the rate constants are remarkably insensitive to the driving force, and these results are analyzed in the context of physical organic chemistry principles.Chapter 3 deals with a rare and well defined example of intramolecular multiple site concerted proton electron transfer (MS-CPET) that occurs at a C-H bond. A previous report demonstrated that intramolecular MS-CPET in a fluorene-benzoate system has a very shallow LFER when the driving force of the reaction is changed by altering the identity and reduction potential of the external oxidant. To extend this study, we synthesized and studied a series of fluorene-benzoates with substituents that alter the pKa of the internal carboxylate base acceptor. A series of kinetic experiments indicate that the rate constant for MS-CPET is significantly more sensitive to changes in the substituent than to changes in the oxidant identity. A series of DFT calculations were carried out to characterize the transition states of these reactions. The sum of the experimental and computational data help to rationalize the differential sensitivity of the rate constants of MS-CPET to electron transfer and proton transfer driving forces.Chapter 4 describes the results of a kinetic analysis of enamine reduction by SmI2(H2O)n. This chapter describes the problems and obstacles associated with a rigorous kinetic examination of this system.Chapter 5 describes some synthetic contributions to the design of an anthracene-phenol-pyridine system which is utilized to study intramolecular MS-CPET. |
| 일반주제명 | Inorganic chemistry. |
| 언어 | 영어 |
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