Reactivities and Applications of Carbon and Nitrogrn Centered Triplet Biradicals
Abstract (Summary)We have investigated the photochemical reactivity and applications of the following triplet biradicals:(a) Triplet alkyl nitrenes, their selective formation and reactivity. (b) Selective generation and detection of triplet imine radicals. (c) Applying triplet imine radical mechanism for the rapid and effective photolysis of alcohols. (d) Understanding the formation of photoenols from 1,4-triplet biradicals of benzophenone and acetophenone derivatives and their application to photorelease of alcohols. (e) Generation of persistent carbon centered radicals by thermolysis. We have demonstrated that triplet alkyl nitrenes can be selectively generated in the photolysis of 1-azidoethanophenones I-1b. However, the triplet alkyl nitrenes I-2b, a long-lived intermediate (lifetime ? 2 ms), undergoes secondary photochemical alpha-cleavage to form benzoyl and imine radicals (see Chapter 1). We have shown a simple and elegant way of generating triplet imine radicals from the photolysis of 4-azidobutyrophenone II-1, and from [2-(azidomethyl) phenyl](phenyl) methanone III-1, detect them using transient spectroscopy. We used product studies and density functional theory (DFT) computational methods to establish the reaction mechanism (see Chapters 2 and 3). Employing the imine radical mechanism, we demonstrate the rapid, solvent independent, and efficient photorelease of alcohol from 2-(2’-azidomethylbenzoyl) benzoic acid methyl ester IV-1 (Chapter 4). Our DFT computational studies allowed us to understand why the photorelease of alcohol from certain Methyl 2-(2’-alkylbenzoyl) benzoic acid esters fail (for example, ester V-4) and why others (esters V-1 and V-5) photoreleased alcohols in inert atmosphere. We similar establish the mechanism of photo-oxidation of the benzylic carbon in esters V-4 and V-1 in the presence of molecular oxygen (see Chapters 5a and 5b). We show how intramolecular hydrogen bonding is used to favor the formation of triplet biradicals VI-2bB which intersystem cross to exclusively form the E-enol VI-2cB. Molecular modeling, products study, quantum yield measurements and transient spectroscopy corroborate our mechanism (see Chapter 6). In chapter 7, we discuss how the ionization potential (IP) of carbon centered radicals can be indicative of the radical’s reactivity with oxygen. We computed the IPs of a series of radicals and verify our hypothesis that radicals with IP greater than 7.4 eV are unreactive with oxygen.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2007