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Title:Structure and Reactivity of Aryl Carbenes and Aryl Nitrenes: Experimental and Computational Approaches
Author(s):Li, Yu Zhuo
Doctoral Committee Chair(s):Schuster, Gary B.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Organic
Abstract:Part one. Three isomeric aryl carbenes, 1,8-diaza-9-fluorenylidene (18DFL), 3,6-diaza-9-fluorenylidene (36DFL), and 4,5-diaza-9-fluorenylidene (45DFL) were generated by photolyses of their corresponding diazo compounds. The physical and chemical behaviors of the diazo compounds and carbenes were examined and compared with their parent system, diazofluorene (DAF) and fluorenylidene (FL).
Photolysis of 18DAF and 36DAF with ultraviolet light lead to denitrogenation to the singlet carbenes and isomerization to diazirenes. Irradiation of the three diazo compounds with visible light gives some triplet carbenes directly and no diazirenes. All three diazafluorenylidenes are ground state triplets as is FL. However, singlet 18DFL and 36DFL are much more reactive than singlet FL and 45DFL.
A set of carbenes with aromatic substituents were examined with semi-empirical, MINDO3, MNDO, and AM1 methods. The computational results were compared with the experimental determinations of the structure, energy and reactivity for those cases where these parameters have been determined experimentally. The calculations give values of S-T gap that are approximately linearly related to the experimental estimates.
Part two. A set of para-substituted phenyl azides (4-biphenyl azide, methoxyphenyl azide, methylthiophenyl azide, N,N-dimethylaminophenyl azide, chlorophenyl azide, bromophenyl azide, iodophenyl azide, acetophenyl azide, and 4-azidobenzoic acid, 4-nitrophenyl azide), 3-nitrophenyl azide, pentafluorophenyl azide, 2-napthyl azide and 2-pyrenyl azide were examined using time resolved infared and ultraviolet techniques and conventional product analysis.
These experiments put aryl azides into three categories according to the formation of the intermediate: dehydroazipenes from nitrenes with mild electron withdrawing substituents, azirenes from those of highly conjugated systems, and no intermediates from those with strong electron donating or electron withdrawing substituents. The reactivity of a dehydroazipene towards a nucleophile such as diethylamine is strongly related to electronic property of its substituent. An electron withdrawing group tends to increase the reactivity. The life time of halogen substituted dehydroazipenes were also examined for a heavy atom effect.
Issue Date:1988
Description:188 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
Other Identifier(s):(UMI)AAI8908752
Date Available in IDEALS:2014-12-15
Date Deposited:1988

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