Hanson, James Edward (1990) I. Matrix isolation of 1,1-diazenes. II. Distance, temperature, and dynamic solvent effects on electron transfer reactions. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-06072007-131625
Part I: Investigations of the reactive intermediates known as 1, 1-diazenes or aminonitrenes are reported. These unstable species were generated by UV photolysis of appropriately substituted carbamoyl azides under matrix isolation conditions. Four systems were investigated: three cyclic dialkyl 1,1-diazenes (1,1-tetramethylenediazene 1, 1, 1-trimethylenediazene 2, and 3,4-dehydro-1, 1-tetramethylenediazene 15) and the first diaryl 1,1-diazene, 1,1-diphenyldiazene 22. 1,1-Diazene 1 could be generated by broad band UV photolysis (200-400 nm) of the carbamoyl azide, but 2 and 22 required narrow band photolysis (290-310 nm) and gave poorer yields. 1, 1-Diazene 15 could not be isolated even at 10 K. The chemical and spectroscopic properties of the 1, 1-diazenes were investigated in some detail, and the results were analyzed with regard to the stability of the various 1,1-diazenes and the different reactive pathways available to 1,1-diazenes with different substituents.
Part II: The dependence of intramolecular electron transfer rates for porphyrin-quinone compounds on distance and temperature was studied. It was found that the rates depend exponentially on the edge-to-edge donor acceptor distance Re as
kET = ko exp [-α Re]
with α values of 1.10 to 1.25 in different solvents. The temperature dependence studies revealed that the electron transfer rates are not activated in a classical sense, but instead depend on the dynamic relaxation properties of the solvent. In 2-methyltetrahydrofuran, the rates are nearly independent of temperature at high temperatures (200-300 K), then begin to decrease with decreasing temperature. In toluene, the rates increase with decreasing temperature, while in deuterated toluene the rates initially increase with decreasing temperature, then go through a maximum around 215 K, and finally decrease. Apart from the unusual solvent isotope effect in the toluene and toluene-8 data, this appears to be the first observation of the rate turnover with solvent "friction" predicted by Kramers. The results were analyzed in terms of theoretical predictions of the dependence of electron transfer rates on the longitudinal relaxation time of the solvent τL using the equation
kET = kNA / 1.00 + (α / KNAτL) + γkNAτL
where kNA is a maximum rate and α and γ are fitted parameters. This equation gave reasonable fits to the data for all three solvents.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Thesis Availability:||Restricted to Caltech community only|
|Defense Date:||8 September 1989|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||21 Jun 2007|
|Last Modified:||18 Nov 2014 17:37|
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