| This dissertation contains three parts. They are: "Direct Detection of Aqueous Diazene: Its UV Spectrum and Decay Activation Parameters", "Absolute Rate Constants in the Concerted Reduction of Olefins by Diazene", and "Reduction of Nitric Oxide by Pentaammineruthenium(II) Complexes of Aromatic Nitrogen Heterocycles".; The UV spectrum of aqueous diazene (N{dollar}rmsb2Hsb2{dollar}, aq), an intermediate from the acid-assisted hydrolysis of azodiformate, presented in Chapter 1 is the first reported since its transient existence was suggested by Thiele in 1892. Under stopped-flow conditions, intermediate N{dollar}rmsb2Hsb2{dollar} is observed to be present with an absorption maximum at 355 nm with {dollar}varepsilon{dollar} = 24 {dollar}pm{dollar} 3 M{dollar}sp{lcub}-1{rcub}{dollar} cm{dollar}sp{lcub}-1{rcub}{dollar}. The rate constant for the second-order dismutation of N{dollar}rmsb2Hsb2{dollar} is (2.2 {dollar}pm{dollar} 0.3) {dollar}times{dollar} 10{dollar}sp4{dollar} M{dollar}sp{lcub}-1{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar} at 25{dollar}spcirc{dollar}C and 0.11 M ionic strength. The temperature dependence of this process, over the temperature interval from 283 to 313 K, leads to the activation parameters {dollar}Delta Hsp{lcub}not={rcub}{dollar} = 13.8 {dollar}pm{dollar} 0.6 kJ mol{dollar}sp{lcub}-1{rcub}{dollar} and {dollar}Delta Ssp{lcub}not={rcub}{dollar} = {dollar}-{dollar}116 {dollar}pm{dollar} 2 J K{dollar}sp{lcub}-1{rcub}{dollar} mol{dollar}sp{lcub}-1{rcub}{dollar}. The dismutation displays an overall deuterium kinetic isotope effect of 3.3, as determined by conducting the reaction in a fully deuterated medium.; In Chapter 2, we report the first measurement of absolute rate constants for the reactions of aqueous diazene with fumaric acid in its three states of protonation, as well as for the reaction with the maleate dianion. The reduction reaction competed with the disproportionation of the reductant itself. The rate constants obtained were (1.32 {dollar}pm{dollar} 0.07) {dollar}times{dollar} 10{dollar}sp2{dollar} M{dollar}sp{lcub}-1{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar} for fumaric acid, (2.4 {dollar}pm{dollar} 0.5) {dollar}times{dollar} 10{dollar}sp2{dollar} M{dollar}sp{lcub}-1{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar} for the hydrogen fumarate anion, (8.0 {dollar}pm{dollar} 0.5) {dollar}times{dollar} 10{dollar}sp2{dollar} M{dollar}sp{lcub}-1{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar} for the fumarate dianion, and 94.5 M{dollar}sp{lcub}-1{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar} for the maleate dianion, all at 25{dollar}spcirc{dollar}C.; In Chapter 3, we report the reduction of nitric oxide (NO) by pentaammineruthenium(II) complexes of aromatic nitrogen heterocycles. The reaction was investigated in acidic aqueous solution at 25{dollar}spcirc{dollar}C. The kinetic study was at 4.5 mM ionic strength, and the pH dependent study was at 0.1 M ionic strength. The rate law is - {dollar}{lcub}dlbrack Ru({lcub}rm II{rcub})rbrackover{lcub}rm d{rcub}t{rcub}{dollar} = 2 ({dollar}ksb1 + ksb2{dollar} (H{dollar}sp+{dollar})) (NO) (Ru(II)) with {dollar}ksb1{dollar} = 0.99 M{dollar}sp{lcub}-1{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar} and {dollar}ksb2{dollar} = 53.7 M{dollar}sp{lcub}-2{rcub}{dollar} s{dollar}sp{lcub}-1{rcub}{dollar} for the Ru(II)-py complex. These results are accommodated by a mechanism involving outer-sphere formation of NO{dollar}sp-{dollar}. The Ru(II): NO consumption ratio is 1:1. The product analysis shows the reaction gives a 100% conversion from NO to N{dollar}sb2{dollar}O (nitrous oxide). |
