| Chapter 1. Tetramethylphenylenediamine (TMPD) undergoes a one electron transfer to ('1)O(,2) in H(,2)O; the formation of TMPD('+) (Wurster's blue) is detected by laser flash spectroscopy. The formation of TMPD('+) is competitively quenched by known ('1)O(,2) quenchers. Furthermore, there is a large increase in TMPD('+) formation in D(,2)O, relative to H(,2)O, as would be anticipated for a ('1)O(,2) reaction. The rate (k(,r)) of electron transfer to ('1)O(,2) is shown to be (3.3 (+OR-) 1.5) x 10M('9)M('-1)s('-1), close to the diffusion-controlled limit. The formation of observable ions does not take place in any solvent other than H(,2)O(D(,2)O), or with any other of the electron rich aromatic amines studied. It is suggested that the formation of observable radical ions depends on the ease of ionization of the substrate and on the solvation of the resulting ions.; Chapter 2. The interaction of a variety of substrates with the singlet excited states of 9-cyanoanthracene, ('1)CNA, and 9,10-dicyanoanthracene, ('1)DCA, leads to enhanced intersystem crossing, as demonstrated by transient triplet-triplet absorption spectra. The (T-T) spectra showed maximum absorptions at 427nm and 440nm for ('3)CNA and ('3)DCA respectively. The relative amount of intersystem crossing, determined by the intensity of the transient, is substrate dependent. The enhanced intersystem crossing leads to increased formation of ('1)O(,2) and is a major source of ('1)O(,2) in many cyanoaromatic sensitized oxidations.; Chapter 3. The interaction of singlet oxygen with the olefin 2,5-dimethyl-2,4-hexadiene (DMHD) leads to both reaction and quenching. Although the initial interaction with singlet oxygen is nearly independent of solvent, the relative amount of quenching depends on solvent. The singlet oxygen oxidations of 2-methyl-2-pentene (2M2P) and DMHD are studied in detail. Both solvent and temperature effects are examined. It is concluded that the initial interaction between 2M2P and ('1)O(,2) (which gives only ene products) and the initial interaction between DMHD and ('1)O(,2) (which gives ene products, dioxetane and nonreactive quenching) are identical. It is also suggested that the quenching path for DMHD involves formation of an intermediate 1,4-biradical, which undergoes intersystem crossing and decays to ground state oxygen and DMHD. |
