Kinetic Studies on the Reaction of Pyridinyl Radicals byMeans of Time-Resolved Magnetic Resonance Spectroscopy

点击翻译按钮获取中文摘要

Kinetic studies for the convertible monomer-dimer systems of pyridinyl radicals have been carried out.1. ESR and NMR spectrometer systems were fully equipped for the detection of chemically induced electron and nuclear spin polarization (CIDEP and CIDNP) phenomena.2. Kinetic parameters for the dimerization of various pyridinyl radicals were determined by the use of a kinetic ESR systems. The dimerization mechanisms with and without intervension of intermediate were discussed.3. The CIDEP studies on the photochemical cleavage of pyridinyl radical dimers elcuidated that the radicals are generally produced through the singlet radical pair precursor, since an A(absorption)/E(emission) pattern was exhibited in the transient ESR spectra.4. A spin polarization conservation during excitation energy transfer in solution was firstly observed in the CIDEP measurements for the photodissociation of the 1-methyl-4-alkylpyridinyl radical dimers in the presence of triplet sensitizers. This suggests a possibility of the dimer photodissociation from the triplet state.5. The 1,1'-ethylenebis- and 1,1'-trimethylenebis-(pyridinyl) diradicals exist as the diamagnetic cyclomers of dl and meso forms at room temperature. Both forms photodissociate to generate the diradical, which can be detected at 77 K.6. Application of time-resolved ESR measurement to some organic photoreactions led to exciting results in the detection of intermediates.