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

对吡啶自由基的可转化单体-二聚体体系进行了动力学研究. ESR和NMR谱仪系统配备齐全，可用于检测化学诱导电子和核自旋极化（CIDEP和CIDNP）现象.利用动力学ESR系统测定了各种吡啶基自由基二聚反应的动力学参数。讨论了中间体存在和不存在时的二聚反应机理. CIDEP对吡啶基自由基二聚体光化学裂解的研究表明，自由基通常是通过单重态自由基对前体产生的，因为在瞬态ESR谱中表现出A（吸收）/E（发射）模式.在CIDEP测量中首次观察到溶液中激发能转移过程中的自旋极化守恒，即在三重态敏化剂存在下，1-甲基-4-烷基吡啶基自由基二聚体的光解离过程.这表明二聚体从三重态光解离的可能性。1，1 '-亚乙基双-和1，1'-三亚甲基双-（吡啶基）双自由基在室温下以dl和meso形式的抗磁性环聚物存在。两种形式的光解离产生的双自由基，这可以在77 K检测。时间分辨ESR测量在有机光反应中的应用，在中间体的检测方面取得了令人兴奋的结果。

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.