Chemically Induced Dynamic Nuclear and Electron Polarizations-CIDNP and CIDEP

Anomalous electron-spin state populations in the Electron Paramagnetic Re sonance (EPR) spectra of radicals formed during radio lysis experiments were observed in 1963 by FESSENDEN and SCHULER [170a]. This phenomenon did not receive much attention at the time. In 1967, BARGON, FISCHER, and JOHNSEN [5] and independently WARD and LAWLER [7,8] reported a similar phenomenon for Nuclear Magnetic Resonance (NMR) spectra taken during radical reactions: emission or enhanced absorption, or both. The earliest attempts to explain this new NMR phenomenon treated these effects in a way similar to that of Dynamic Nuclear Polarization (DNP) or the Overhauser effect. Although the polarization has a completely different origin, DNP gave its name to this effect: Chemically Induced Dynamic Nuclear Polariza tion (CIDNP). [The name Chemically Induced Dynamic Electron Polarization (CIDEP) was introduced later by analogy with CIDNP]. After the initial publica tions, all the new data demonstrated that the first theory could not be correct. In 1969, a new theory was proposed by CLOSS [18] and independently by KAPTEIN and OOSTERHOFF [23] and called the radical-pair theory. This mechanism was proposed to account for the observations of polarization in both NMR and EPR. The radical-pair theory is based on weak interactions in a pair of radicals: the strength of interaction between the electronic states of the radicals depends in particular on the nuclear-spin states.

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Anomalous electron-spin state populations in the Electron Paramagnetic Re­ sonance (EPR) spectra of radicals formed during radio lysis experiments were observed in 1963 by FESSENDEN and SCHULER [170a]. This phenomenon did not receive much attention at the time. In 1967, BARGON, FISCHER, and JOHNSEN [5] and independently WARD and LAWLER [7,8] reported a similar phenomenon for Nuclear Magnetic Resonance (NMR) spectra taken during radical reactions: emission or enhanced absorption, or both. The earliest attempts to explain this new NMR phenomenon treated these effects in a way similar to that of Dynamic Nuclear Polarization (DNP) or the Overhauser effect. Although the polarization has a completely different origin, DNP gave its name to this effect: Chemically Induced Dynamic Nuclear Polariza­ tion (CIDNP). [The name Chemically Induced Dynamic Electron Polarization (CIDEP) was introduced later by analogy with CIDNP]. After the initial publica­ tions, all the new data demonstrated that the first theory could not be correct. In 1969, a new theory was proposed by CLOSS [18] and independently by KAPTEIN and OOSTERHOFF [23] and called the radical-pair theory. This mechanism was proposed to account for the observations of polarization in both NMR and EPR. The radical-pair theory is based on weak interactions in a pair of radicals: the strength of interaction between the electronic states of the radicals depends in particular on the nuclear-spin states.

Contenu
I. Origin of the CIDNP Effect.- I. Introduction.- II. The Phenomenon.- III. First Interpretations of the CIDNP Effect.- IV. The Radical-Pair Theory.- V. Applications of the CIDNP Effect.- VI. Experimental Procedures.- II. The Theory of the CIDNP Effect.- I. Basic Principles.- II. The Radical-Pair Model.- III. Theoretical Calculation of the CIDNP Effect (CKO).- IV. Kinetic Formulation of the Radical-Pair Mechanism.- V. The Influence of the Magnetic Field H0 on the CIDNP Spectra.- VI. Relaxation and other Effects.- III. Applications to the Study of Chemical Reactions and Magnetic Properties.- I. Applications to the Study of Chemical Reactions.- II. Determination of the Magnetic Properties of Radicals and Molecules.- IV. The Chemically Induced Dynamic Electron Polarization (CIDEP Effect).- I. Introduction.- II. Experimental Procedures.- III. Experimental Results.- IV. The Theory of the CIDEP Effect.- Conclusion.- References.- Subject-Index.