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.

Contenu

I. Origin of the CIDNP Effect.- I. Introduction.- II. The Phenomenon.- 1. Examples.- 2. Polarized NMR Spectra.- III. First Interpretations of the CIDNP Effect.- 1. Interpretation by Dynamic Nuclear Polarization (DNP).- 2. Criticisms of the DNP Theory.- 3. Other Interpretations.- IV. The Radical-Pair Theory.- 1. Radical-Pair Model.- 2. Parameters of the Radical-Pair Theory.- V. Applications of the CIDNP Effect.- 1. Determination of the Magnetic Properties of Free Radicals and Molecules.- 2. Studies of Radical Reactions.- VI. Experimental Procedures.- 1. Thermal Reactions.- 2. Photochemical Reactions.- 3. Other Nuclei.- II. The Theory of the CIDNP Effect.- I. Basic Principles.- 1. Spin Functions.- 2. Influence of a Magnetic Field on a Particle with a Spiny.- 3. Interactions between Spins in a Molecule or a Radical.- 4. Other Interactions.- 5. NMR Line Intensities.- 6. The Diffusion Theory for Radicals.- II. The Radical-Pair Model.- 1. Concept of the Radical Pair.- 2. Radical-Pair Generation.- 3. The Disappearance of the Radical Pair.- 4. Energy of a Radical Pair in a Magnetic Field.- 5. The Hamiltonian of the Radical Pair.- 6. Spin Evolution of the Radical Pair with Time.- III. Theoretical Calculation of the CIDNP Effect (CKO).- 1. Reaction Probability.- 2. Calculation of Enhancement Factors.- 3. Forms of the Spectrum. Kaptein's Rules.- 4. Example.- IV. Kinetic Formulation of the Radical-Pair Mechanism.- 1. Principle.- 2. Application.- 3. kij? Calculation.- V. The Influence of the Magnetic Field H0 on the CIDNP Spectra.- 1. Introduction.- 2. Extension of the CKO Theory.- 3. The Density-Matrix Formulation (GCKO Theory).- 4. Kaptein's Theory for Low Field.- 5. Glarum's Theory.- VI. Relaxation and other Effects.- 1. Relaxation.- 2. Sample Form.- 3. Isotopic Substitutions.- III. Applications to the Study of Chemical Reactions and Magnetic Properties.- I. Applications to the Study of Chemical Reactions.- 1. Reaction Types Studied by CIDNP.- 2. Thermal or Photochemical Decompositions of Peroxides.- 3. Photochemical Reactions.- 4. Application of CIDNP to Chemical Kinetics.- 5. Rearrangements.- 6. CIDNP of 13C.- 7. CIDNP of 19F.- 8. CIDNP of 31P and 15N.- II. Determination of the Magnetic Properties of Radicals and Molecules.- 1. Sign Determination.- 2. Hyperfine Coupling Constant A.- 3. Spectroscopic Splitting Factor g or ? g.- 4. J Determination (Overlap Integral).- 5. Relaxation Times.- IV. The Chemically Induced Dynamic Electron Polarization (CIDEP Effect).- I. Introduction.- II. Experimental Procedures.- 1. Electron Irradiation.- 2. UV Irradiation.- 3. Other Methods.- III. Experimental Results.- IV. The Theory of the CIDEP Effect.- 1. Kaptein-Adrian Theory.- 2. Glarum-Marshall Model.- 3. Simple Theory for the H Atom.- Conclusion.- References.- Subject-Index.