P. Granger - Böcker

The idea of this NATO school was born during philosophical discussions with Dr Brevard on the present and future of NMR during a night walk under the palm trees in Biskra during a seminar held in this oasis. It was clear for us that the recent progress in the field of NMR, especially inverse spectroscopy and the development of MAS, was opening new perspectives for chemists. We realised also that organometallic and inorganic chemists were not clearly informed about the potentialities of all the new methods. NA TO, with its summer schools, was offering a good opportunity to propose to the chemical community a session where those problems would be largely developped. This School is then the prolongation of the two previous ones: Palermo in 1976 on "the less receptive nuclei" and Stirling in 1982 on "the multinuclear approach to NMR spectroscopy" . It was divided into two sub-sessions: NMR in the liquid state and NMR in the solid state. This is reflected in the book organization. As indicated by the title of this School, we were mainly concerned with the methodological aspects of multinuclear NMR. If many examples are given, they appear only as a support for the understanding of the theory or in explanation of some practical aspects of the different experiments. Each domain is introduced by a lecture which presents selected examples.

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.