CIDNP Chemically Induced exchange

Another magnetic technique for the detection of free radicals uses an ordinary nmr instrument. It was discovered144 that if an nmr spectrum is taken during the course of a reaction, certain signals may be enhanced, either in a positive or negative direction others may be reduced. When this type of behavior, called chemically induced dynamic nuclear polarization145 (CIDNP), is found in the nmr spectrum of the product of a reaction, it means that at least a portion of that product was formed via the intermediacy of a free radical.146 For example, the question was raised whether radicals were intermediates in the exchange reaction between ethyl iodide and ethyllithium (2-39) ... 

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