Study of Chemically Induced Dynamic Nuclear Polarization of Aliphatic Aldehydes in D2O and other Solvents

The chemically induced dynamic nuclear polarization arising from irradiation of aliphatic aldehydes in D2O and various other solvents is reported. The aldehydes included acetaldehyde, propionaldehyde, isobutyraldehyde, and pivalaldehyde, and the solvents were benzene, acetonitrile, cyclohexane, methylcyclohexane, perfluoromethylcyclohexane, D2O, and D2O/acetonitrile. For propionaldehyde, the variation of c.i.d.n.p. with solvent can be explained by a variation of the relative importance of α-cleavage vs. hydrogen abstraction which occur via an excited triplet state. In addition, when D2O is the solvent, the c.i.d.n.p. provides information about secondary radical reactions not observed in the other solvents. For the other aldehydes, the nature of the solvent does not seem to affect the relative importance of α-cleavage vs. hydrogen abstraction. Acetaldehyde undergoes hydrogen abstraction whereas isobutyraldehyde and pivalaldehyde undgero α-cleavage via an excited triplet state.