Holger E. Chen

CIDNP evidence for a solvent effect on primary photochemical steps for propionaldehyde

Abstract Irradiation of a solution of propionaldehyde results in chemically induced dynamic nuclear spin polarization which is exhibited in the NMR spectrum as enhanced absorption and emission lines for several compounds. The relative intensity of these lines as well as the direction of the line due to the carbonyl hydrogen or propionaldehyde depends on the solvent. This solvent effect can be explained in terms of an effect on some of the primary photochemical steps available to propionaldehyde.

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.