Effect of Pressure on Chemically Induced Dynamic Nuclear Polarization

Article abstract of DOI:10.1021/jo00342a011

Chemically induced dynamic nuclear polarization (CIDNP) has been observed in the thermolysis of acetyl benzoyl peroxide over a pressure range of 0-200 MPa.Analysis of the CIDNP spectra shows that the application of pressure retards the rate of peroxide cleavage and increases the ratio of cage product to escape product but has no effect on the enhancement factors.The spin-lattice relaxation times of the methyl protons in methyl benzoate nad chloromethane have been determined over the same pressure range; both decrease as pressure is applied.The activation volumes for these processes are -13 and -6.4 cm³/mol, respectively.The principal advance gained by means of this study is that the observation of CIDNP under pressure allows a rapid and reasonably accurate evaluation of the activation volume of the initiator decomposition (4 cm³/mol) and of the difference in activation volume for the formation of escape and cage products (8 cm³/mol).