Quantitative chemically induced dynamic nuclear polarization (CIDNP) study of the photolysis of benzaldehyde in solution

Abstract

Qualitative studies of the polarizations in the CIDNP spectra observed from benzaldehyde in a series of solvents are reported and the reaction mechanism which leads to polarized products in hexane solution is established. The time-evolution of two signals which results from isolated protons in single products has been observed in hexane solution under conditions of low overall conversion to products. The results have been analysed using a kinetic model of the reaction and the diffusion description of CIDNP. The quantitative results are entirely consistent with the model, and values of the diffusional correlation time τ_c= 2.6 ± 0.3 × 10^–12 s and the rate constant for hydrogen transfer between the ketyl radical and ground-state benzaldehyde, k₃= 1 × 10⁶ mol^–1 dm³ s^–1, are reported. A feature of the theoretical treatment is the use of intensity ratios to overcome problems of absolute intensities of lines observed in the products of radical reactions.