Photolysis of 2,4-dihydroxy-2,4-dimethylpentan-3-one studied by quantitative time-resolved CIDNP and optical spectroscopy

Abstract

The mechanisms and kinetics of radical reactions induced by pulse photolysis of 2,4-dihydroxy-2,4-dimethylpentane-3-one have been studied by time-resolved chemically induced dynamic nuclear polarization (CIDNP) and optical spectroscopy. The rate constant for the decarbonylation of the 2-hydroxy-2-methylpropanoyl radical is described by A=(8.2 ± 2.0)× 10¹¹ s^–1 and E_a=(23 ± 3) kJ mol^–1 in methanol, and by A=(3.7 ± 1.0)× 10¹¹ s^–1 and E_a=(24 ± 3) kJ mol^–1 in methyl-cyclopentane solvents and leads to a CIDNP memory effect. Rate constants for the self-termination of the 2-hydroxyprop-2-yl radicals are derived from the second-order time dependence of the multiplet nuclear polarization of the product propan-2-ol. The time dependence of its net nuclear polarization is influenced by electron–nuclear cross-relaxation. The ratios of disproportionation to the combination of radical pairs are also obtained.