Hydrogen-atom migration and Wolff rearrangement in photolysis of chlorohydroquinone to produce p-benzoquinone and 3-hydroxy-2,4-cyclopentadiene-1-ylidenemethanone

Photolysis of chlorohydroquinone in a low-temperature argon matrix was investigated by Fourier transform infrared spectroscopy with an aid of hybrid density-functional-theory (DFT) calculation. The new photoreaction pathways via a ketocarbene intermediate produced by dissociation of hydrogen chloride upon UV irradiation were found, where a five-membered ring ketene and p-benzoquinone were produced from the ketocarbene by Wolff rearrangement and intramolecular hydrogen-atom migration, respectively. The large H/D isotope effect in the branching ratio for the final products, ketene and p-benzoquinone, was found in the analysis of the growth behavior of the infrared bands, implying that the hydrogen-atom migration occurs by tunneling effect.