Direct Observation of Tetrahydrofuranyl and Tetrahydropyranyl Peroxy Radicals via Cavity Ring-Down Spectroscopy.

Room-temperature cavity ring-down (CRD) spectra of the à ← X̃ electronic transition of tetrahydrofuranyl peroxy (THFOO•) and tetrahydropyranyl peroxy (THPOO•) radicals were recorded. The peroxy radicals were produced by Cl-initiated oxidation of tetrahydrofuran and tetrahydropyran. Quantum chemical calculations of the lowest-energy conformers of all regioisomers of these two peroxy radicals have been carried out to aid the spectral simulation. Conformational identification and vibrational assignment were achieved by comparing the experimentally obtained spectra to the simulated ones. The absence of α-THPOO• absorption peaks in the CRD spectrum is attributed to ring opening due to its weak Cα'O bond.