The Rotational Spectrum of 2-Furanyloxy Radical.

We report the hyperfine-resolved rotational spectrum of gas-phase 2-furanyloxy radical (•O-C4H3O) in the 6-36 GHz frequency range recorded using cavity Fourier transform microwave spectroscopy. These observations have yielded a precisely determined set of rotational constants, electron spin-rotation parameters, and proton hyperfine coupling constants. Our results enable a quantitative comparison of the structural and electronic properties of 2-furanyloxy with those of phenoxy and other closely related radicals, providing detailed physical insights into these prototypical resonance-stabilized π systems. The accurate laboratory rest frequencies derived from our measurements enable the quantification of the gas-phase chemistry of 2-furanyloxy in both the laboratory and in space, where the oxidation of aromatic rings remains poorly understood.