Vibrationally Resolved Laser-Induced Fluorescence Spectrum of the 3-Cyclohexyl-1-Propoxy Radical

Alkoxy radicals bearing cyclic substituents are oxidation intermediates of important hydrocarbon compounds in atmospheric chemistry and pharmacology. Spectroscopic study can provide diagnostic method for monitoring these radicals in reactions and investigating their structure-reactivity effect. In this work, vibrationally resolved laser-induced fluorescence (LIF) spectrum of the 3-cyclohexyl-1-propoxy radical was obtained in supersonic jet condition. Low energy conformers G₁' T₂ G₃ and T₁ T₂ G₃ were identified as the spectral carriers. A red shift of the spectrum compared to the straight chain alkoxy radical with same carbon atoms suggested that the cyclohexyl ring was a slightly better electron donator than the linear alkyl group. Studies also showed that the α and β C cyclohexyl substitution significantly weakened the βC-C bond of the radicals, and conversely, the strength of the C-C bonds on cyclohexyl ring decreased as its distance from the O radical decreased. When cyclohexyl substitution occurred on γ C, the stability of the 3-cyclohexyl-1-propoxy radical became comparable to that of straight chain alkoxy radicals.