Vibrationally Resolved Laser-Induced Fluorescence Spectrum of 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 methods 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 \rmG_1'\rmT_2\rmG_3 and \mathrmT_1\mathrmT_2\mathrmG_3 were identified as the spectral carriers. A red shift of the spectrum compared to that of the straight chain alkoxy radical with same number of carbon atoms suggested that the cyclohexyl ring was a slightly better electron donor than the linear alkyl group. Studies also showed that the α and β C cyclohexyl substitutions significantly weakened the β C−C bonds 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 at γ C, the stability of the 3-cyclohexyl-1-propoxy radical became comparable to that of straight chain alkoxy radicals.