Conformation-specific spectroscopy of alkyl benzyl radicals: effects of a radical center on the ch stretch infrared spectra of alkyl chains

Abstract

An important step in combustion processes is the abstraction of hydrogen to form alkyl benzyl radicals. In this talk we present the results of double resonance spectroscopy methods to explore the conformation-specific infrared spectroscopy of $\alpha$-methylbenzyl, $\alpha$-ethylbenzyl, and $\alpha$-propylbenzyl radicals. A local mode-Hamiltonian model that includes Fermi resonance interactions will be described. This model enables the assignment of the alkyl CH stretch IR spectra of these molecules. This talk will contrast the alkyl chain results to their closed shell analogues, focusing on the the role of the radical site which leads to two important effects. First the CH-stretch frequencies of the $\beta$-carbons are shifted by approximately 50 cm$^{-1}$. Second, internal torsion about the C-C bond between the $\alpha$-C and $\beta$-C atoms modulates these frequency shifts, this producing torsion-vibration mixing. The spectral consequences of this mixing are described.