Broadband Microwave Spectroscopy of Lignin, Biofuels, and Their Pyrolysis Intermediates*

The chemical complexity of the fast-expanding list of potential plant derived biofuels pose a challenge to the scientific community seeking to provide a molecular understanding of their combustion. The direct relationship between molecular structure and rotational frequencies makes rotational spectroscopy highly structure specific; therefore, it is an ideal tool to characterize resonance-stabilized radicals. A high-temperature flash pyrolysis micro-reactor coupled with a supersonic expansion were used to generate the radicals, and a protocol called “strong-field coherence breaking (SFCB)” was used to analyze and speed up the line assignments. The 2-furanyloxy radical, a primary, resonance-stabilized radical formed by loss of a methyl group in the pyrolysis of 2-methoxy furan, was detected and its molecular parameters were determined. Furthermore, the phenoxy radical was investigated and structurally characterized by doing mass-correlated microwave studies. The new structural insights derived from analysis of the observed radicals and the new broadband rotational techniques will be discussed.