The matrix infrared spectra of fulvenone (C₅H₄=C=O) and its thermal decomposition products

Abstract

The matrix IR absorbance spectra of fulvenone, a reactive intermediate in the pyrolysis of lignin, and three of its thermal dissociation products were recorded and analysed using a flash pyrolysis microreactor and ab initio calculations. The predicted spectra of fulvenone, penta-1,2-diene-4-yne, penta-1,3-diyne, and n-${\text{C}}_5^{}{\text{H}}_3^{}\cdot$ matched well with the experimentally observed transitions, and are in good agreement with existing literature data. The cyclic ${\text{C}}_5^{}{\text{H}}_4^{}$ isomer, cyclopentadienylidene, could not be conclusively identified, suggesting that fulvenone is the last relatively stable cyclic species in this pyrolytic chain of reactions. The evolution of the IR data with increasing extent of the pyrolysis shows a gradual trend of dissociation of complex organic molecules towards highly unsaturated hydrocarbons. The isomer-specific analysis by IR assignments of these pyrolytic pathways helps pave the way for further study of biomass thermal reactions, towards possible uses of biomass as a renewable source of energy.

GRAPHICAL ABSTRACT

Keywords:

• Spectroscopy
• matrix IR
• microreactor
• biomass pyrolysis
• ab initio

Acknowledgments

We thank J. F. Stanton for advice relevant to this work specifically, for his contributions to the computational methods used herein, and more generally for his admirable pursuit of close coordination between theory and experiment in physical chemistry and spectroscopy. We also thank G. B. Ellison for bringing this problem to our attention, and for sage input on the organic chemistry of pyrolytic processes.

Disclosure statement

No potential conflict of interest was reported by the author(s).