Study of Methylidyne Radical (CH and CD) Reaction with 2,5-Dimethylfuran Using Multiplexed Synchrotron Photoionization Mass Spectrometry

At 298 K the reactions of 2,5-dimethlyfuran + CH(X2Π) and + CD radicals were investigated using synchrotron radiation coupled with multiplexed photoionization mass spectrometry at the Lawrence Berkeley National Laboratory. Reaction products were characterized based on their photoionization spectra and kinetic time traces. The CBS-QB3 level of theory was used for all energy calculations, and potential energy surface scans were used to determine thermodynamically favorable reaction mechanisms. The two entrance pathways observed in the reactions are CH insertion within the C-O bond and CH addition to the π-bond system. Both yield initial 6-membered ring radical intermediates. Primary products from the CH addition pathway were observed at m/ z = 108, 66, and 42. The two C7H8O isomers at m/ z = 108 formed are 1,2,4-heptatrien-6-one and 3-hepten-5-yne-2-one. At m/ z = 66, the three C5H6 isomers observed are 1,3-cyclopentadiene, 3-penten-1-yne (E), and 1-pent-4-yne. Ketene ( m/ z = 42) is also observed. From CH insertion entrance channel, the three C6H8 isomers produced are 1,2,4-hexatriene (Z), 2-hexen-4-yne (E), and 1,3,4-hexatriene. Patterns of H-loss, CHO-loss, and CO-loss observed were also in agreement with trends observed in other similar studies. H-assisted isomerization pathways have been considered as well for the formation of m/ z = 66, 80, and 108 isomers.