Chirped-Pulse Fourier Transform Microwave Spectroscopy Coupled with a Flash Pyrolysis Microreactor: Structural Determination of the Reactive Intermediate Cyclopentadienone.
Chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW) is combined with a flash pyrolysis (hyperthermal) microreactor as a novel method to investigate the molecular structure of cyclopentadienone (C5H4═O), a key reactive intermediate in biomass decomposition and aromatic oxidation. Samples of C5H4═O were generated cleanly from the pyrolysis of o-phenylene sulfite and cooled in a supersonic expansion. The (13)C isotopic species were observed in natural abundance in both C5H4═O and in C5D4═O samples, allowing precise measurement of the heavy atom positions in C5H4═O. The eight isotopomers include: C5H4═O, C5D4═O, and the singly (13)C isotopomers with (13)C substitution at the C1, C2, and C3 positions. Microwave spectra were interpreted by CCSD(T) ab initio electronic structure calculations and an re molecular structure for C5H4═O was found. Comparisons of the structure of this "anti-aromatic" molecule are made with those of comparable organic molecules, and it is concluded that the disfavoring of the "anti-aromatic" zwitterionic resonance structure is consistent with a more pronounced C═C/C-C bond alternation.
†Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, United States.
Nathanael M
NM
Kidwell
†Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, United States.
Vanesa
V
Vaquero-Vara
‡National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States.|∥Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States.
Thomas K
TK
Ormond
‡National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States.|∥Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States.
Grant T
GT
Buckingham
†Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, United States.
Di
D
Zhang
†Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, United States.
Deepali N
DN
Mehta-Hurt
¶Institute of Theoretical Chemistry, Department of Chemistry, University of Texas, Austin, Texas 78712, United States.
Laura
L
McCaslin
‡National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States.
Mark R
MR
Nimlos
⊥Center for Combustion and Environmental Research, Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309-0427, United States.
John W
JW
Daily
†Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, United States.
Brian C
BC
Dian
¶Institute of Theoretical Chemistry, Department of Chemistry, University of Texas, Austin, Texas 78712, United States.
John F
JF
Stanton
∥Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States.
G Barney
GB
Ellison
†Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, United States.
Timothy S
TS
Zwier
Chen nozzle; antiaromatic; chirped-pulse Fourier transform microwave spectroscopy; cyclopentadienone; flash pyrolysis microreactor; hyperthermal nozzle; reactive intermediate