Molecular properties of the ”anti-aromatic” species
cyclopentadienone, C5H4=O
Barney Ellison — ISMS, RB05
O
O—
C
C
HC
CH
HC
CH
HC
HC
+
CH
CH
4 π electrons — "anti-aromatic"
Our Essential Collaborators
•Thomas K. Ormond
— Dept. Chemistry (Univ. Colorado)
•John W. Daily
— Mechanical Engineering (Univ. Colorado
•John F. Stanton
•Musahid Ahmed
•Patrick Hemberger
•Timothy S. Zwier
— Institute of Theoretical Chemistry (Univ. Texas)
— LBNL, Advanced Light Source, Beamline 9.0.2
— PSI, Swiss Light Source
— Department of Chemistry, Purdue Univ.
• Transportation
fuels
developed
at
engineering/chemistry interface — “Real fuels” are
complicated
• Engineering models are correspondingly complex —
Mechanisms include 100s of intermediates and 1000s
of reactions. Under-determined.
• We use a hot micro-reactor to study the thermal
cracking of complex fuels.
Goal  identify all decomposition products (atoms,
radicals,
metastables) formed in first 100 µsec.
HC
HC
O
O—
C
C
CH
CH
HC
+
HC
CH
CH
anti-aromatic
Properties of “anti-aromatic” molecule, cyclopentadienone, C5H4=O
1. The re structure of C5H4=O by Chirped Pulsed-FT microwave
spectroscopy
2. Polarized, matrix IR spectrum of C5H4=O
3. Photoelectron Spectroscopy finds IE(C5H4=O)
PEPICO experiments @ Swiss Light Source
4. Rx dynamics of thermal cracking of cyclopentadienone:
C5H4=O (+ M)  CO + HCC-CH=CH2
C5H4=O (+ M)  CO + HCCH + HCCH
The Nature of the Micro-Reactor
Our
experiments
Prof. John Daily (Mechanical Engineering)
“not a Chen nozzle but a tubular reactor”
Micro-reactor  complement to shock tube
1 mm x 3 cm
linguini
1 mm x 3 cm SiC tube @ 300 K — 1700
K resistively heated by @ 10 Amps
CFD modeling — numerical solutions Navier-Stokes
equations
Guan et al., “The Properties of a Micro-Reactor for the Study of the Unimolecular
many lignin monomers
yield C5H4=O
Cyclopentadienone formed in high temperature oxidation
of aromatics
O
HC
HC
H
C
C
H
C
C
O
S= O
O
(+ M)
HC
HC
SO
m/z 48
o-phenylene sulfite
m/z 156
Cyclopentadienone
Preparation
H
C
C
H
C
C
o-quinone
m/z 108
O
O
C
(+ M)
CO
m/z 28
HC
HC
CO
CH
CH
(+ M)
m/z 80
cyclopentadienone
m/z 80
2 HCºCH
m/z 26
CH 2= CH-CºCH
m/z 52
HCCH
Unimolecular Chemistry
Cross-over experiment
50:50
mixture
HCC-CH=CH2
C5H4=O
SO
Chirped-Pulsed Microwave Spectrometer — Brooks Pate/U.
Va.
Purdue: CP FTMW spectrometer
Prof. T. S. Zwier (Purdue)
O
S O
O
(+ M)
HC
HC
SO, CO
H
C
C O
C
H
µtubular reactor/1200 K
8 isotopically substituted cyclopentadienone species
observed by CP-FTMW spectroscopy (Purdue)
12C H =O, 12C D =O
5 4
5 4
C1 13C5H4=O, C2 13C5H4=O, C3 13C5H4=O
C1 13C5D4=O, C2 13C5D4=O, C3 13C5D4=O
Microwave spectra were interpreted by CCSD(T) ab initio
electronic structure calculations (Univ. Texas)
Kidwell, Vaquero-Vara, Ormond, Buckingham, Zhang, Nimlos, Daily, Dian, Stanton, Ellison,
& Zwier, “Chirped-Pulse Fourier Transform Microwave Spectroscopy Coupled with a
Hyperthermal Reactor: Structural Determination of the “Anti-Aromatic” Molecule
Cyclopentdienone,” J. Phys. Chem. Letts. 5, 2201-2207 (2014)
molecule is exactly planar: inertial defect, ∆e = 0
C5H4=O Polarized Infrared Spectrum
Matrix (Ne) isolation of C5H4=O and C5D4=O achieved @ 4 K
Gvib = 9a1  3a2  4b1  8b2
20/24 fundamentals assigned for C5H4=O
17/24 fundamentals assigned for C5D4=O
~1
X A1 C5H4=O
• a1 modes: n1 = 3107, n2 = (3100, 3099), n3 = 1735, n5 = 1333, n7 =
952, n8 = 843 and n9 = 651.
• inferred a2 modes are: n10 = 933, and n11 = 722.
• b1 modes are: n13 = 932, n14 = 822, and n15 = 629.
• b2 fundamentals are: n17 = 3143, n18 = (3078, 3076) n19 = (1601 or
1595), n20 = 1283, n21 = 1138, n22 = 1066, n23 = 738, and n24 = 458.
Ormond, Scheer, Nimlos, Daily, Ellison, and Stanton, “Polarized Infrared
Spectroscopy of Cyclopentadienone, an Important Biomass
Decomposition Product,” J. Phys. Chem. A, 118 708 – 718 (2014).
n3(C5H4=O) 1735 cm-1
experimental spectra
(black)
CCSD(T)/harmonic
adjusted VPT2 (red)
Koenig, Smith, & Snell, J. Am. Chem.
Soc. 99, 6663 (1977)
~
IE(C5H4=O) = 9.49 ± 0.02 eV (X
2A )
2
à 2B2 10.01 eV, nO)
Ionization Energy of cyclopentadienone
Ormond, Hemberger, Troy, Ahmed, Stanton, and Ellison, “The Ionization Energy
of Cyclopentadienone: A Photoelectron-Photoion Coincidence Study,”
Molecular Physics (in press, 2015)
IE(m/z 80) = 9.408 ± 0.018 eV
~+ 2
(0,0)
X A2
-1
+
-1
n6 1020 ± 50 cm
+
+
n4
ms-TPE signal (m/z 80)
1.2
+
n4 1460 ± 50 cm
¯
1.0
+ 2
Ã
B2
n9
660 ± 50 cm
-1
O
C
HC
0.8
CH
+
n9 +
¯ n6
¯
0.6
HC
CH
m/z 80
0.4
0.2
0.0
9.2
9.3
9.4
9.5
9.6
9.7
9.8
photon energy / eV
9.9
10.0
10.1
10.2
Chemistry  How does C5H4=O thermally crack apart?
HC
HC
H
C
C
H
SO
CO
C
C
O
O
S O
O
o-phenylene sulfite
m/z 156
k1
(+ M)
HC
HC
C
HCC-CH= CH 2 + CO
CH
CH
cyclopentadienone
m/z 80
m/z 52
k2
2 HCCH + CO
m/z 26
To measure channels?  Beer’s Law
M + hw  M+ + e
I = Ioe-ns(n)z
Ion current = j+ = (Io – I) = Io(1 - e-ns(n)z) @ ns(n)z Io
or
S26+ = nHCCH sHCCH(E) C F(E)
S52+ = nHCC-CH=CH2F(E’) sHCC-CH=CH2(E’) C F(E’)
Possible to measure n(HCCH), n(HCCH-CH=CH2) with
tunable VUV radiation (synchrotron)
Ormond et al.
“Pyrolysis of
Cyclopentadienone:
Mechanistic Insights
From a Direct
Measurement of
Product Branching
Ratios “
J. Phys. Chem. A
in press, June 2015.
Molecular properties
of C5H4=O now well
known:
• Chirped Pulsed-FT
microwave  re
structure
•Polarized Infrared
Spectra (Ne matrix)
Gvib = 9a1  3a2  4b1 
8b2
20/24 fundamentals
•IE(C5H4=O) = 9.408 ± 0.018 eV
assigned for C5H4=O
•EA(C5H4=O) = 1.06 ± 0.01 eV
Sanov et al. J. Phys. Chem. A
(2014)
• C H =O  CO + 2 HCCH or
HCC-CH=CH
measured