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Photoionization induced intermolecular proton transfer in the CH●●●O hydrogen bonded cyclopentanone dimer in the gas phase
Arup K. Ghosh, Piyali Chatterjee and Tapas Chakraborty
Physical Chemistry DepartmentIndian Association for the Cultivation of Science
Jadavpur, Kolkata 700032, India
69th International Symposium on Molecular SpectroscopyJune19th ,2014
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Photochemistry of cyclopentanone
M. Saltmarsh, R. G. W. Norrish, J. Chem. Soc., 445 (1935).S. W. Benson, G. B. Kistiakowsky, J. Amer. Chem. Soc., 64, 80, (1942).F. E. Blacet, A. Miller, J. Am. Chem. Soc., 79, 4327, (1957).R. Srinivasan, Advan. Photochem., 1,83, (1963).R. Bacerra,H. M. Frey, J. Chem. Soc. Faraday Trans.,, 84, 1941, (1988).
All the process start with the Norrish type I cleavage
O O
●●
+2C2H4 CO
+ CO
hν
hν
M. Baba, H. Shinohara, N. Nishi, Chem. Phys., 83, 221, (1984).C. Kosmidis, J. G. Philis, P. Tzallas, Phys. Chem. Chem. Phys. 1, 2945 (1999)T. I. Solling, E. W. G. Diau, C. Kotting, S. de Feyter A. H. Zewail, Chem. Phys. Chem., 3, 79 (2002).
hν
O
H
O
O
O
+ CH2COhν
O
+ C2H4
O
m/z 56
O
+
n(hν)
+ C2H5
O
m/z 55
+O
n(hν)
++ CO
m/z 56
O
n(hν)
++ HCO
m/z 55
O
n(hν)
3
n(hν)
ionization
Intermolecular proton transfer: A new pathway
The weakly hydrogen bonded cyclopentanone dimer is formed under
supersonic jet conditions.
Protonated Cyclopentanone Neutral radical
(Cyclopentanone - H atom)
CH ∙∙∙O hydrogen-bonded (CP)2
CPH+
1.276
(CP-H)●
1.229+
4
Ionization Scheme:
Lock and King, J. Mol. Spectrosc., 36, 53,1970.
266 nm
30,00035,00040,000cm-1
330.29 nm
O
I.E. = 9.26 eV
Absorption spectrum of Cyclopentanone in the gas phase
3.75eV
S0
I.E. = (9.26 eV)
3 3.49 eV=10.47 eV
Rel
ativ
e En
ergy
(eV
)
355 nm266 nm
0
2
4
6
8
10
12
2 4.66 eV =9.32 eV
S1 (nπ*)
(n→3pz)
Rydberg state
4 2.33 eV =9.32 eV
532 nm
5
C2H2+
C2H3+
m/z20 40 60 80 100 120 140 160
No mass peak due to dimer ion
C2H4+
O
m/z 56
O
+
m/z 84
O
m/z 55
+
C3H3+
CH
2CO
+
OH
m/z 85
+
+
Lock and King, J. Mol. Spectrosc. 1970, 36, 53.
266 nm
30,00035,00040,000cm-1
330.29 nm
266 nm photoionization mass spectrum
S0
I.E. (9.26 eV)
Rel
ativ
e En
ergy
(eV
)
266 nm
0
2
4
6
8
10
12
2 4.66 eV = 9.32 eV
S1 (nπ*)
Rydberg State(n→3pz)
3.75eV
6 m/z
C3H3+
C2H3+
C2H4+
20 40 60 80 100 120 140 160
No mass peak due to dimer ion
CH
2CO
+
Lock and King, J. Mol. Spectrosc. 1970, 36, 53.
266 nm
30,00035,00040,000cm-1
330.29 nm
S0
I.E. (9.26 eV)
3 3.49 eV=10.47 eV
Rel
ativ
e En
ergy
(eV
)
355 nm266 nm
0
2
4
6
8
10
12
2 4.66 eV =9.32 eV
S1 (nπ*)
Rydberg State(n→3pz)
355 nm photoionization mass spectrum
Om/z 55
+
m/z 56
O
+
O
m/z 84
+
+
m/z 67
OH+
++ OH
720 40 60 80 100 120 140 160 180
m/z
CP2+ CP2H+
C2H2+
C3H
3+
C2H3+
CH
2CO
+
C2H
5+
Lock and King, J. Mol. Spectrosc. 1970, 36, 53.
266 nm
30,00035,00040,000cm-1
330.29 nm
532 nm photoionization mass spectrum
S0
I.E. = (9.26 eV)
3 3.49 eV=10.47 eV
Rel
ativ
e En
ergy
(eV
)
355 nm266 nm
0
2
4
6
8
10
12
2 4.66 eV =9.32 eVS1 (nπ*)
(n→3pz)
Rydberg state
4 2.33 eV =9.32 eV
532 nm
O
m/z 84
+
OH
m/z 85
+
O
m/z 55
+
O
+
m/z 56
+
m/z 67
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Intermolecular proton transfer through keto-enol tautomerization
IonicKeto-enol Dimer
n(hν) ionizationproton transfer dissociation
n(hν)
ionization
CH ∙∙∙O hydrogen-bonded (CP)2
CPH+
1.276
(CP-H)●
1.229+
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Intermolecular proton transfer: suggested mechanism
+
1.2341.276
1.418 1.062
0.35 eV
Ionization
1.247
1.380
1.236
0.51 e
V
1.52 e
V
1.22 eV
TS (Ionic)Products
IonicDiketo Dimer
IonicKeto-enol
Dimer
9.32 eV ( 2 x 266 nm)
2.712
2.713
1.213
1.213
2.478
2.478
1.210
1.210Neutral
Diketo Dimer
1.263
1.282
2.035
1.023
TS (neutral)
1.10 eV
1.2141.356
1.855 0.977 NeutralKetoenol Dimer
0.61 eV
DFT/B3LYP/6-311++G(d,p)
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Summary:
•Intermolecular proton transfer takes place in the cyclopentanone dimer upon
photoionization.
•The intermolecular proton transfer in the cyclopentanone dimer is dependent on the
wavelength of the laser light.
• We suggest that the intermolecular proton transfer proceeds via a keto–enol
tautomerization mechanism in the ionic state .
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Acknowledgements:
Council of Scientific and Industrial Research (CSIR), India
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