UV Photodissociation of cyclic ketones in the gas phase and cold inert gas matrixes Anamika...
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otodissociation of cyclic ketones in the gas phase cold inert gas matrixes Anamika Mukhopadhyay , Moitrayee Mukherjee, Amit K. Samanta and Tapas Chakraborty Physical Chemistry Department Indian Association for the Cultivation of Science Jadavpur, Calcutta 700032, India 65 th OSU Symposium on Molecular Spectroscopy Date: 21 st June IACS MG17
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Transcript of UV Photodissociation of cyclic ketones in the gas phase and cold inert gas matrixes Anamika...
UV Photodissociation of cyclic ketones in the gas phase and cold inert gas matrixes
Anamika Mukhopadhyay, Moitrayee Mukherjee, Amit K. Samanta and Tapas Chakraborty
Physical Chemistry DepartmentIndian Association for the Cultivation of Science
Jadavpur, Calcutta 700032, India
65th OSU Symposium on Molecular SpectroscopyDate: 21stJune
IACS
MG17
Photodissociation of cyclic ketones: Products
exct : 254 nm
exct : 254 nm
O
O
+ CO
Initial step follows Norrish-I reaction
+ CO
2C2H4 + CO
O
O
O
O
exct : 254 nm
?
?
250 300 350 400 450 500
Molecule of interest
1, 2 cyclohexanedione (1,2 CHD): Considered to be responsible for coffee aroma.Active site of the anticancer drug and anti-tumor steroid
O
O O
O H
H
Monoenolic form
1,2 CHD
Wavelength (nm)
Inte
nsity
(ar
b. u
nit)
O
O
3,4 hexanedione
Goal of study: Fragmentation channels in the gas phase
Small chemical substitution
Ring size effect
Comparision with monocarbonyls to explore the role of 2nd carbonyl on gas phase photochemistry
Environment effect, i.e. if the molecule is taken in a rigid environment
UVC Lamp=254nm
channeltron
-5 kV Signal+
-2 kV
eee
Quadrupole mass filter
Axial Ionizer
Continuous Molecular Beam
Turbo pumpDiffusion pump
Sample
pump
Computer
Gauge
Entrance Lens
Exit Lens
Multipass absorption cell
Detector
MIR source
FTIR Spectrometer
Reaction chamber
Experimental Scheme for gas phase study
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Scheme of UV Photodissociation in Matrix Environment
IR beam from an FTIR spectrometer
266 nm light from Nd:YAG laser
KBr window cooled at 7K temp
………..………..….……..………...…….….………...………...…………………………………………………....
O
O
O
O
λexct =254 nm light
O
O
Proposed Channels
λexct =254 nm light + CO
O
Norrish-I
+ C2H4
cyclobutane
O254 nm light
CO +
CO + 2C2H4
CCO
H
H
λexct =254 nm lightCCO
H
H
CCO
C2H5
H+
O
O
λexct =254 nm lightCO
CH3
H
20 40 60 80 100 120
m/z (amu)
84
70
112
8356
O
O
CH2CH2CH2CH2C=O+(84) + CO(28)O
O
CH2CH2CH2C=O+(70) + H2CCO(42)
O
O
2 CH2CH2C=O+(56)
20 40 60 80 100 120
m/z (amu)
8483
70
55
28
42 56
Mass spectrometric experiment
Before UV exposure
After ½ hr UV exposure
KE of electron=11 eV
0 20 40 60 80 100
O
C2H
4
C
C
O
HH
500 1000 1500 2000 2500 3000 3500 4000
500 1000 1500 2000 2500 3000 3500 4000
Wavenumber (cm-1)
A
A
C
B
D
FTIR Spectrum of 1,2 CHD before and after UV irradiation
Before UV exposure
After ½ hr UV exposureB
C D
949
900 950 1000
1650 1700 1750 1800 2600 2700 2800 2900 3000 3100 3200
Ocyclopentanone
C=O C–H
Ocyclopentanone
2000 2050 2100 2150 2200 2250
2151
A B
Wavenumber(cm-1)
Identification of final products after UV exposure by FTIR spectroscopy
2030 2100 2170 2240
1200 1400 1600 1800 2000 2200
1 hr UV exposure
Before UV exposure
266 nm light
Wavenumber (cm-1)
O
O
O
O
+
Methyl ketene
Ethyl ketene
ketene
Photodissociation of 1,2 CHD in the inert Ar matrix environment
21232127
2142 keteneEthyl ketene
2100 2110 2120 2130 2140 2150 2160
O
O
C
H
HH
O
O
H
C
H
HH
Photodissociation of 3-methyl-1,2-CHD: Substituent effect
O
O
C
H
HH
20 40 60 80 100
0 30 60 90 120 150
Mass m/z (amu)
126
84 98
84
984228
Before exposure
After exposure with 254 nm light
Electron kinetic energy=11 eV
O
CH3
+ CO
CO + C2H4
98
+ C2H4
CO
CH3
H
+
56
42
28
O
O
C
H
HH
CCO
H
H
CO
CH3
H
No reactivity in matrix with 266nm light
Photodissociation of 3-methyl-1,2-CPN in the inert N2 matrix environment
O
CH3
O
HO
O
CH3
+
O
O
CH3
266 nm
O
O
CH3
266 nm2100 2120 2140 2160
2116
2121
2136
Wavenumber (cm-1)
Photoreactivity enhanced compared to the six membered diketone
(K)
(MK)
(DMK)
Summary and outlook:
Gas phase photodissociation results ketene, ethylene, carbonmonoxide and cyclopentanone as the major photoproducts of 1,2 CHD by UV exposure of wavelength 254nm
In 7K argon matrix environment, photodissociation channels are drastically altered, and only ketene, methyl and ethyl ketene are produced
An ortho methyl substitution to 1,2 CHD make the molecule resistant to photodissociation. No photodissociation is found in cold Ar-matrix, and in the gas-phase reactivity is much weaker compared to the parent molecule
On the other hand, methyl substituted 1,2-cyclopentanedione show larger photoreactivity both in gas phase and in matrix
Mass spectrometric as well as spectroscopic measurements for identification of the the reaction intermediates of the above mentioned photodissociation reaction are in progress
Thank You
