Photochemistry of diiodomethane in solution studied by femtosecond and nanosecond laser photolysis. Formation and dark reactions of the CH2I-I isomer photoproduct and its role in cyclopropanation of olefins
Tarnovsky, Alexander LU ; Sundström, Villy LU ; Åkesson, Eva LU
and Pascher, Torbjörn
LU
(2004)
In The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory
108(2).
p.237-249
- Abstract
- Femtosecond and nanosecond photolysis of CH2I2 in acetonitrile at an excitation wavelength of 266-nm yield the ground-state CH2I-I isomer product in similar to70% quantum yield. High isomer formation quantum yields (> 70%) were measured also in n-hexane, dichloromethane, methanol, and ethanol using nanosecond photolysis. The CH2I-I product is formed biphasically within similar to15 ps after excitation and can survive on a nanosecond to microsecond time scale before it decays via a mixture of first- and second-order processes. At 21 degreesC, the first-order rate constants are 1.8 x 10(5) s(-1) in n-hexane, with the measured apparent activation energy of 41 +/- 2 kJ mol(-1) (5-55 degreesC), and 4.3 x 10(6) s(-1) in acetonitrile. These... (More)
- Femtosecond and nanosecond photolysis of CH2I2 in acetonitrile at an excitation wavelength of 266-nm yield the ground-state CH2I-I isomer product in similar to70% quantum yield. High isomer formation quantum yields (> 70%) were measured also in n-hexane, dichloromethane, methanol, and ethanol using nanosecond photolysis. The CH2I-I product is formed biphasically within similar to15 ps after excitation and can survive on a nanosecond to microsecond time scale before it decays via a mixture of first- and second-order processes. At 21 degreesC, the first-order rate constants are 1.8 x 10(5) s(-1) in n-hexane, with the measured apparent activation energy of 41 +/- 2 kJ mol(-1) (5-55 degreesC), and 4.3 x 10(6) s(-1) in acetonitrile. These rate constants correspond to intramolecular decomposition Of CH2I-I into a CH2I. radical and an I atom, with the additional formation of I- in acetonitrile. In methanol and ethanol, the CH2I-I isomer decays faster with the pseudo-first-order rate constants of 2.0 x 10(8) and 1.3 x 10(8) s(-1), respectively, and as in acetonitrile, I-3(-) and I-2(-) ion products dominate the absorption of photolyzed CH2I2 samples at long times. The thermodynamics of the CH2I2 system and its implication for the CH2I-I formation mechanism are discussed. A possible role of the CH2I-I isomer as a methylene transfer agent in photocyclopronation of olefins is investigated. Vibrationally relaxed CH2I-I is demonstrated to react with cyclohexene yielding an I-2 leaving group with the second-order rate constants similar to4.4 x 10(5) M-1 s(-1) in n-hexane, 3.4 x 10(6) M-1 s(-1) in dichloromethane, and 4.2 x 10(6) M-1 s(-1) in acetonitrile. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/139133
- author
- Tarnovsky, Alexander
LU
; Sundström, Villy
LU
; Åkesson, Eva
LU
and Pascher, Torbjörn
LU
- organization
- publishing date
- 2004
- type
- Contribution to journal
- publication status
- published
- subject
- in
- The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory
- volume
- 108
- issue
- 2
- pages
- 237 - 249
- publisher
- The American Chemical Society (ACS)
- external identifiers
-
- wos:000187951600001
- scopus:1642567334
- ISSN
- 1520-5215
- DOI
- 10.1021/jp035406n
- language
- English
- LU publication?
- yes
- additional info
- The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Chemical Physics (S) (011001060)
- id
- e3d59fac-1b0a-4c4e-87ac-90ea5e25df8d (old id 139133)
- date added to LUP
- 2016-04-01 15:59:30
- date last changed
- 2023-04-07 19:31:25
@article{e3d59fac-1b0a-4c4e-87ac-90ea5e25df8d,
abstract = {{Femtosecond and nanosecond photolysis of CH2I2 in acetonitrile at an excitation wavelength of 266-nm yield the ground-state CH2I-I isomer product in similar to70% quantum yield. High isomer formation quantum yields (> 70%) were measured also in n-hexane, dichloromethane, methanol, and ethanol using nanosecond photolysis. The CH2I-I product is formed biphasically within similar to15 ps after excitation and can survive on a nanosecond to microsecond time scale before it decays via a mixture of first- and second-order processes. At 21 degreesC, the first-order rate constants are 1.8 x 10(5) s(-1) in n-hexane, with the measured apparent activation energy of 41 +/- 2 kJ mol(-1) (5-55 degreesC), and 4.3 x 10(6) s(-1) in acetonitrile. These rate constants correspond to intramolecular decomposition Of CH2I-I into a CH2I. radical and an I atom, with the additional formation of I- in acetonitrile. In methanol and ethanol, the CH2I-I isomer decays faster with the pseudo-first-order rate constants of 2.0 x 10(8) and 1.3 x 10(8) s(-1), respectively, and as in acetonitrile, I-3(-) and I-2(-) ion products dominate the absorption of photolyzed CH2I2 samples at long times. The thermodynamics of the CH2I2 system and its implication for the CH2I-I formation mechanism are discussed. A possible role of the CH2I-I isomer as a methylene transfer agent in photocyclopronation of olefins is investigated. Vibrationally relaxed CH2I-I is demonstrated to react with cyclohexene yielding an I-2 leaving group with the second-order rate constants similar to4.4 x 10(5) M-1 s(-1) in n-hexane, 3.4 x 10(6) M-1 s(-1) in dichloromethane, and 4.2 x 10(6) M-1 s(-1) in acetonitrile.}},
author = {{Tarnovsky, Alexander and Sundström, Villy and Åkesson, Eva and Pascher, Torbjörn}},
issn = {{1520-5215}},
language = {{eng}},
number = {{2}},
pages = {{237--249}},
publisher = {{The American Chemical Society (ACS)}},
series = {{The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory}},
title = {{Photochemistry of diiodomethane in solution studied by femtosecond and nanosecond laser photolysis. Formation and dark reactions of the CH2I-I isomer photoproduct and its role in cyclopropanation of olefins}},
url = {{http://dx.doi.org/10.1021/jp035406n}},
doi = {{10.1021/jp035406n}},
volume = {{108}},
year = {{2004}},
}