Fate of transient isomer of CH2I2: Mechanism and origin of ionic photoproducts formation unveiled by time-resolved x-ray liquidography

Diiodomethane, CH2I2, in a polar solvent undergoes a unique photoinduced reaction whereby I2− and I3− are produced from its photodissociation, unlike for other iodine-containing haloalkanes. While previous studies proposed that homolysis, heterolysis, or solvolysis of iso-CH2I–I, which is a major in...

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Bibliographic Details
Published in:The Journal of chemical physics 2019-06, Vol.150 (22), p.224201-224201
Main Authors: Park, Sungjun, Choi, Jungkweon, Ki, Hosung, Kim, Kyung Hwan, Oang, Key Young, Roh, Heegwang, Kim, Joonghan, Nozawa, Shunsuke, Sato, Tokushi, Adachi, Shin-ichi, Kim, Jeongho, Ihee, Hyotcherl
Format: Article
Language:English
Subjects:
Iodine
Methanol
Organic chemistry
Photochemistry
Photodissociation
Polarity
Solvents
Solvolysis
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Summary:Diiodomethane, CH2I2, in a polar solvent undergoes a unique photoinduced reaction whereby I2− and I3− are produced from its photodissociation, unlike for other iodine-containing haloalkanes. While previous studies proposed that homolysis, heterolysis, or solvolysis of iso-CH2I–I, which is a major intermediate of the photodissociation, can account for the formation of I2− and I3−, there has been no consensus on its mechanism and no clue for the reason why those negative ionic species are not observed in the photodissociation of other iodine-containing chemicals in the same polar solvent, for example, CHI3, C2H4I2, C2F4I2, I3−, and I2. Here, using time-resolved X-ray liquidography, we revisit the photodissociation mechanism of CH2I2 in methanol and determine the structures of all transient species and photoproducts involved in its photodissociation and reveal that I2− and I3− are formed via heterolysis of iso-CH2I–I in the photodissociation of CH2I2 in methanol. In addition, we demonstrate that the high polarity of iso-CH2I–I is responsible for the unique photochemistry of CH2I2.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.5099002