Direct Observation of a Transiently Formed Isomer During Iodoform Photolysis in Solution by Time-Resolved X-ray Liquidography

Chi Woo Ahn; Hosung Ki; Joonghan Kim; Jeongho Kim; Sungjun Park; Yunbeom Lee; Kyung Hwan Kim; Qingyu Kong; Jiwon Moon; Martin Nors Pedersen; Michael Wulff; Hyotcherl Ihee

doi:10.1021/acs.jpclett.7b03125

Direct Observation of a Transiently Formed Isomer During Iodoform Photolysis in Solution by Time-Resolved X-ray Liquidography

J Phys Chem Lett. 2018 Feb 1;9(3):647-653. doi: 10.1021/acs.jpclett.7b03125. Epub 2018 Jan 22.

Authors

Chi Woo Ahn^{1

2}, Hosung Ki², Joonghan Kim³, Jeongho Kim⁴, Sungjun Park^{1

2}, Yunbeom Lee^{1

2}, Kyung Hwan Kim², Qingyu Kong⁵, Jiwon Moon³, Martin Nors Pedersen⁶, Michael Wulff⁶, Hyotcherl Ihee^{1

2}

Affiliations

¹ Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 305-701, Republic of Korea.
² Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS) , Daejeon, 34141, Republic of Korea.
³ Department of Chemistry, The Catholic University of Korea , Bucheon, 14662, Republic of Korea.
⁴ Department of Chemistry and Chemical Engineering, Inha University , 100 Inha-ro, Nam-gu, Incheon, 22212, Republic of Korea.
⁵ Soleil synchrotron , Saint-Aubin, 91192, France.
⁶ European Synchrotron Radiation Facility (ESRF) , 38000 Grenoble Cedex 9, France.

PMID: 29337571
DOI: 10.1021/acs.jpclett.7b03125

Abstract

Photolysis of iodoform (CHI₃) in solution has been extensively studied, but its reaction mechanism remains elusive. In particular, iso-iodoform (iso-CHI₂-I) is formed as a product of the photolysis reaction, but its detailed structure is not known, and whether it is a major intermediate species has been controversial. Here, by using time-resolved X-ray liquidography, we determined the reaction mechanism of CHI₃ photodissociation in cyclohexane as well as the structure of iso-CHI₂-I. Both iso-CHI₂-I and CHI₂ radical were found to be formed within 100 ps with a branching ratio of 40:60. Iodine radicals (I), formed during the course of CHI₃ photolysis, recombine nongeminately with either CHI₂ or I. Based on our structural analysis, the I-I distance and the C-I-I angle of iso-CHI₂-I were determined to be 2.922 ± 0.004 Å and 133.9 ± 0.8°, respectively.