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

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.