Photochemistry of Racemic and Resolved 2-Iodooctane. Effect of Solvent Polarity and Viscosity on the Chemistry

The photochemistry of racemic and resolved 2-iodooctane was examined in cyclopentane, methanol, and 2-methyl-2-propanol, media with differing polarities and viscosities. The photochemistry of racemic 2-iodooctane was also examined in the gas phase. The photochemistry of 2-deuterio- and 1,1,1-trideuterio-2-iodooctane in cyclopentane and methanol was also studied. The photoreactions in cyclopentane, 2-methyl-2-propanol, and the gas phase occurred exclusively through homolytic reactions, while in methanol, they occurred predominantly (>53%) through heterolytic reactions. By comparing the disappearance of the optically active substrate with its loss of optical activity, <i>F</i>, the fraction of the initially formed radical pair (RP) or ion pair (IP) resulting in product was determined for the three solvents. Because <i>F</i> contains contributions of both escape of the partners in the RP or IP into the bulk of the solvent and reaction within the RP or IP to yield products other than the substrate, there was no correlation between <i>F</i> and solvent viscosity. The <i>F</i> values will be valuable in assessing the photochemistry of 2-iodooctane in the same media with circularly polarized light.