The Photochemistry of Racemic and Optically Active 2-Iodooctane in Acetonitrile–Water Mixtures

Abstract

Racemic, optically active, and 2-deuterio-2-iodooctane were photolyzed in mixtures of acetonitrile (AN) and water ranging from 95% to 50% AN by volume. The major products in all cases were 1-, ( E)-2-, and ( Z)-2-octene. Minor products consisting of 2-, 3-, and 4-octanol and N-2-, N-3-, and N-4-(methylheptyl)acetamide were also formed in all cases. These products arise from the reaction of octyl cations with water and acetonitrile, with water being 4-5 times more reactive with the cations than acetonitrile. Octane was also formed in small yields, but no meso nor d,l 7, 8-dimethyltetradecane, as was seen in significant amounts in previously reported solvents. The behaviour of the 2-deuterio-2-iodooctane demonstrated that a small fraction of the reaction occurred through the 2-octyl carbene. The carbene was found to react with AN but not with water, an unusual result. Analysis of all these data showed that approximately 90% of the reaction occurred via the 2-octyl cation, 2-4% through the 2-octyl radical, and 4-6% through the 2-octyl carbene. F, the fraction of the intermediates going to product, was determined by examining the behaviour of optically active 2-iodoooctane in 95%, 90%, and 80% AN by volume. F goes up in value as the amount of water in the solvent increases, a result consistent with the photoreaction proceeding largely through ion pairs and free ions.