The mercury photosensitized decomposition of norcamphor has been found to lead to carbon monoxide, three hydrocarbons of formula C6H10 and a polymer as the major products. The three hydrocarbons have been identified as 1,5-hexadiene, allylcyclopropane and bicyclo[2.1.1]hexane, respectively. The minor products included bicyclo[2.2.0]hexane and nortricyclene. The formation of 1,5-hexadiene and bicyclo[2.1.1]hexane along with CO is analogous to the formation of ethylene cyclobutane and CO in the photolysis of cyclopentanone. The mechanism of the formation of allylcyclopropane was traced by the use of norcamphor deuterated in the α-methylene group. The process probably involves a symmetric intermediate which can rearrange in one of two equivalent ways to give allylcyclopropane. Mercury sensitized decomposition of d-camphor gave carbon monoxide, 1,5,5-trimethylbicyclo[2.1.1]hexane, 5,6-dimethylheptadiene-1,5 and a polymer as products. The bicyclic hydrocarbon was found to be optically active. The mercury sensitized decomposition of ketones derived from bicyclo[2.2.1]heptane may be a useful route to the synthesis of hydrocarbons derived from bicyclo[2.1.1]hexane. © 1961, American Chemical Society. All rights reserved.