||Various types of endo and exo monocyclic alkenes, bicyclic alkenes and endocyclic dienes and trienes reactions with iodine were carried out thermally (0-35°C) as well as photolytically (-78°C). Thermal and photochemical iodination of endocyclic alkenes, having no alkyl double bond substituents, provides trans -1,2-diiodo compounds in yields greater than 90%. These vic -diiodides are Isolable and stable under refrigeration, in the dark. However, they undergo conversion to monoiodocycloalkanes upon prolonged standing in room light or temperatures greater than 0°C. Photoiodination of methylenecyclohexane and cyclopentane, as well as cyclohexenes having one or two alkyl substituents at the double bond also provides high yields of vic -diiodides; however, the latter undergo very facile conversion to monoiodocycloalkanes and cycloalkenes at room temperature. Diiodination reactions of certain strained bicycloalkenes and certain monocyclic dienes and triene are included in this dissertation. Reaction of trans -1,2-diiodocyclohexane with methanol and water provides 1,2-iodofunctionalized cyclohexanes in high yields. It has been observed and shown in this dissertation that 1,2-diiodocycloalkanes were facilely formed from the reaction of cycloalkene and elementary iodine without the use of iodine anions and that these diiodides were stable for long periods at room temperature in the dark. These diiodides converted to monolodides simply, by heating under reduced pressure to the boiling point of the starting alkene. It is, therefore, proposed that HI is formed in situ to monoiodocycloalkanes.