Isotope enrichment and stereochemistry of the products from the reaction of electronically excited iodine monochloride with cis- and trans-1,2-dibromoethylene

The reaction of electronically excited iodine monochloride with cis- and trans-1,2-dibromoethylene has been studied in detail. Selective excitation of I/sup 37/Cl, using a CW dye laser, gave cis- and trans-1-bromo-2-chloroethylene products containing up to 78.4 and 73.9% /sup 37/Cl, respectively. The quantum yield of the two products together was about 30%. The product stereochemistry for the reaction of ICl* with 1,2-dibromoethylene is similar to that of free Cl atoms, but differs from that of the competing dark reaction with ICl. A mechanism for reaction with ICl* giving preferential retention of geometry is proposed. 1 figure, 5 tables.