Halon-1211 (CF2ClBr\text{CF}_2\text{ClBr}CF2ClBr) is a bromochlorodifluoromethane compound historically used in aviation fire suppression systems. Like CFCs, when it reaches the stratosphere, it absorbs ultraviolet radiation and undergoes homolytic fission, initiating the catalytic destruction of ozone.
Which initiation step occurs preferentially when CF2ClBr\text{CF}_2\text{ClBr}CF2ClBr absorbs ultraviolet radiation?
CF2ClBr→∙Br+∙CF2Cl\text{CF}_2\text{ClBr} \rightarrow \bullet\text{Br} + \bullet\text{CF}_2\text{Cl}CF2ClBr→∙Br+∙CF2Cl
CF2ClBr→∙Cl+∙CF2Br\text{CF}_2\text{ClBr} \rightarrow \bullet\text{Cl} + \bullet\text{CF}_2\text{Br}CF2ClBr→∙Cl+∙CF2Br
CF2ClBr→∙F+∙CFClBr\text{CF}_2\text{ClBr} \rightarrow \bullet\text{F} + \bullet\text{CFClBr}CF2ClBr→∙F+∙CFClBr
CF2ClBr→∙ClBr+∙CF2\text{CF}_2\text{ClBr} \rightarrow \bullet\text{ClBr} + \bullet\text{CF}_2CF2ClBr→∙ClBr+∙CF2
