The light induced additions of CF3I and C2F5I to acetylene yield the trans 1: 1 adducts predominantly [CF3CH= CHI (trans: cis= 6.7: 1) and C2F5CH= CHI (trans: cis= 9: 1)]. The addition of i-C3F7I to acetylene gives a 1: 1 adduct consisting of a higher proportion of the cis isomer (trans: cis= 1.78: 1). The i-C3F7I-acetylene adduct can be dehydrohalogenated to produce i-C3F7C≍ CH. Difluorocarbene (from (CH3) 3SnCF3) does not add to the olefinic ...