Abstract Twenty-one naphthalenes substituted with alkyl, fluoro, chloro, and cyano groups form photo-adducts with diphenylacetylene (dpa); eight naphthalenes with acyl, ammo, chloro, and bromo substituents do not react. These adducts are derivatives of the adduct (1) as shown primarily by their pmr and mass spectra. Except for 2-t-butylnaphthalene and possibly 1-cyano-naphthalene, two isomeric adducts are formed from naphthalene ...