The di-ir-methane rearrangement of a series of meta and para substituted arylvinylmethane reactants was investigated with the aim of determining the patterns of reactivity in systems in which initial excitation is localized in the aryl moiety. Thus the photochemistry of 3-methyl-3-phenyl-l-butene, 3-methyl-3-(p-cyanophenyl)-l-butene, 3-methyl-3-(m-cyanophenyl)-l-butene, 3-methyl-3-(p-methoxyphenyl)-l-butene, and 3-methyl-3-(m-methoxyphenyl)-l-butene was studied. The five systems rearranged photochemically to afford corresponding 1,1-dimethyl-2-arylcyclopropanes. The photochemistry of the cyclopropanes was also studied. Each of these opened to the corresponding 1,3-diradical, which then partitioned itself to isomeric l-aryl-3-methylbutenes. The two processes observed were a 1,4-hydrogen transfer in the diradical and a 1,2-hydrogen shift. Di-ir-methane quantum yields were determined. Also, biacetyl studies permitted determination of singlet vs. triplet reactivity. In the di-ir-methane rearrangements it was determined that, on direct irradiation, the parent arylvinylmethane and the (cyanophenyl)vinylmethanes reacted only via the singlet excited states, while the anisyl di-ir-methane reactants utilized both the singlet and the triplet for rearrangement. However, acetone sensitization was successful in generating the (cyanophenyl)vinylmethane triplets which then rearranged successfully. The main impediment to triplet di-ir-methane rearrangement of the cyanoaryl reactants proved to be relatively inefficient intersystem crossing. In the case of the m-methoxyphenyl reactant it was possible to determine the triplet lifetime. Finally, singlet rates of decay and reaction were determined for the di-ir-methane systems. MeO 22, X = p-Br; Y = Br 24a, X = p-Br 8a, X = p-CN 23, X = m-Br; Y = Cl 24b, X = m-Br 8b, X = m-CNmethane reactants 4-5 were prepared as outlined in Scheme I. Also, as the study developed, it was apparent that a number of secondary photoproducts would require structure elucidation. These were independently synthesized as depicted in Scheme II.Exploratory Photochemistry. Direct Irradiation of Di-ir-methane Reactants. Previously5 the photochemistry of 3-methyl-3-phenyl-l-butene (3) has been observed to afford l,l-dimethyl-2-phenylcyclopropane (6) on direct irradiation. In the present study reactants 4a, 4b, 5a, and 5b were observed to undergo a facile reaction under preparative conditions, affording the corresponding arylcyclopropanes 7a, 7b, 8a, and 8b. The reaction is shown in eq 2. It is seen that, in addition to the di-irmethane rearrangement products, a series of aryl substituted butenes was encountered. In the case of p-methoxy and m-methoxy reactants, there were observed the corresponding feri-butyl aryl ethers. The product distribution under preparative conditions is included in eq 2. We note, however, that only the arylcyclopropanes are primary photoproducts (vide infra).Exploratory Photochemistry. Secondary Reactions. Direct irradiation of the arylcyclopropanes led to three types of products with the...