Inter- and intramolecular photochemical processes
involving the addition of a C–C double (or triple) bond (i) to the 1,2-positions of an arene in which case it is called an ortho photocycloaddition
, with formation of a benzocyclobutene (or a benzocyclobutadiene) derivative, (ii) to the 1,3-positions of an arene in which case it is called a meta photocycloaddition
, with formation of tricyclo[3.3.0.02,8
]oct-3-ene (or octa-3,6-dien) derivatives, or (iii) to the 1,4-positions of an arene in which case it is called a para photocycloaddition
, with formation of bicyclo[2,2,2]oct-2-ene (or octa-2,5-dien) derivatives.
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 303 (https://doi.org/10.1351/pac200779030293)