Photochemical ( 1,3 ) shifts should proceed through suprafacial shifts ; however , most are non-concerted because they proceed through a triplet state ( i.e. , have a diradical mechanism , to which the Woodward-Hoffmann rules do not apply ) .
Photochemical ( 1,3 ) shifts should be suprafacial shifts ; however , most are non-concerted because they proceed through a triplet state ( that is , they have a diradical mechanism , to which the Woodward-Hoffmann rules do not apply ) .