[CrazyAssasin]

According to Woodward-Hoffmann rules photochemical [1,3] shift is allowed suprafacially and theoretically this reaction is possible to happen just as [1,5] shift does thermally. But for some reason there are no such kind of migration of double bonds across a molecule, and if it was possible I believe for example double bonds of unsaturated fatty acid should become conjugated with carbonyl under intensive exposure to light. So why don't we see any effect of [1,3] shift?

[Irlanur]

you could argue with FMO-theory (or orbital correlation diagrams or state correlation diagrams...)