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The main article (on 12-Nov-2013) mentions "However, when larger rings are used, double bond isomerization during the reaction becomes a possibility. This energy-wasting process competes with cycloaddition and is evident in reactions that yield mixtures of cis- and trans-fused products." Conjugated linear or cyclic α,β-enones can also become deconjugated to β,γ-enones during photolysis. R-CO-CH=CH-CH2R' → R-CO-CH2-CH=CHR' AdderUser (talk) 21:31, 13 November 2013 (UTC)