cis-2-Propyl-4-t-butylcyclohexanone undergoes cleavage to 4-t-butylcyclohexanone on photolysis. The trans isomer does not undergo fragmentation directly, but is converted to the cis isomer, which then...

cis-2-Propyl-4-t-butylcyclohexanone undergoes cleavage to 4-t-butylcyclohexanone on photolysis. The trans isomer does not undergo fragmentation directly, but is converted to the cis isomer, which then fragments. The trans →cis isomerization is quenched by 1,3-pentadiene, but the photofragmentation is not. Offer an explanation of this pronounced stereochemical effect.