Geometrical isomers of alkenes are different compounds with different physical, chemical and biological properties. They are often hard to separate by chromatography or distillation, so it is important that chemists have methods for making them as single isomers.
Chemical reactions on E- and Z-isomers usually give the same type of product, though often with different stereochemistry. The two geometrical isomers may also react at very different rates. The reaction of the conjugated E- and Z-enones shown below with alkaline hydrogen peroxide gives in each case an epoxide, but with different stereochemistry and at very different rates. Click the links below to see how peroxide reacts with E- and Z-enone: