 Allylic strain

Allylic strain (also known as A1,3 strain, 1,3-allylic strain, or A-strain) in organic chemistry is a type of strain energy resulting from the interaction between a substituent on one end of an olefin with an allylic substituent on the other end.If the substituents (R and R') are large enough in size, they can sterically interfere with each other such that one conformer is greatly favored over the other.