What is antiperiplanar?

In organic chemistry, the term "antiperiplanar" refers to a specific conformation of two substituents on a molecule, where they are positioned on opposite sides of a plane. This conformation is commonly associated with the E2 elimination reaction, which requires the leaving group and the hydrogen on the beta carbon to be in the antiperiplanar arrangement for efficient elimination to occur.

The antiperiplanar conformation is considered to be the most favorable for the E2 elimination reaction because it allows for the formation of a pi bond between the two carbon atoms involved. This conformation minimizes steric hindrance and maximizes orbital overlap, resulting in a lower energy transition state and a faster reaction rate.

It is important to consider the antiperiplanar relationship between substituents when predicting and understanding the outcome of chemical reactions, particularly those involving elimination reactions in organic chemistry.