<P> Anti addition is in direct contrast to syn addition . In anti addition, two substituents are added to opposite sides (or faces) of a double bond or triple bond, once again resulting in a decrease in bond order and increase in number of substituents . The classical example of this is bromination (any halogenation) of alkenes . </P> <P> Depending on the substrate double bond, addition can have different effects on the molecule . After addition to a straight - chain alkene such as C H, the resulting alkane will rapidly and freely rotate around its single sigma bond under normal conditions (i.e. room temperature). Thus whether substituents are added to the same side (syn) or opposite sides (anti) of a double can usually be ignored due to free rotation . However, if chirality or the specific absolute orientation of the substituents needs to be taken into account, knowing the type of addition is significant . Unlike straight - chain alkenes, cycloalkene syn addition allows stable addition of substituents to the same side of the ring, where they remain together . The cyclic locked ring structure prevents free rotation . </P> <P> Syn elimination and anti elimination are the reverse processes of syn and anti addition . These result in a new double bond, such as in Ei elimination . </P>

What is the difference between syn and anti addition