Nu− C Nu
Antibondin
L C + L−
gorbital
Bonding orbital
2) The nucleophile attacks the carbon bearing the leaving group from the back
side.
i) The orbital that contains the electron pair of the nucleophile begins to
overlap with an empty (antibonding) orbital of the carbon bearing the
leaving group.
ii) The bond between the nucleophile and the carbon atom is forming, and the
bond between the carbon atom and the leaving group is breaking.
iii) The formation of the bond between the nucleophile and the carbon atom
provides most of the energy necessary to break the bond between the carbon
atom and the leaving group.
- Walden inversion:
- The configuration of the carbon atom becomes inverted during SN 2 reaction.
- The first observation of such an inversion was made by the Latvian chemist Paul
Walden in 1896.
- Transition state:
- The transition state is a fleeting arrangement of the atoms in which the
nucleophile and the leaving group are both bonded to the carbon atom
undergoing attack.
- Because the transition state involves both the nucleophile and the substrate, it
accounts for the observed second-order reaction rate.
- Because bond formation and bond breaking occur simultaneously in a single
transition state, the SN2 reaction is a concerted reaction.
- Transition state lasts only as long as the time required for one molecular
vibration, about 10–12 s.
