A leaving group is an atom or molecule that detaches from an organic molecule, which, after detachment, is called the residual or main part. The ability for a leaving to leave is lability. Leaving group affects the intrinsic reactivity, not the nucleophilic discrimination factors.
The lower the pKa of the conjugate acid, the better the leaving group, because then they can easily stabilize the developing negative charge. SN1 reactionss prefer halide ions as leaving groups.
In room-temperate water, the sequence of lability is:
- Weak, unstable, great lability
- NH2-
- CH3O-
- HO-
- CH3COO-
- F
- water
- Cl
- Br
- I
- N3
- SCN
- NO2
- CN
- Strong, stable
- NO3 is also weaker than F.
- NO3 is also weaker than F.
In the non-mechanistic transformations, leaving group is the actual substituent group present in the substrate and product.External links