Question

Are strong bases, such as OH −, NH 2 −, and RO −, poor or good leaving groups?

Answer 1

Consider that strong bases are strong nucleophiles, and thus unstable with the negative charge associated with dissociation from the molecule.

Hence, strong bases are generally very poor leaving groups, but can be converted into good leaving groups that are more stable with the associated negative charge.

A common substituent that's often converted is an alcohol, with reagents like `TsCl, SOCl_2`, and `PBr_3`.