Tertiary alkyl halides tend to give a mixture with both inverted and retained configurations at reaction centers. This is because this reaction proceeds through a stable carbocation intermediate and the carbon at the reaction center goes to sp2 hybridized state (planar geometry). The incoming nucleophile can attack from both sides of the plane and can give two products with retained and inverted configuration. If there is a partial interaction with the leaving group (nucleofuge) with carbocation there will be more product with inverted configuration and if there is no interaction with leaving group racemic mixture can be obtained. The rate of the reaction depends on the formation of a carbocation (which is the slow step) and there is one molecule …show more content…
The symbol “A” is used to describe bond making (implies association or attachment) and the symbol “D” is used to describe bond breaking (implies dissociation or detachment). The “+” sign is used to show a stepwise reaction. For example, the SN1 mechanism we describe in figure 2.5 is represented as D + A (implies bond breaking and bond forming happens stepwise). If the reaction is concerted like in the SN2 reaction we describe, represented as AD. This nomenclature has a description about the intermediate also. If the intermediate is stable and can move through the solvent, we use a “+” sign and for unstable intermediate which cannot diffuse through solvent and has a limited lifetime, use “*” sign instead of “+” sign. For example, a secondary alkyl halide undergoes an SN1 type mechanism and has an intermediate with shorter lifetime comparing to corresponding tertiary alkyl halide because stabilization of carbocation by alkyl groups are much lower. Therefore, for secondary alkyl halide has D * A (implying bond breaking or dissociation make unstable intermediate followed by bond forming) and corresponding tertiary alkyl halide has D + A mechanism (implying the same mechanism with stable