Give the SN1 mechanism for the formation of 2-ethoxy-3-methylbutane, the unrearrangedproduct in this reaction.
Solution 25P :
Here, we have to give the SN1 mechanism for the formation of 2-ethoxy-3-methylbutane
SN1 mechanism is a substitution reaction involving a nucleophile where 1 specie is involved in the slowest rate determining step. ‘SN’ stands for nucleophilic substitution and ‘1’ determines that the rate determining step is unimolecular. Rate determining step is a step in a multistep reaction, that controls the overall reaction rate.
SN1 mechanism for the formation of 2-ethoxy-3-methylbutane is as follows :
In SN1 mechanism, first, the dissociation of the halogen takes place. In the compound below, Br is the halogen and hence is a leaving group and dissociation of it takes place, producing secondary carbocation as shown below :
Here, the Bromide group, a halogen which is the leaving group, dissociates from the compound 2-ethoxy-3-methylbutane in presence of heat or light, and produces secondary carbocation. The carbocation is secondary carbocation, as the carbon atom bearing positive charge is bonded to 2 carbon atoms.
The dissociation of halogen is the slowest step in the mechanism and in this step there is only 1 specie involved and a nucleophile is involved in the second step and hence it is called as SN1 mechanism.
Step 3 :
The above step describes the nucleophilic attack, which is a second step in the SN1 mechanism.
Here, the ethanol is supplied as nucleophile. A nucleophilic attack takes place from bottom, forming a bond with the carbocation and the substitution of nucleophile takes place producing the product that has OH group and has a positive charge on it.
Because the oxygen atom in the product has a positive charge on it, and there is still availability of ethanol to it, further reaction takes place where a hydrogen atom should be lost, to form a stable compound. This is the step 3 of SN1 mechanism.