Question

What is the difference between ${\mathrm{S}}_{\mathrm{N}}1$ and ${\mathrm{E}}_1$?

Answer 1

${\mathrm{S}}_{\mathrm{N}}1$ reaction:

1. The reaction is non-concerted and unimolecular.
2. The substrate has a tertiary or conjugated carbocation formed as a leaving group.
3. Nucleophile has more anionic or more basic which is more reactive.
4. The polar aprotic solvent is used that has OH groups like Dimethylsulfoxide, Dimethylformamide, etc.
5. For example -

${\mathrm{E}}_1$ reaction:

1. It involves the elimination of atoms or groups of atoms from two adjacent carbon atoms.
2. It does not occur with a primary alkyl halide.
3. For example - When a haloalkane reacts with alcoholic Potassium hydroxide solution, an alkene is formed as the product. This reaction is called dehydrohalogenation.
   A halogen atom and a hydrogen atom from the haloalkane get eliminated in the form of Hydrogen halide.

Difference between ${\mathrm{S}}_{\mathrm{N}}1\mathrm{and}{\mathrm{E}}_1$

Substitution Reaction Unimolecular	Elimination Reaction Unimolecular
It is a nucleophilic substitution reaction.	It is an elimination reaction.
Substitution of a nucleophile or strong base occurs.	Elimination of a functional group occurs.
The reaction happens involving only one central carbon atom.	This reaction comprises two adjacent carbon atoms.
There is no formation of the double bond in this reaction.	A double bond is formed between two carbon atoms in this reaction.
It requires a nucleophile to form a carbocation.	It doesn't need a nucleophile for the formation of the carbocation.