SN1 reaction of a two-step reaction mechanism. In which the formation of carbocation takes place before the nucleophile approaches the substrate. Generally, secondary and tertiary haloalkanes show SN1 reactions.
The SN2 reaction is a concerted reaction in which the attack of a nucleophile on the substrate and the departure of the leaving group occur simultaneously. Primary haloalkanes usually display such reactions.
![SN1 Reaction vs. SN2 Reaction](https://scienceinfo.com/wp-content/uploads/2022/11/SN1-Reaction-vs.-SN2-Reaction.jpg)
SN1 and SN2 reactions have different reaction mechanisms. They go through the cation formation step or transition state to produce a product with a different configuration. The key differences between SN1 and SN2 reactions are as follow:
S.N. | SN1 Reaction | SN2 Reaction |
1. | It follows first-order kinetics. | It follows second-order kinetics. |
2. | It is a two-step reaction process. | It is a one-step reaction process. |
3. | The rate of reaction depends on the concentration of substrate only. | The rate of reaction depends on the concentration of both substrate and nucleophile. |
4. | The nucleophile can attack from either side, but the product from the backside attack predominates. | The nucleophile attacks from the back exclusively. |
5. | The rearrangement of carbocation occurs. | Rearrangement products are not possible. |
6. | The reactivity order of alkylhalides is CH3X < 10 < 20 < 30 . | The reactivity order of alkylhalides is CH3X > 10 > 20 > 30 . |
7. | An elimination product is formed due to a side reaction. | No side reaction occurs. |
8. | Mainly electronic factors influence the rate of reaction. | Steric factors influence the rate of reaction. |
9. | Partial racemized product is formed. | Complete stereochemical inversion takes place. |
10. | Mild nucleophiles ( e.g., alcohol, water) generally favor SN1 reaction. | Strong nucleophiles ( e.g., alkoxide) generally favor SN2 reactions. |
11. | Solvents of high polarity favor the SN1 reaction. | Solvents of low polarity favor SN2 reaction. |
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References
- March, J. (1992). Advanced organic chemistry: Reactions, mechanisms, and structure. New York: John Wiley & Sons.
- Peter sykes, A Guide Book to Mechanisms in organic chemistry, (6th edition) Pearson.
- https://chemicalnote.com/sn1-and-sn2-reaction-kinetics-mechanism-stereochemistry-and-reactivity/
- https://www.vedantu.com/chemistry/difference-between-sn1-and-sn2
- https://byjus.com/chemistry/difference-between-sn1-and-sn2/
- https://unacademy.com/content/jee/difference-between/sn1-and-sn2/