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SN1 SN2 E1 E2 Decision (4)

SN1 SN2 E1 E2 Decision (4) - Solvent

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Introduction

In this video, James from Master Organic Chemistry discusses the role of solvents in determining whether a reaction will proceed via SN1, SN2, E1, or E2 mechanisms. The focus is on understanding how different solvents influence these pathways and making informed decisions based on solvent type.

Main Points/Arguments

- Type of substrate: Whether the carbon attached to the leaving group is primary, secondary, or tertiary.

- Type of nucleophile/base: Strong (charged) nucleophiles/bases favor SN2/E2, while weak (neutral) ones favor SN1/E1.

- Polar Protic Solvents:

    - Have hydrogen bonding (e.g., water, methanol).
    - Decrease nucleophilicity by surrounding nucleophiles with solvent molecules.
    - Favor E2 over SN2 due to decreased nucleophilicity.

- Polar Aprotic Solvents:

    - No hydrogen bonding, but have dipoles (e.g., DMSO, DMF, acetone, acetonitrile).
    - Do not decrease nucleophilicity, allowing nucleophiles to remain "free."
    - Favor SN2 reactions by enabling nucleophiles to attack electrophiles more effectively.

Examples or Evidence

- Solvent: Polar protic (e.g., CH3OH).

- Mechanism: E2 is favored due to decreased nucleophilicity.

- Product: Alkene, following Zaitsev's rule.

- Solvent: Polar aprotic.

- Mechanism: SN2 is favored due to unchanged nucleophilicity.

- Product: Substitution product.

- Solvent: Polar aprotic.

- Mechanism: SN2 favored.

- Product: Substitution product via SN2 mechanism.

Conclusion

The type of solvent significantly impacts whether a reaction follows SN1, SN2, E1, or E2 pathways. Polar protic solvents favor E2 reactions by decreasing nucleophilicity, while polar aprotic solvents favor SN2 reactions by allowing nucleophiles to remain free. Understanding these distinctions helps predict and control reaction outcomes in organic chemistry.

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