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Questions and Answers
What is a characteristic of the SN1 mechanism?
Which type of substrate favors the SN1 mechanism?
What is a characteristic of electrophilic substitution?
What is a factor that affects nucleophilic substitution?
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What is the type of mechanism involved in SN2 reaction?
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What is the rate-determining step in the SN1 mechanism?
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What is the primary difference between nucleophilic and electrophilic substitution reactions?
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What is the role of the leaving group in a nucleophilic substitution reaction?
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How does the SN1 mechanism differ from the SN2 mechanism in terms of stereochemistry?
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What is the rate-determining step in the SN2 mechanism?
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What is the significance of carbocation stability in the SN1 mechanism?
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What is a key difference between alkyl halides and aromatic compounds in terms of substitution reactions?
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Study Notes
Substitution in Organic Chemistry
SN1 Mechanism
- Unimolecular nucleophilic substitution: a two-step mechanism
- Step 1: Formation of a carbocation intermediate (rate-determining step)
- Step 2: Nucleophile attacks the carbocation to form the product
- Characteristics:
- First-order kinetics (rate depends on substrate concentration)
- Racemic mixture of products (no stereospecificity)
- Rearrangement of the carbocation possible
- Favoured by:
- Tertiary alkyl halides
- Polar solvents
- High temperatures
SN2 Mechanism
- Bimolecular nucleophilic substitution: a one-step mechanism
- Concerted mechanism: nucleophile attacks from the backside of the leaving group
- Characteristics:
- Second-order kinetics (rate depends on substrate and nucleophile concentrations)
- Inversion of stereochemistry at the reaction center
- No carbocation intermediate
- Favoured by:
- Primary alkyl halides
- Good nucleophiles (e.g., NH₃, CN⁻)
- Aprotic solvents
Electrophilic Substitution
- Aromatic substitution: replacement of a hydrogen atom on an aromatic ring
- Electrophile: a species that accepts an electron pair (e.g., NO₂⁺, Cl₂)
- Mechanism: electrophile attacks the aromatic ring, forming a carbocation intermediate
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Types of electrophilic substitution:
- Nitration (NO₂⁺)
- Halogenation (Cl₂, Br₂)
- Sulfonation (SO₃H)
- Friedel-Crafts alkylation (R⁺)
Nucleophilic Substitution
- Replacement of a leaving group by a nucleophile
- Nucleophile: a species that donates an electron pair (e.g., OH⁻, CN⁻)
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Types of nucleophilic substitution:
- Aliphatic substitution (e.g., SN1, SN2)
- Aromatic substitution (e.g., nucleophilic aromatic substitution)
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Factors affecting nucleophilic substitution:
- Nucleophile strength
- Leaving group ability
- Solvent effects
- Steric and electronic factors
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Description
Test your understanding of substitution reactions in organic chemistry, including SN1, SN2, and electrophilic substitution mechanisms. Learn about the characteristics, factors, and types of each reaction.
