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Questions and Answers
What is formed when carbon is attacked by a nucleophile in this process?
What is formed when carbon is attacked by a nucleophile in this process?
- Isocyanide (correct)
- Carbocation
- Nitrite ion
- Halide ion
Which of the following acts as a leaving group in the S₁ mechanism?
Which of the following acts as a leaving group in the S₁ mechanism?
- Nucleophile
- Nitrogen
- Isocyanide
- Halogen atom (correct)
In an S₂ reaction, how does the nitrite ion behave as a nucleophile?
In an S₂ reaction, how does the nitrite ion behave as a nucleophile?
- Attacks only through oxygen
- Always forms a carbocation
- Attacks through either O or N (correct)
- Does not form any bonds
What happens to the bond pair of electrons during the leaving process of the halogen?
What happens to the bond pair of electrons during the leaving process of the halogen?
How many changes does the substrate undergo during an S₁ reaction?
How many changes does the substrate undergo during an S₁ reaction?
Which factor primarily influences nucleophilicity in a solvent?
Which factor primarily influences nucleophilicity in a solvent?
What is the relationship between carbocation stability and nucleophilicity?
What is the relationship between carbocation stability and nucleophilicity?
What type of bond is formed when a nucleophile attacks an electrophilic carbon?
What type of bond is formed when a nucleophile attacks an electrophilic carbon?
In the context of an S₂ mechanism, how is the leaving group characterized?
In the context of an S₂ mechanism, how is the leaving group characterized?
Which step is critical for the formation of isocyanide in the mechanism described?
Which step is critical for the formation of isocyanide in the mechanism described?
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Study Notes
Nucleophilic Substitution Mechanisms
- The S_N2 reaction occurs more rapidly in polar protic solvents compared to aprotic solvents.
Polar Protic vs. Aprotic Solvents
- Polar protic solvents can stabilize nucleophiles through solvation, which can decrease the reaction rate of S_N2.
- Aprotic solvents or low-polarity solvents enhance nucleophilic character, favoring the S_N2 mechanism.
Nucleophile and Base Definitions
- A nucleophile is a species that donates an electron pair to form a bond, while a base accepts protons (H⁺).
- The role of a solvent is critical in stabilizing nucleophiles, affecting their reactivity.
Reaction Rates and Mechanisms
- Tertiary halides undergo nucleophilic substitution primarily through the S_N1 mechanism, while primary halides typically follow the S_N2 mechanism.
- Secondary halides may react via either mechanism, dependent on specific conditions.
Resonance Stabilization
- Resonance stabilization of allylic and benzylic carbocations can influence reaction pathways and rates of substitution.
Nucleophilicity Factors
- The nucleophilicity of reagents is affected by solvent polarity and the ability of the solvent to solvate anions.
- Protic solvents enhance anion solvation through hydrogen bonding, making nucleophiles more effective.
Examples of Nucleophiles
- Ambident nucleophiles such as nitrite (NO₂⁻) can react through either oxygen (O) or nitrogen (N) sites to form new bonds.
Reaction Mechanism Overview
- During an S_N2 reaction, the halogen atom acts as the leaving group, departing with the bond pair of electrons.
- The transition from substrate to product involves significant changes, with new bonds formed at the electrophilic carbon.
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