4.4.2 Reaction mechanisms

• Understanding reaction mechanisms allows chemists to optimize reaction conditions
• Match the reaction mechanism with its characteristic:

  SN1 ↔️ Two-step process with carbocation

  SN2 ↔️ Single-step process with backside attack

  E1 ↔️ Two-step elimination with carbocation

  E2 ↔️ Single-step concerted elimination
• Nucleophiles possess a negative charge or lone pairs
• Why is understanding reaction mechanisms crucial in organic synthesis?

  Predict, optimize, design reactions
• Understanding reaction mechanisms allows chemists to predict the products of a reaction.

  True
• Nucleophilic substitution (SN1) occurs with tertiary or benzylic carbocations
• What does understanding reaction mechanisms help chemists design?

  Synthetic routes
• Optimizing reaction conditions is one of the benefits of understanding reaction mechanisms.


  True
• Elimination reactions involve the removal of atoms or groups to form a π-bond
• Match the reaction mechanism with its characteristic:

  SN1 ↔️ Two-step process

  SN2 ↔️ Backside attack

  E1 ↔️ Carbocation intermediate

  E2 ↔️ Concerted removal of leaving group and H
• Steps in the electrophilic addition mechanism

  1️⃣ Electrophile attacks the π-bond

  2️⃣ Carbocation intermediate is formed

  3️⃣ Nucleophile attacks the carbocation
• In the SN1 mechanism, the leaving group departs to form a carbocation
• Steps in the SN2 mechanism

  1️⃣ Nucleophile attacks from the backside

  2️⃣ Leaving group departs
• The SN1 mechanism occurs with tertiary or benzylic carbocations because they stabilize the intermediate
• Steps in the electrophilic addition mechanism

  1️⃣ Electrophile attacks the π-bond

  2️⃣ Carbocation intermediate forms

  3️⃣ Nucleophile attacks the carbocation
• What is a reaction mechanism in organic synthesis?

  Step-by-step reaction description
• Electrophilic addition involves the addition of an electrophile to a π-bond.


  True
• What is a nucleophile in organic chemistry?

  Electron-rich species
• Electrophiles are electron-deficient species that accept electron pairs.


  True
• A reaction mechanism is a step-by-step description of how a chemical reaction occurs at the molecular level
• Steps in the electrophilic addition mechanism

  1️⃣ Electrophile attacks the π-bond
• SN2 reactions involve a planar carbocation intermediate.

  False
• A reaction mechanism is a step-by-step description of how a chemical reaction occurs at the molecular level
• What is an example of electrophilic addition in a reaction mechanism?

  HBr to propene
• SN1 reactions occur in a single step.

  False
• A nucleophile is an electron-rich species that donates electron pairs
• Electrophiles are electron-deficient species that accept electron pairs.


  True
• The SN1 mechanism involves a carbocation intermediate.


  True
• SN2 reactions involve backside attack of the nucleophile on the carbon bearing the leaving group.


  True
• What intermediate is formed in the first step of the SN1 mechanism?

  Carbocation
• In the SN2 mechanism, the nucleophile attacks the carbon bearing the leaving group from the front.

  False
• What is an example of a product formed in the electrophilic addition of HBr to propene?

  2-bromopropane
• The SN2 mechanism occurs in a single concerted step.
• What type of bond is formed in the E1 mechanism after a base removes a hydrogen?

  π-bond
• The E2 mechanism occurs with tertiary alkyl halides.

  False
• What type of carbocation is formed in the SN1 mechanism?

  Planar carbocation
• The E2 mechanism involves the concerted removal of a hydrogen and the leaving group.
• With what type of alkyl halides does the E2 mechanism occur?

  Primary or secondary
• The SN2 mechanism occurs with tertiary alkyl halides.

  False
• In the E2 mechanism, the base removes a hydrogen concurrently with the departure of the leaving group.