SN1 - Reaction Energy Diagram

tert-Butyl Alcohol to tert-Butyl Chloride

This interactive diagram shows the Potential Energy Surface (PES) for the S_N1 reaction of tert-butyl alcohol with HCl to form tert-butyl chloride. Hover over the structures, arrows or points on the graph to learn more about each stage of the reaction. Consider the questions posed as you explore.

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Step 1: Protonation of tert-Butyl Alcohol
- Hover over tert-butyl alcohol: "This is our starting material, tert-butyl alcohol and notice where it appears on the PES. Consider: What makes the oxygen atom a good site for protonation?"
- Hover over the protonated tert-butyl alcohol: "This is the protonated tert-butyl alcohol. Consider: Why is the oxygen now a better leaving group?"
Step 2: Loss of Leaving Group (Carbocation Formation)
- Hover over the transition state leading to the carbocation: "This transition state represents the loss of the leaving group (water). Consider: This is the rate-determining step (RDS). Why is this step the RDS? What factors contribute to the height of this energy barrier?"
- Hover over the tert-butyl carbocation: "This is the tert-butyl carbocation intermediate. Consider: Why is this carbocation relatively stable? What are the factors that contribute to carbocation stability (hyperconjugation, inductive effects)?"
- Hover over the water molecule: "Water, the leaving group. Consider: How does water's departure affect the overall entropy of the system?"
Step 3: Nucleophilic Attack by Chloride Ion
- Hover over the transition state for nucleophilic attack: "This transition state represents the attack of the chloride ion on the carbocation. Consider: Why is this step faster than the loss of the leaving group? Is the chloride a good nucleophile? Why or why not?"
- Hover over tert-butyl chloride: "This is our final product, tert-butyl chloride. Consider: Compare the energy of the starting material and the product. Is this reaction endothermic or exothermic? Overall, what drives this reaction forward?"

Question: The answers to the above questions can be found here!

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Step 1: Protonation of tert-Butyl Alcohol
- This is our starting material, tert-butyl alcohol. Consider: What makes the oxygen atom a good site for protonation?
  The oxygen atom has lone pairs of electrons, making it a Lewis base and able to accept a proton (H⁺).
- This is the protonated tert-butyl alcohol. Consider: Why is the oxygen now a better leaving group?
  Protonation converts the -OH group to -OH₂⁺, which is a much better leaving group because it forms a stable water molecule upon departure.
Step 2: Loss of Leaving Group (Carbocation Formation)
- This transition state represents the loss of the leaving group (water). Consider: This is the rate-determining step (RDS). Why is this step the RDS? What factors contribute to the height of this energy barrier?
  The formation of the carbocation is the RDS because it involves breaking a C-O bond, which requires more energy than proton transfer. The energy barrier is high due to the instability of the developing carbocation and the energy needed to break the C-O bond.
- This is the tert-butyl carbocation intermediate. Consider: Why is this carbocation relatively stable? What are the factors that contribute to carbocation stability (hyperconjugation, inductive effects)?
  The tert-butyl carbocation is relatively stable due to hyperconjugation (overlap of C-H sigma bonds with the empty p-orbital) and inductive effects (electron donation from the alkyl groups), which delocalize the positive charge.
- Water, the leaving group. Consider: How does water's departure affect the overall entropy of the system?
  The departure of water increases the entropy (disorder) of the system, which favors the reaction.
Step 3: Nucleophilic Attack by Chloride Ion
- This transition state represents the attack of the chloride ion on the carbocation. Consider: Why is this step faster than the loss of the leaving group? Is the chloride a good nucleophile? Why or why not?
  The nucleophilic attack is faster because the carbocation is highly reactive (electrophilic) and the chloride ion is a good nucleophile (negatively charged, lone pairs). The energy barrier for this step is lower than the carbocation formation.
- This is our final product, tert-butyl chloride. Consider: Compare the energy of the starting material and the product. Is this reaction endothermic or exothermic? Overall, what drives this reaction forward?
  The product (tert-butyl chloride) is lower in energy than the starting material (tert-butyl alcohol), so the reaction is exothermic (ΔG < 0). The reaction is driven forward by the formation of the stable tert-butyl chloride and the favorable entropy change associated with the release of water.