What is Carbocation Rearrangement: Mechanisms and Examples

📚 Carbocation Rearrangement: A Quick Study Guide

• ⚛️ Carbocations are positively charged carbon atoms with only six electrons. They are highly unstable and reactive.
• 🔄 Carbocation rearrangements occur to form a more stable carbocation. Stability order: tertiary > secondary > primary > methyl.
• 🚗 1,2-Hydride Shift: A hydrogen atom with its pair of electrons moves from an adjacent carbon to the carbocation.
• 🌲 1,2-Alkyl Shift: An alkyl group with its pair of electrons moves from an adjacent carbon to the carbocation.
• ⚡️ Rearrangements only occur if they lead to a more stable carbocation.
• 🌡️ The driving force for rearrangement is the relief of strain and the formation of a more stable carbocation intermediate.
• 📝 Example: A secondary carbocation rearranges to a more stable tertiary carbocation via a 1,2-hydride shift.

🧪 Practice Quiz

1. Which of the following statements is true regarding carbocation stability?
   1. A) Primary carbocations are more stable than tertiary carbocations.
   2. B) Secondary carbocations are more stable than primary carbocations.
   3. C) Methyl carbocations are the most stable.
   4. D) Carbocation stability is not dependent on the degree of substitution.
2. What is the primary driving force for carbocation rearrangement?
   1. A) To increase the steric hindrance around the carbocation.
   2. B) To decrease the electron density around the carbocation.
   3. C) To form a more stable carbocation.
   4. D) To break the octet rule.
3. In a 1,2-hydride shift, what moves from one carbon to another?
   1. A) A methyl group
   2. B) A hydrogen atom with its pair of electrons
   3. C) A hydroxyl group
   4. D) A lone pair of electrons
4. Which type of shift involves the movement of an alkyl group?
   1. A) 1,3-Alkyl shift
   2. B) 1,2-Hydride shift
   3. C) 1,2-Alkyl shift
   4. D) 1,3-Hydride shift
5. Which of the following carbocations is most stable?
   1. A) Methyl carbocation
   2. B) Primary carbocation
   3. C) Secondary carbocation
   4. D) Tertiary carbocation
6. A secondary carbocation is more likely to rearrange to which of the following?
   1. A) A primary carbocation
   2. B) A methyl carbocation
   3. C) A tertiary carbocation
   4. D) No rearrangement will occur.
7. What is the formal charge on a carbocation?
   1. A) -1
   2. B) 0
   3. C) +1
   4. D) +2