Reactions

Question 1

Sn1

Answer 1

• unimolecular (nucleophile not involved in rate determining step)
  -occurs by racemization
• Must be polar protic solvent
• Weak nucleophile
• Benzylic and Allylic react the best, aryl, methyl, vinyl, and 1º don’t react
• Occurs between substrate and nucleophile
• Can form carbocation rearrangements

Question 1

Sn2

Answer 1

• bimolecular (both nucleophile and electrophile involved in rate determining step)
• occur by inversion
• leaving group must be more stable than the nucleophile
• Moderate strong nucleophile
• Prefers polar aprotic solvent
• In polar aprotic solvent, nucleophilicity and basicity are the same, except if the base is sterically hindered
• In polar protic solvent, nucleophilicity and basicity are the same unless the base is sterically hindered AND the size trend is reversed.
• Allylic and Benzylic react the best, 3º, aryl, and vinyl don’t react
• Cannot form carbocation rearrangements

Question 2

E2

Answer 2

• Bimolecular (both nucleophile and electrophile involved in rate determining step)
• Occurs between substrate and base
• E2 zaitsev is more stable (more substituents on alkene)
• E2 hoffman forms with bulky base (less substituents on alkene)
• Can occur with any electrophile, however lower degrees prefer Sn2 since it is lower in energy
• For 2º electrophiles, E2 promoted by bulky base or N/O unstabilized anions
• Cannot form carbocation rearrangements

Question 3

E1

Answer 3

• unimolecular (nucleophile not involved in rate determining step)
• E1 will always be zaitsev due to the formation of a carbocation intermediate
• Can form carbocation rearrangements
• Only formed exclusively when an alcohol is treated with concentrated acid, usually minor with Sn1 as major

Question 4

Steps To Determine Reaction Type

Answer 4

1. Put full and partial charges on all atoms
2. Determine the attacking species (nuc or base) and the species that can accept protons (electrophile or acid)
3. Classify the electrophile as methyl, primary, secondary, or tertiary, allylic, or benzylic
4. Classify the attacking species as a strong or weak nuc
5. Classify the attacking species as a strong or weak base
6. Classify the attacking species as stericaly hindered or unhindered
7. Classify the solvent as polar protic, polar aprotic, or apolar

Question 5

Hydrohalogenation

Answer 5

• Occurs with an alkene as the electrophile
• Addition of hydrogen and halogen
• Unimolecular (nucleophile not involved in rate determining step)
• Carbocation forms on carbon with most substituents
• Halogen bonds to carbocation
• Hydrogen bonds to other carbon
• Product forms via racemization

Question 6

Hydration

Answer 6

• Occurs with an alkene as the electrophile
• Addition of H and OH
• Requires a strong acid, not just water
  -Unimolecular (nucleophile not involved in rate determining step)
• Carbocation forms on carbon with most substituents
• OH bonds to carbocation
• Hydrogen bonds to other carbon
• Product forms via racemization

Question 7

Oxymercuration-Demercuration

Answer 7

• Occurs with an alkene as the electrophile
• Two separate steps
• Addition of HgOAc and OH, then Hg replaced with H
• No carbocation forms, no rearrangements
• nucleophile attacks more electrophilic carbon, one with more carbon substituents
• Forms two intermediates due to front and back side attack from mercury
• Products form via racemization

Question 8

Hydroboration-Oxidation

Answer 8

• Occurs with an alkene as the electrophile
• Addition of OH and H via BH3THF
• Hydrogen atom adds to more substituted carbon
• Products form via racemization

Question 9

Alkene Reactions

Answer 9

Addition TO Alkenes
- Hydrohalogenation
- Hydration
- Oxymercuration-Demercuration
- Hydroboration-Oxidation
- Halogenation
- Halohydrin Formation
- Epoxidation
- Hydrogenation
- Dihydroxylation
- Anti-Markovnikov Hydrohalogenation (Radical)
Oxidative Cleavage OF Alkenes