Mechanisms

Question 1

Reagents: HX

Answer 1

HydroHalide Addition to Pi Bond

• Markovnikov Regiochemistry
• Carbocation Rearrangement

Question 2

Reagents: Weak Nucleophile, Strong Acid Catalyst (Typically H₂O, H₃O⁺)

Answer 2

Acid-Catalyzed Hydration of Pi Bond - Markovnikov Regiochemistry - Carbocation Rearrangement

Question 3

Reagents: 1) Hg(OAc)2, HOH, THF

2) NaBH4

Answer 3

Oxymercuration / Demercuration

• Markovnikov Regiochemistry
• Anti/Trans Stereochemistry
• No Carbocation Rearrangement

Question 4

Reagents: 1) Hg(OAc)₂, HOR, THF

2) NaBH₄

Answer 4

Alkoxymercuration / Demercuration

• Markovnikov Regiochemistry
• Anti/Trans Stereochemistry
• No Carbocation Rearrangement

Question 5

Reagents: 1) BH₃, THF

2) H₂O₂, NaOH, H₂O

Answer 5

Hydroboration Oxidation

• Anti-Markovnikov Regiochemistry
• Syn / Cis Stereochemistry
• Carbocation Rearrangement

Question 6

Reagents: HX, ROOR (peroxides), heat or light

Answer 6

Anti-Mark HydroHalide Addition to Pi Bond

• Anti-Markovnikov Regiochemistry
• Carbocation Rearrangement

Question 7

Reagents: Br₂ or Br₂, HOR

Answer 7

Electrophilic Addition of Br₂ to Pi Bond (Bromonium Ion)

• Markovnikov Regiochemistry
• Anti / Trans Stereochemistry
• No Carbocation Rearrangement

Question 8

Reagents: Peroxy Acid (ROOOH) (Typically MCPBA)

Answer 8

Epoxide Ring Formation

Question 9

Reagents: 1) MCPBA

2) H⁺, HOR

Answer 9

Epoxide Ring Opening (Acidic Conditions)

• Markovnikov Regiochemistry (follows the carbocation)
• Anti / Trans Stereochemistry
• No Carbocation Rearrangement
• Can Add 2 OH or 1 OH & 1 OR Group

Question 10

Reagents: 1) MCPBA

2) Strong Base (HOR, NR₂^-, NaR)
3) Dilute Acid or RX

Answer 10

Epoxide Ring Opening (Basic Conditions)

• Anti-Markovnikov Regiochemistry (goes for spot with less steric hindrance)
• Anti / Trans Stereochemistry
• Can Add 2 OH, 2 OR, or 1 OH & 1 OR Group

Question 11

Reagents: CHCl₃, KOH or CH₂I₂, Zn(Cu)

Answer 11

Cyclopropane Ring from a Pi Bond

• Carbene addition to the pi bond
• Carbenes need to be made in situ

Question 12

Reagents: H₂, Pt or Pd metal

Answer 12

Strongly Catalyzed Reduction of Pi Bonds

• Syn / Cis Stereochemistry
• Reduces all Pi Bonds in Alkenes and Alkynes

Question 13

Reagents: H₂, Ni₂B or H₂, Lindlar Catalyst

Answer 13

Weakly Catalyzed Reduction of Pi bonds

• Syn / Cis Stereochemistry
• Only Reduces first Pi Bond in Alkenes and Alkynes

Question 14

Reagents: Na metal, NH₃ liquid

Answer 14

Weakly Catalyzed Reduction of Pi Bonds

• Anti / Trans Stereochemistry
• Only Reduces first Pi Bond in Alkenes and Alkynes

Question 15

Reagents: PCC

Answer 15

Oxidation of Primary Alcohol to Aldehyde

• Removes two H’s to form double bond across C-O
• Weaker oxidizing agent

Question 16

Reagents: KMnO₄ or Na₂Cr₂O₇, acid, water or CrO₃, acid, water

Answer 16

Oxidation of Secondary Alcohol to Ketone or Oxidation of Aldehyde to Carboxylic Acid

• Removes two H’s to form double bond across C-O
• Oxidizes vinyl H’s on Aldehydes into OH’s
• Stronger oxidizing agents

Question 17

Reagents: 1) OsO₄

2) H₂O₂ or NaHSO₃

Answer 17

Syn Addition of 2 OH’s to a Pi Bond

• Syn / Cis Stereochemistry
• No epoxide ring necessary to get similar product

Question 18

Reagents: 1) O₃ (ozone)

2) Zn, acetic acid

Answer 18

Ozonolysis

• Oxidative Cleavage of Sigma and Pi Bond
• “Cauterized” by oxygen molecule to create two new molecules
• Weak oxidizing agent, so vinyl H’s are untouched

Question 19

Reagents: 1) hot KMnO₄

2) H₃O⁺, H₂O

Answer 19

Permanganate

• Oxidative Cleavage of Sigma and Pi Bond
• “Cauterized” by oxygen molecule to create two new molecules
• Strong oxidizing agent, so vinyl H’s are oxidized into OH’s

Question 20

Reagents: Excess HX

Answer 20

HX Addition to Alkynes

• Markovnikov Regiochemistry
• Creates Geminal Dihalide (adds on same C)

Question 21

Reagents: Excess X₂

Answer 21

X₂ Addition to Alkynes

• Markovnikov Regiochemistry
• Anti / Trans Products
• Creates Geminal Tetrahalides (adds on same 2 C’s)

Question 22

Reagents: H₃0⁺, Vinyl Alcohol (OH on a C=C)

Answer 22

Tautomerization

• The Enol form (vinyl alcohol) shifts to it’s more stable Keto form (ketone with C=O)
• Reversible
• Exception to stability is phenols (benzylic more stable than allylic)

Question 23

Reagents: Catalytic Acid, H₂O or H₂SO₄ or HgSO₄ (+ Alkyne)

Answer 23

Acid-Catalyzed Hydration of Alkyne

• Markovnikov Regiochemistry
• Produces an Enol that tautomerizes into a Ketone

Question 24

Reagents: 1) BH₃, THF (+ Alkyne)

2) H₂0₂, NaOH, H₂O

Answer 24

Hydroboration Oxidation of Alkyne

• Anti-Markovnikov Regiochemistry
• Syn / Cis Stereochemistry
• Produces an Enol that tautomerizes into a Ketone

Question 25

Reagents: NaNH₂

Answer 25

Produces Acetylide Anion

• Deprotonates an Alkyne to create a nucleophile

Question 26

Reagents: H₂O, H₂SO₄ (+ Nitrile)

Answer 26

Nitrile Hydrolysis

• Like other alkynes, this creates an Enol product that tautomerizes to a Ketone