Organic Chemistry Mechanisms Overview

Introduction

• Presenter: Leah from leah4sci.com
• Focus: Simple organic chemistry mechanisms and arrow patterns
• Series: Part 3
  • Part 1 & 2 covered common pattern types: nucleophilic attack, loss of a leaving group, proton transfer, rearrangement
• Reference: Series available on leah4sci.com/mechanism

SN1 Reaction: 2-Butanol and Hydrochloric Acid

Reaction Overview

• Reaction Type: SN1 reaction
• Reactants: 2-butanol and hydrochloric acid
• Focus: Understanding arrow patterns and electron movement

Mechanism Steps

1. Proton Transfer:

   • OH group on 2-butanol protonated to form a good leaving group (OH2+)
   • Oxygen uses lone pair to grab hydrogen from HCl, breaking H-Cl bond
   • Intermediate formed: Oxygen with two hydrogens, one lone pair, charge +1; Cl- with charge -1

2. Loss of Leaving Group:

   • OH2+ group leaves, taking electrons with it
   • Forms a carbocation on the carbon chain
   • Oxygen becomes neutral with two lone pairs

3. Nucleophilic Attack:

   • Cl- attacks carbocation, forming a bond with carbon
   • Final product: Substitution of OH with Cl

Alkene and Sulfuric Acid in Methanol

Reaction Overview

• Reactants: Alkene, sulfuric acid, methanol
• Type: Acid-catalyzed hydration with alcohol

Mechanism Steps

1. Proton Transfer (Initial Activation):

   • Sulfuric acid dissociates, transferring a proton to methanol
   • Methanol becomes protonated, now a positive charge

2. Nucleophilic Attack:

   • Alkene pi bond electrons attack protonated methanol
   • Pi bond breaks, hydrogen adds to less substituted carbon (Markovnikov's rule)
   • Form a carbocation on more substituted carbon

3. Carbocation Rearrangement:

   • Secondary carbocation rearranges to a more stable tertiary carbocation via hydride shift

4. Nucleophilic Attack:

   • Methanol attacks carbocation, forming a bond with tertiary carbon
   • Methanol has three bonds and one lone pair, becomes positive

5. Proton Transfer (Final Neutalization):

   • Another methanol deprotonates the intermediate, restoring neutrality
   • Final product is an ether

Conclusion

• Encouragement to review the entire series for confidence
• Additional resources: Organic Chemistry Study Hall on leah4sci.com/join