Intro - 1,2 Addition Reactions

Overview of Reactions Discussed

• Introduction of different chemical reactions previously covered
  • Acid-base reactions.
  • Radical reactions (not revisiting).
  • Substitutions and eliminations (Chapters 7A and 7B).
• Focus on reactions concerning carbonyl compounds.

Context and Relevance of Carbonyl Chemistry

• This chapter introduces carbonyl functional groups.
• Foundational knowledge includes:
  • Alkyls, alkenes, alkynes (CH-based functional groups).
  • Amines and alcohols (single-bonded heteroatoms like O and N).
  • C=O functional groups: carbonyl compounds (Aldehydes and Ketones).
• Emphasis on carbonyl compounds links to future biochemistry courses.

Carbonyl Compounds Overview

• Definition of the carbonyl group: $C=O$
• Carbon-oxygen bond properties:
  • Polarization towards the oxygen leading to partial charges:
  • Partial negative on the oxygen.
  • Partial positive on the carbon.
• Carbonyl as an electrophile analogous to carbon in SN2 reactions due to its positive charge.

Reactivity Trends of Carbonyl Compounds

Series of Carbonyl Derivatives

• Left to right reactivity trend from acid halide to amide:
  • Acid Halide >> Aldehyde/Ketone >> Carboxylic Acid/Ester >> Amide.

Acid Halides

• Most reactive among carbonyl derivatives.
• Strong polarization due to adjacent electronegative halogen.

Aldehydes and Ketones

• Both have similar reactivity; act as baseline for comparison;
• Reactive due to resonance stabilization but less so than acid halides.

Carboxylic Acids and Esters

• Stabilization through resonance involving the adjacent oxygen decreases reactivity.

Amides

• Least reactive due to even better resonance stabilization of the carbonyl carbon through the adjacent nitrogen.

Mechanistic Details of Reactions with Carbonyls

• Key Mechanism: NucleophilicAttackon_Carbonyl
  • Nucleophile attacks the partially positive carbonyl carbon.
  • Generates a tetrahedral intermediate (sp3 hybridization).
• Retention of carbonyl reactivity trends as stabilization increases for less reactive compounds.

One-Two Addition Mechanism

Terminology:

• "One-Two Addition": Refers to addition at the carbonyl carbon and subsequently on another position (like an electrophilic carbon).
• "In Up Down Out": Describes the movement of electrons during nucleophilic attack: electrons from nucleophile move in, pi electrons go up, and the electrons on the leaving group go out.

Steps Involved in One-Two Addition

1. Addition of Nucleophile:
   • Strong nucleophile (like $NaOH$ or alcohol) attacks the carbonyl carbon.
2. Formation of Tetrahedral Intermediate:
   • Shift in hybridization leads the carbon to become sp3.
3. Deprotonation:
   • Neutralizes positive charge formed on oxygen.
4. Click out leaving group:
   • Stabilize resulting molecule through involvement of electron withdrawing groups.

• Mechanistic Overview: repeat actions and conditions may vary.

Consideration of Acid-Base Chemistry

Acidic vs. Basic Conditions

• Acidic Conditions:
  • Protonation of oxygen before nucleophilic attack.
  • Positively charged oxygens are permitted under acidic conditions.
• Basic Conditions:
  • Nucleophiles like $NH_3$ or strong bases can directly attack the carbonyl without prior protonation.
  • May stabilize carbocations; however, attention must be paid to the pKa to avoid instability.

Example: Reactions Under Acidic Conditions with Alcohol and NH3

• Using alcohol (like methanol) or other nucleophiles serves to derive different products based on acidic proclivities.
• Selectivity of base derived can cause further modifications.

Redox Chemistry in Relation to Additions

• Redox Overview:
  • General remembering: Loss of $C-H$ bonds signifies oxidation, while gain signifies reduction.
• For carbonyls:
  • Always assess the carbon’s role through interactions with nucleophiles – increase in $C-O$ signifies oxidation.
• Carbon group oxidations are resulted in general end products of specific carbons leading to directed functioning of molecules in a targeted reaction pathway.

Final Remarks & Wrap Up

• Continuous interaction facilitates diverse reactivity patterns among the functional derivatives discussed.
• Emphasis on reactivity trends and mechanisms will enhance student comprehension of subsequent organic chemistry.
• Safety Considerations:
  • Lithium Aluminum Hydride (LAH) reaction dynamics are dangerous; anecdotal evidence of lab accidents must be noted.
• Understanding conditions is crucial in yielding safe and correct reactions in organic chemistry.