Aldehydes / Ketones Flashcards
(24 cards)
🌟 1. Basic Info / Intro
Aldehydes: Have –CHO group.
Ketones: Have –CO– group between two carbon atoms.
General formula:
Aldehyde: R–CHO
Ketone: R–CO–R’
🌟 2. Preparation of Aldehydes and Ketones
✅ (i) Oxidation of Alcohols
Primary alcohol (R–CH₂OH) → mild oxidation → Aldehyde (R–CHO)
Secondary alcohol (R₂–CHOH) → oxidation → Ketone (R₂–CO)
Reagents: Acidified potassium dichromate (K₂Cr₂O₇/H⁺) or potassium permanganate (KMnO₄)
Condition: Heat (∆)
✅ (ii) From Phthalic acid (For phthalaldehyde)
What are aldehydes and ketones?
Aldehydes: R-CHO (terminal C=O).
Ketones: R-CO-R’ (internal C=O).
Key Difference: Aldehydes oxidize easily; ketones resist oxidation.
How to prepare aldehydes/ketones?
Oxidation of alcohols:
Primary Alcohol → Aldehyde: R-CH₂OH → R-CHO (K₂Cr₂O₇/H₂SO₄, distillation).
Secondary Alcohol → Ketone: R₂CHOH → R₂CO (K₂Cr₂O₇/H₂SO₄, reflux).
Ozonolysis of alkenes: Breaks double bonds to form carbonyls.
🌟 3. Nucleophilic Addition Reactions
✅ (i) Base-Catalyzed Nucleophilic Addition (General Mechanism)
Base attacks carbonyl carbon → forms alkoxide intermediate → protonation → alcohol.
Base-catalyzed nucleophilic addition (general mechanism)?
Step 1: Base (e.g., CN⁻) attacks δ⁺ carbonyl carbon.
Step 2: Protonation of intermediate.
Example:
R-CHO + CN⁻ → R-CH(OH)-CN (Cyanohydrin).
Acid-catalyzed nucleophilic addition (general mechanism)?
Step 1: H⁺ protonates carbonyl oxygen.
Step 2: Nucleophile attacks δ⁺ carbon.
Example:
R-CO-R’ + H₂O → R-C(OH)₂-R’ (Hydrate).
(ii) Addition of Hydrogen Cyanide (HCN)
Reaction:
R–CO–R’ + HCN → R–C(OH)(CN)–R’
Conditions: HCN in presence of base (like NaOH)
Base generates CN⁻ nucleophile.
✅ (iii) Haloform Reaction (Specifically for methyl ketones)
R–CO–CH₃ + 3X₂ + 4OH⁻ → R–COO⁻ + CHX₃ + 3X⁻ + 3H₂O
(Where X = Cl, Br, I)
Condition: Warm aqueous base.
✅ (iv) Acid-Catalyzed Nucleophilic Addition (General Mechanism)
Protonate carbonyl oxygen → increases electrophilicity → nucleophile attacks → forms addition product
🌟 4. Reaction with 2,4-Dinitrophenylhydrazine (Brady’s Reagent)
Reaction:
R–CO–R’ + H₂NNH–(NO₂)₂ → R–C=N–NH–(NO₂)₂–R’ + H₂O
Condition: Room temp.
Observation: Bright orange or yellow precipitate = positive test!
🌟 5. Reduction of Aldehydes and Ketones
✅ (i) With Hydrides
Reagent: LiAlH₄ (dry ether) or NaBH₄ (aqueous/alcoholic medium)
Aldehyde Reduction:
R–CHO + 2[H] → R–CH₂OH
Ketone Reduction:
R–CO–R’ + 2[H] → R–CHOH–R’
🌟 6. Reaction with Hydrogen Cyanide Again (Detailed)
✅ Step 1:
CN⁻ attacks C=O, breaking the pi bond.
✅ Step 2:
O⁻ intermediate grabs H⁺ from solvent → forms cyanohydrin.
🌟 7. Reaction with Primary Nitrogen Nucleophiles
Example:
Reaction with ammonia (NH₃) → imine formation.
Reaction with hydrazine (NH₂–NH₂) → hydrazone formation.
General Reaction:
R–CO–R’ + NH₂–R’’ → R–C=NR’’ + H₂O
🌟 8. Oxidation Reactions
✅ (i) Oxidation of Aldehydes
Reagents:
Fehling’s Solution (Cu²⁺) — Brick red ppt of Cu₂O
Tollens’ Reagent ([Ag(NH₃)₂]⁺) — Silver mirror (Ag)
Reaction (with Tollens):
R–CHO + 2[Ag(NH₃)₂]⁺ + 3OH⁻ → R–COO⁻ + 2Ag + 4NH₃ + 2H₂O
✅ (ii) Oxidation of Ketones
Generally resistant!
Under strong conditions → breaks into carboxylic acids.
🌟 9. Tests to Distinguish Aldehydes and Ketones
✅ (i) Fehling’s Solution Test
Aldehydes give brick red Cu₂O precipitate.
Ketones = No reaction.
✅ (ii) Tollens’ Test (Silver Mirror Test)
Aldehydes form a silver mirror (metallic silver).
Ketones = No silver mirror.
Haloform Reaction (e.g., iodoform test)?
Reagents: I₂ + NaOH (warm).
Works For: Methyl ketones (R-CO-CH₃) or ethanol.
Observation: Yellow CHI₃ precipitate.
Front: Reaction with NH₃ derivatives (e.g., NH₂OH)?
Back:
Products:
NH₂OH → Oxime (R-CH=N-OH).
NH₂-NH₂ → Hydrazone (R-CH=N-NH₂).
- Key Mnemonics
Oxidation: “Aldehydes Acidify, Ketones Kick back.”
Tests: “Tollens’ = Thin silver layer; Fehling’s = Fiery red.”
What Are yo planz know
LEAVE EVERYTHING and fouces .
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