Preparation of Aldehydes and Ketones 🌟

1  Carbonyl Snapshot 🔍

The carbonyl carbon is sp²-hybridised and lies in one plane with its three neighbors. Its leftover p-electron overlaps with oxygen’s p-orbital to form a π-bond, giving a trigonal-planar shape with bond angles close to 120°, and a strong C=O dipole. Because oxygen is more electronegative, the carbonyl carbon acts as an electrophile (Lewis acid) while the oxygen behaves as a nucleophile (Lewis base). 😎

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2  General Routes to Both Aldehydes & Ketones

2.1 Oxidation of Alcohols 🔥

• Primary alcohol → aldehyde
• Secondary alcohol → ketone

$$ \text{R-CH}_2\text{OH} \;\xrightarrow{[O]}\; \text{R-CHO} \qquad \text{R}_2\text{CH-OH} \;\xrightarrow{[O]}\; \text{R}_2\text{C=O} $$

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2.2 Dehydrogenation of Alcohols ⚡

Vaporise the alcohol and pass it over Ag or Cu metal at high temperature. Primary alcohol → aldehyde; secondary alcohol → ketone.

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2.3 From Hydrocarbons 🧪

1. Ozonolysis of Alkenes $$ \text{Alkene} + \text{O}_3 \;\xrightarrow[\text{H}_2\text{O}]{\text{Zn}} \; \text{Aldehydes / Ketones} $$ The products depend on the double-bond substitution pattern.
2. Hydration of Alkynes Ethyne + H₂SO₄/HgSO₄ → acetaldehyde; any other alkyne gives a ketone through enol–keto tautomerism.

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3  How to Make Aldehydes Only 🌼

3.1 Rosenmund Reduction

Acyl chloride + H₂, Pd/BaSO₄ → aldehyde $$ \text{R-COCl} + \text{H}_2 \;\xrightarrow{\text{Pd/BaSO}_4}\; \text{R-CHO} + \text{HCl} $$

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3.2 Stephen Reaction

Nitrile + SnCl₂/HCl → imine → hydrolyze → aldehyde
🎯 Mild and selective!

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3.3 DIBAL-H Reduction

Di-iso-butylaluminium hydride (DIBAL-H) trims nitriles or esters down to aldehydes at low temperature.

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3.4 Making Aromatic Aldehydes

• Etard reaction – Chromyl chloride (CrO₂Cl₂) oxidises a side-chain –CH₃ of toluene to the formyl group.
• CrO₃/Ac₂O – Forms benzylidene diacetate, then water gives benzaldehyde.
• Side-chain chlorination + hydrolysis – Toluene → benzal chloride → benzaldehyde.
• Gattermann–Koch – Benzene + CO + HCl, AlCl₃/CuCl cat. → benzaldehyde.

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4  How to Make Ketones Only 🏆

4.1 From Acyl Chlorides (Cd Reagent)

React an acyl chloride with dialkylcadmium (R′₂Cd) formed in situ from a Grignard reagent and CdCl₂. $$ \text{R-COCl} + \text{R′}_2\text{Cd} → \text{R-CO-R′} + \text{R′CdCl} $$

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4.2 From Nitriles (Grignard Route)

Nitrile + RMgX → imine-MgX complex → hydrolyze → ketone.

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4.3 Friedel-Crafts Acylation (Aromatic Ketones)

Benzene + acyl chloride, AlCl₃ → aryl ketone.

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5 High-Yield NEET Nuggets 🎯

1. Rosenmund Reduction – clean route to aldehydes from acyl chlorides.
2. Stephen Reaction – converts nitriles to aldehydes without over-reduction.
3. Etard Reaction – handy trick to stop oxidation of toluene at the aldehyde stage.
4. Gattermann–Koch Formylation – one-step synthesis of benzaldehyde from benzene.
5. Friedel-Crafts Acylation – go-to method for aryl ketones.

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You’ve got this! Keep practicing, and those reactions will stick. 🚀