Aldehydes, Ketones and Carboxylic Acids: Complete Guide & Formula Sheet with Free PDF Download (JEE & NEET)
Aldehydes Ketones Carboxylic Acids — Competishun
Aldehydes, Ketones and Carboxylic Acids: Complete Guide & Formula Sheet with Free PDF Download (JEE & NEET)
Aldehydes, Ketones and Carboxylic Acids is one of the most important and scoring chapters in organic chemistry for JEE and NEET. It carries a weightage of 3-4% in JEE Main, with 3-4 questions appearing every year[reference:0]. This chapter is the bridge between basic organic chemistry and advanced reactions, and it is essential for understanding the chemistry of carbonyl compounds.
This chapter deals with compounds containing the carbonyl group (C=O). Aldehydes have the carbonyl group bonded to at least one hydrogen (R-CHO), Ketones have it bonded to two carbon atoms (R-CO-R'), and Carboxylic Acids have it bonded to a hydroxyl group (R-COOH)[reference:1]. These compounds are among the most important classes of organic compounds and are found everywhere in nature and industry.
This page gives you the complete guide to Aldehydes, Ketones and Carboxylic Acids with all concepts explained in depth. You will find clear definitions, nomenclature, preparation methods, reaction mechanisms, named reactions, acidity trends, and practice questions. Download the free PDF below and keep it handy for quick revision before your JEE Main, JEE Advanced, or NEET exam.
Download the Aldehydes, Ketones and Carboxylic Acids Complete Guide PDF
Get all Aldehydes, Ketones and Carboxylic Acids concepts, nomenclature, preparation methods, reactions, mechanisms, and named reactions in one clean PDF, free. Perfect for JEE and NEET revision.
Download Free PDFWhat are Aldehydes, Ketones and Carboxylic Acids?
These three classes of compounds are among the most important in organic chemistry. They are found in nature, in pharmaceuticals, in polymers, and in countless industrial applications. Understanding their chemistry is essential for any student of organic chemistry.
Aldehydes (R-CHO)
Carbonyl group bonded to at least one hydrogen. Examples: Formaldehyde (HCHO), Acetaldehyde (CH₃CHO), Benzaldehyde (C₆H₅CHO).[reference:4]
Ketones (R-CO-R')
Carbonyl group bonded to two carbon atoms. Examples: Acetone (CH₃COCH₃), Butanone (CH₃COCH₂CH₃), Cyclohexanone.[reference:5]
Carboxylic Acids (R-COOH)
Carbonyl group bonded to a hydroxyl group (-OH). Examples: Acetic acid (CH₃COOH), Benzoic acid (C₆H₅COOH).[reference:6]
Glossary of Terms — Complete A to Z
Before diving deep into each topic, let's understand the key terminology used in this chapter:
| Term | Definition |
|---|---|
| Carbonyl Group | The C=O functional group. The carbon is electrophilic, and the oxygen is nucleophilic. |
| Nucleophilic Addition | The characteristic reaction of aldehydes and ketones where a nucleophile adds to the carbonyl carbon.[reference:7] |
| α-Hydrogen | A hydrogen atom attached to the carbon adjacent to the carbonyl group. It is acidic and can be removed by a base. |
| Aldol Condensation | A reaction where two aldehydes or ketones with α-H undergo condensation to form a β-hydroxy carbonyl compound.[reference:8] |
| Cannizzaro Reaction | A reaction of aldehydes without α-H with concentrated base to give an alcohol and a carboxylic acid.[reference:9][reference:10] |
| Clemmensen Reduction | Reduction of carbonyl group to CH₂ using Zn-Hg and HCl.[reference:11] |
| Wolff-Kishner Reduction | Reduction of carbonyl group to CH₂ using hydrazine and KOH.[reference:12] |
| Hell-Volhard-Zelinsky (HVZ) Reaction | α-Bromination of carboxylic acids using red phosphorus and bromine.[reference:13] |
| Esterification | The reaction of a carboxylic acid with an alcohol to form an ester.[reference:14] |
| Mastering these terms is essential for understanding the chemistry of aldehydes, ketones, and carboxylic acids. | |
Nomenclature — IUPAC and Common Names
IUPAC Nomenclature
| Compound Class | Parent Chain | Suffix | Example |
|---|---|---|---|
| Aldehydes | Longest chain containing -CHO | -al | CH₃CHO → Ethanal |
| Ketones | Longest chain containing C=O | -one | CH₃COCH₃ → Propan-2-one (Acetone) |
| Carboxylic Acids | Longest chain containing -COOH | -oic acid | CH₃COOH → Ethanoic acid |
| The carbonyl carbon is always numbered as C1 in aldehydes and carboxylic acids. In ketones, the carbonyl carbon gets the lowest possible number. | |||
Common Names — Must Memorise
- Formaldehyde: HCHO (Methanal)
- Acetaldehyde: CH₃CHO (Ethanal)
- Acetone: CH₃COCH₃ (Propan-2-one)
- Formic acid: HCOOH (Methanoic acid)
- Acetic acid: CH₃COOH (Ethanoic acid)
- Benzaldehyde: C₆H₅CHO
- Benzoic acid: C₆H₅COOH
Structure and Bonding of the Carbonyl Group
Key Features
- sp² Hybridisation: The carbonyl carbon is trigonal planar.
- Electrophilic Carbon: The carbon is electron-deficient (δ+) and susceptible to nucleophilic attack.
- Nucleophilic Oxygen: The oxygen is electron-rich (δ-) and can act as a nucleophile.
- Polarity: The C=O bond has a dipole moment (μ ≈ 2.3-2.8 D).
Reactivity Comparison
| Factor | Aldehydes | Ketones |
|---|---|---|
| Steric Hindrance | Less (one alkyl group) | More (two alkyl groups) |
| Electrophilicity | Higher (less electron donation) | Lower (more electron donation) |
| Reactivity towards Nu | More reactive | Less reactive[reference:15] |
| Aldehydes are more reactive than ketones towards nucleophilic addition due to less steric hindrance and greater electrophilicity.[reference:16] | ||
Preparation of Aldehydes and Ketones
| Method | Reaction | Product |
|---|---|---|
| Oxidation of Alcohols | 1° alcohol → aldehyde (PCC, mild oxidising agent) | Aldehyde |
| Oxidation of Alcohols | 2° alcohol → ketone (K₂Cr₂O₇, KMnO₄) | Ketone |
| Ozonolysis of Alkenes | R-CH=CH-R' → R-CHO + R'-CHO | Aldehydes |
| Hydrolysis of Geminal Dihalides | R-CHCl₂ + H₂O → R-CHO | Aldehyde |
| Friedel-Crafts Acylation | Aromatic ring + acyl chloride (AlCl₃) → Aryl ketone | Ketone |
| Grignard Reagent with Nitriles | R-MgX + R'-CN → R-CO-R' (after hydrolysis) | Ketone |
| Aldehydes cannot be prepared by direct oxidation of primary alcohols with strong oxidising agents (they would be further oxidised to carboxylic acids). PCC is used to stop at the aldehyde stage. | ||
Nucleophilic Addition Reactions — The Core Mechanism
General Mechanism
- Step 1: Nucleophile attacks the carbonyl carbon, forming a tetrahedral intermediate.
- Step 2: The tetrahedral intermediate is protonated (or loses a leaving group) to give the final product.
Important Nucleophilic Addition Reactions
| Nucleophile | Reaction | Product |
|---|---|---|
| HCN (CN⁻) | C=O + HCN → | Cyanohydrin (R-CH(OH)-CN) |
| NaHSO₃ | C=O + NaHSO₃ → | Bisulphite adduct |
| NH₃ / RNH₂ | C=O + NH₃ → | Imine (Schiff base) |
| H₂O (Hydration) | C=O + H₂O → | Geminal diol (hydrate) |
| ROH (Acid) | C=O + ROH → | Acetal / Ketal |
| RMgX (Grignard) | C=O + RMgX → | Alcohol |
| LiAlH₄ / NaBH₄ | C=O + [H] → | Alcohol |
| The addition of HCN (cyanohydrin formation) is a very important reaction. It increases the carbon chain length by one carbon. | ||
Named Reactions — Must-Know for JEE and NEET
Named organic reactions are guaranteed marks in JEE and NEET — every paper has at least 2-3 questions on Aldol, Cannizzaro, Wittig, or similar reactions[reference:18].
Aldol Condensation
- Reaction: 2 R-CH₂-CHO → R-CH₂-CH(OH)-CHR-CHO (β-hydroxy aldehyde)
- Conditions: Dilute base (NaOH, Ba(OH)₂) or acid.
- Dehydration: Aldol can be dehydrated to α,β-unsaturated carbonyl compound.
- Examples: Acetaldehyde gives 3-hydroxybutanal (aldol). Acetone gives diacetone alcohol.
Cannizzaro Reaction
- Reaction: 2 R-CHO + NaOH (conc.) → R-CH₂OH + R-COONa
- Conditions: Concentrated NaOH.
- Examples: Formaldehyde (HCHO) gives methanol + sodium formate. Benzaldehyde (C₆H₅CHO) gives benzyl alcohol + sodium benzoate.
- Crossed Cannizzaro: Reaction between two different aldehydes without α-H.
Clemmensen Reduction
- Reaction: R-CO-R' + 4[H] (Zn-Hg/HCl) → R-CH₂-R' + H₂O
- Application: Used to reduce ketones and aldehydes to alkanes.
- Limitation: Not suitable for acid-sensitive compounds.
Wolff-Kishner Reduction
- Reaction: R-CO-R' + NH₂NH₂ (KOH, heat) → R-CH₂-R' + N₂
- Mechanism: Formation of hydrazone, followed by loss of N₂ and protonation.
- Advantage: Works under basic conditions, suitable for acid-sensitive compounds.
Haloform Reaction
- Reaction: R-CO-CH₃ + 3X₂ + 4NaOH → R-COONa + 3NaX + 3H₂O + CHX₃
- Iodoform Test: Yellow precipitate of CHI₃ indicates the presence of a methyl ketone or acetaldehyde.
Hell-Volhard-Zelinsky (HVZ) Reaction
- Reaction: R-CH₂-COOH + Br₂ (red P) → R-CH(Br)-COOH
- Mechanism: Formation of acyl bromide, followed by α-bromination via enolisation.
- Application: Synthesis of α-bromo carboxylic acids.
Carboxylic Acids — Acidity and Reactions
Acidity of Carboxylic Acids
Carboxylic acids are more acidic than alcohols and phenols because the carboxylate ion (R-COO⁻) is stabilised by resonance. The negative charge is delocalised over both oxygen atoms of the carboxylate group.
Electron-withdrawing groups (EWG) increase the acidity of carboxylic acids, while electron-donating groups (EDG) decrease it. For example, CH₃COOH (acetic acid, pKa ≈ 4.76) is more acidic than CH₃CH₂COOH (propionic acid, pKa ≈ 4.87) because the methyl group is electron-donating.
Important Reactions of Carboxylic Acids
| Reaction | Reagent | Product |
|---|---|---|
| Esterification | R-COOH + R'-OH (H⁺) | Ester (R-COO-R')[reference:27] |
| Decarboxylation | R-COOH (heat) | Alkane (R-H) + CO₂ |
| Reduction | LiAlH₄ | Primary alcohol (R-CH₂OH) |
| HVZ Reaction | Br₂ + red P | α-Bromo carboxylic acid[reference:28] |
| Acyl Chloride Formation | SOCl₂ or PCl₅ | Acyl chloride (R-COCl)[reference:29] |
| Esterification is the most important reaction of carboxylic acids. It is reversible and requires acid catalysis. | ||
Practice Questions — From JEE and NEET
| Question | Answer |
|---|---|
| Q1: Which is more reactive towards nucleophilic addition: acetaldehyde or acetone? | Acetaldehyde (less steric hindrance, more electrophilic carbonyl carbon). |
| Q2: What is the product of the aldol condensation of acetaldehyde? | 3-Hydroxybutanal (aldol). On dehydration, gives crotonaldehyde (but-2-enal). |
| Q3: What is the product of the Cannizzaro reaction of benzaldehyde? | Benzyl alcohol (C₆H₅CH₂OH) and sodium benzoate (C₆H₅COONa). |
| Q4: Which reagent is used for the Clemmensen reduction of ketones? | Zn-Hg / conc. HCl. |
| Q5: Which reagent is used for the Wolff-Kishner reduction of ketones? | NH₂NH₂ / KOH (heat). |
| Q6: Why are carboxylic acids more acidic than alcohols? | Due to resonance stabilisation of the carboxylate ion (R-COO⁻). |
| Q7: What is the product of the HVZ reaction of propionic acid (CH₃CH₂COOH)? | 2-Bromopropionic acid (CH₃-CH(Br)-COOH). |
| Q8: What is the IUPAC name of CH₃COCH₂CH₃? | Butan-2-one. |
| Practise these types of questions to become comfortable with applying the concepts of aldehydes, ketones, and carboxylic acids in exam scenarios. | |
All Aldehydes, Ketones and Carboxylic Acids Formulas at a Glance
| Formula/Concept | What It Means |
|---|---|
| R-CHO | General formula for aldehydes |
| R-CO-R' | General formula for ketones |
| R-COOH | General formula for carboxylic acids |
| 2 R-CH₂-CHO → R-CH₂-CH(OH)-CHR-CHO | Aldol condensation (β-hydroxy carbonyl) |
| 2 R-CHO + NaOH → R-CH₂OH + R-COONa | Cannizzaro reaction |
| R-CO-R' + Zn-Hg/HCl → R-CH₂-R' | Clemmensen reduction |
| R-CO-R' + NH₂NH₂/KOH → R-CH₂-R' + N₂ | Wolff-Kishner reduction |
| R-CO-CH₃ + 3X₂ + 4NaOH → R-COONa + CHX₃ + 3NaX + 3H₂O | Haloform reaction |
| R-CH₂-COOH + Br₂ (red P) → R-CH(Br)-COOH | HVZ reaction |
| RCOOH > C₆H₅OH > H₂O > ROH | Acidity order |
| Memorise these formulas for Aldehydes, Ketones and Carboxylic Acids. They are the key to scoring full marks in this chapter. | |
Common Mistakes in Aldehydes, Ketones and Carboxylic Acids
- Confusing aldehydes and ketones in reactions: Aldehydes are more reactive towards nucleophilic addition and give positive Tollens and Fehling's tests (except benzaldehyde). Ketones do not.
- Forgetting the conditions for Cannizzaro reaction: Only aldehydes without α-H undergo Cannizzaro reaction. Aldehydes with α-H undergo aldol condensation.
- Misapplying Clemmensen vs Wolff-Kishner: Clemmensen (Zn-Hg/HCl) is for acid-stable compounds; Wolff-Kishner (NH₂NH₂/KOH) is for base-stable compounds.
- Forgetting the HVZ reaction conditions: HVZ requires red phosphorus and bromine. It is not a simple bromination.
- Confusing the acidity order: Carboxylic acids > Phenols > Water > Alcohols. This order is frequently tested.
- Not checking for α-H in aldol condensation: Aldol condensation requires at least one α-H on the carbonyl compound.
Why Aldehydes, Ketones and Carboxylic Acids Matter for JEE and NEET
- High weightage: This chapter appears in 3-4 questions in every JEE Main, JEE Advanced, and NEET chemistry paper[reference:30].
- Foundation for organic chemistry: Understanding this chapter is essential for understanding many other reactions, including Grignard reactions, esterification, and polymer chemistry.
- Direct scoring: Many questions are direct, especially on named reactions, acidity, and nucleophilic addition.
- Conceptual clarity: This chapter rewards students who understand the mechanisms rather than just memorizing reactions.
Get the Complete Aldehydes, Ketones and Carboxylic Acids PDF for Free
Download the full Aldehydes, Ketones and Carboxylic Acids guide with all concepts, mechanisms, reactions, and practice questions. Perfect for last-minute revision before JEE and NEET.
Download Free PDFMaster Class 12 Chemistry with Competishun
Competishun teaches complete JEE and NEET chemistry with structured lectures, DPPs, PYQs and an All India Test Series.
All taught by faculty with 18 to 25 years of experience.
Pratham
Two-year foundation program that builds strong Class 11 chemistry, physics and maths concepts.
Explore PrathamPrakhar
Class 12 program balancing boards, JEE Main and Advanced preparation together.
Explore PrakharPraveen & Fast Lane
Dropper program for a focused repeat attempt, including the accelerated Fast Lane batch.
Explore PraveenPragyaan
Live interactive batch with real-time classes and mentorship for JEE and NEET.
Explore PragyaanDLP Study Material
Complete printed material with DPPs and PYQs for Class 11, Class 12 and droppers, delivered home.
Explore DLPAll India Test Series
Regular JEE and NEET level tests with detailed analysis to track and improve your rank.
Explore Test SeriesFree Chemistry Lectures on YouTube
Want to see Aldehydes, Ketones and Carboxylic Acids taught step by step with clear mechanism explanations? Competishun's full concept lectures are free on its YouTube channel.
More than 2.2 million+ students follow the channel for free concept lectures, PYQ solutions and exam strategy.
Learn the concepts, then use this Aldehydes, Ketones and Carboxylic Acids guide to revise.
Build Your Chemistry Foundation
Class 11, Class 12 or dropper, explore every Competishun program.
Or start free with full concept lectures on YouTube.
About Competishun
Competishun is an online JEE and NEET coaching platform with programs for Class 11, Class 12 and droppers.
Complete DLP study material and an All India Test Series covering JEE Main, Advanced and NEET.
Taught by faculty with 18 to 25 years of experience.
More than 2.2 million+ students follow the Competishun YouTube channel.
Free JEE and NEET Concept Lectures
Follow Competishun for free Physics, Chemistry and Biology lectures, PYQ solutions and strategy.
Read These Next
Carbocation, carbanion, free radical, carbene, nitrene, benzyne, SN1, SN2, E1, E2 explained in depth.
Expected cutoffs, score vs rank analysis, and category-wise percentiles for JEE Main 2027.
Hybridisation, inductive effect, resonance, hyperconjugation, and aromaticity explained in depth.
Frequently Asked Questions — Aldehydes, Ketones and Carboxylic Acids
Tags
