The chemistry class 12 board exams revolve around the concepts that different substances interact in certain conditions to give rise to new substances. No matter whether you study organic chemistry reactions, inorganic chemistry reactions, or reaction mechanisms, mastering the concepts of CBSE Class 12 Chemistry Important Reactions is what it takes to score well in the board exams.
Rather than going through numerous pages of textbooks before exams, a student needs something consolidated. This is where this article comes into use for you as it acts as an ultimate CBSE Class 12 Chemistry Reaction Chart giving you Class 12 Chemistry all reactions along with important named reactions and conversions in each chapter.
With this chart, you can answer all types of questions including direct questions, value-based questions, and organic conversion questions in your CBSE 12th Chemistry exam.
CBSE Class 12 Chemistry Important Reactions: Quick Overview
To make your Class 12 Chemistry revision effective, here is a quick snapshot of what we will cover:
- Chapter-wise important reactions (Electrochemistry to Biomolecules).
- A dedicated list of Class 12 Chemistry Named Reactions.
- Commonly tested reagents and what they do.
- A quick-revision table for last-minute preparation.
- Strategies to solve organic conversion reactions.
Chapter-Wise Important Chemistry Reactions
Here is a curated list of Class 12 Chemistry Important Reactions Chapter Wise, strictly aligned with the latest NCERT syllabus and board exam patterns.
1. Electrochemistry
- Reaction: Electrolysis of aqueous NaCl
- Reagents/Conditions: NaCl solution, Pt electrodes
- Products: Cathode: H₂ gas; Anode: Cl₂ gas; Solution: NaOH
- Board Relevance: Frequently asked in 1-mark or 2-mark questions.
- Reaction: Charging of a Lead Storage Battery
- Reagents/Conditions: Electrical energy passed during charging.
- Products: PbSO₄ converts back to Pb (anode) and PbO₂ (cathode).
2. d- and f-Block Elements
- Reaction: Oxidation of Iodide to Iodine by Dichromate
- Equation: Cr₂O₇²⁻ + 14H⁺ + 6I⁻ → 2Cr³⁺ + 3I₂ + 7H₂O
- Reagent: Acidified K₂Cr₂O₇
- Board Relevance: Important for balancing equations and understanding oxidizing properties.
- Reaction: Potassium Permanganate oxidizing Oxalate ion
- Equation: 2MnO₄⁻ + 5C₂O₄²⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O
- Condition: Warm, acidified with dilute H₂SO₄.
3. Haloalkanes and Haloarenes
- Reaction: Preparation of Alkyl Halides from Alcohols
- Reagents: ROH + PCl₅ / SOCl₂ / HCl (with ZnCl₂)
- Products: R-Cl + byproducts. (SOCl₂ is preferred as byproducts are gaseous).
- Reaction: Hydrolysis of Haloalkanes
- Reagents: Aqueous NaOH / KOH
- Products: Alcohols (Nucleophilic substitution reactions – SN1/SN2).
4. Alcohols, Phenols, and Ethers
- Reaction: Dehydration of Alcohols to Alkenes
- Reagents: Conc. H₂SO₄, 443 K (or 170°C)
- Products: Alkene + H₂O (Elimination reaction).
- Reaction: Preparation of Phenol from Cumene
- Reagents: Cumene + O₂ → Cumene hydroperoxide → Phenol + Acetone (H₃O⁺).
- Board Relevance: Important industrial preparation.
5. Aldehydes, Ketones, and Carboxylic Acids
- Reaction: Oxidation of Tertiary Butyl Alcohol
- Reagents: Acidic K₂Cr₂O₇ or KMnO₄
- Products: No reaction (Tertiary alcohols are resistant to oxidation).
- Reaction: Preparation of Carboxylic Acids from Aldehydes
- Reagents: KMnO₄ / K₂Cr₂O₇ / Tollens’ reagent
- Products: Carboxylic acids.
6. Amines
- Reaction: Basic Nature of Amines
- Reagents: Amine + HCl
- Products: Amine hydrochloride salt (water-soluble).
- Reaction: Acylation of Amines
- Reagents: R-NH₂ + (CH₃CO)₂O / CH₃COCl
- Products: N-substituted amides.
7. Biomolecules
- Reaction: Glucose to Gluconic Acid
- Reagents: Glucose + Br₂ water
- Products: Gluconic acid (Confirms aldehyde group).
- Reaction: Sucrose Hydrolysis
- Reagents: Sucrose + dil. H₂SO₄ / Invertase
- Products: Glucose + Fructose (Invert sugar).
Important Organic Chemistry Reactions
Organic chemistry constitutes a massive portion of the board exam. To master it, you must understand the types of transformations:
- Substitution Reactions: Replacing an atom/group (e.g., Haloalkane to Alcohol using aq. NaOH).
- Elimination Reactions: Loss of atoms to form a double bond (e.g., Alcohol to Alkene using conc. H₂SO₄).
- Oxidation Reactions: Gain of oxygen or loss of hydrogen (e.g., Primary alcohol to Aldehyde/Carboxylic acid).
- Reduction Reactions: Gain of hydrogen or loss of oxygen (e.g., Aldehyde/Ketone to Alcohol using NaBH₄).
- Esterification: Carboxylic acid + Alcohol → Ester (using conc. H₂SO₄ as a catalyst).
Important Named Reactions for CBSE Class 12 Chemistry
Class 12 Chemistry Named Reactions are highly predictable and frequently asked. You must know the exact reagents and conditions.
- Wurtz Reaction: 2R-Br + 2Na (dry ether) → R-R + 2NaBr. (Prepares higher alkanes).
- Finkelstein Reaction: R-Cl + NaI (Acetone) → R-I + NaCl. (Prepares alkyl iodides; NaCl precipitates).
- Swarts Reaction: R-Cl + AgF → R-F + AgCl. (Prepares alkyl fluorides).
- Williamson Ether Synthesis: R-ONa + R’-X → R-O-R’ + NaX. (Prepares unsymmetrical ethers; SN2 mechanism).
- Kolbe’s Reaction: Sodium phenoxide + CO₂ (125 atm, 400K) → Salicylic acid. (Introduces -COOH group ortho to -OH).
- Reimer-Tiemann Reaction: Phenol + CHCl₃ + NaOH → Salicylaldehyde. (Introduces -CHO group ortho/para to -OH).
- Rosenmund Reduction: R-COCl + H₂/Pd-BaSO₄ → R-CHO + HCl. (Reduces acid chloride to aldehyde; Pd-BaSO₄ is the poison/catalyst).
- Stephen Reaction: R-CN + SnCl₂/HCl → R-CH=NH.HCl → R-CHO (on hydrolysis). (Nitrile to aldehyde).
- Aldol Condensation: 2 molecules of R-CH₂-CHO + dil. NaOH → R-CH(OH)-CH(R)-CHO. (Aldehydes/ketones with α-hydrogen).
- Cannizzaro Reaction: 2HCHO + conc. NaOH → CH₃OH + HCOONa. (Aldehydes without α-hydrogen undergo self-disproportionation).
- Clemmensen Reduction: R-CO-R’ + Zn(Hg)/HCl → R-CH₂-R’. (Reduces C=O to CH₂).
- Wolff-Kishner Reduction: R-CO-R’ + NH₂NH₂ + KOH → R-CH₂-R’. (Reduces C=O to CH₂ under basic conditions).
- Hell-Volhard-Zelinsky (HVZ) Reaction: R-CH₂-COOH + Br₂/Red P → R-CH(Br)-COOH. (Brominates at the α-position of carboxylic acids).
- Hoffmann Bromamide Reaction: R-CONH₂ + Br₂ + 4KOH → R-NH₂ + K₂CO₃ + 2KBr + 2H₂O. (Converts amide to primary amine with 1 less carbon atom).
- Gabriel Phthalimide Synthesis: Phthalimide + KOH → Potassium phthalimide → R-NH₂. (Prepares pure primary amines).
- Carbylamine Reaction: R-NH₂ + CHCl₃ + 3KOH (alc.) → R-NC + 3KCl + 3H₂O. (Test for primary amines; produces foul-smelling isocyanides).
- Diazotisation: R-NH₂ + NaNO₂ + HCl (0-5°C) → R-N₂⁺Cl⁻. (Primary aromatic amines to benzene diazonium chloride).
- Sandmeyer Reaction: R-N₂⁺Cl⁻ + CuCl/CuBr/CuCN → R-Cl/R-Br/R-CN. (Replaces diazonium group with halogens or CN).
Important Reagents and Their Uses in Class 12 Chemistry
Knowing what a reagent does is more important than memorizing the whole equation. Here is a quick guide:
| Reagent | What it Does (Transformation) |
|---|---|
| KMnO₄ (Acidic/Alkaline) | Strong oxidizing agent (Alcohol→Acid, Alkene→Diol/Acid). |
| K₂Cr₂O₇ / H⁺ | Oxidizes primary alc. to acid, secondary alc. to ketone. |
| LiAlH₄ (Lithium Aluminium Hydride) | Strong reducing agent (Reduces -COOH, -CN, -COOR to alcohols). |
| NaBH₄ (Sodium Borohydride) | Mild reducing agent (Reduces -CHO and >C=O to alcohols; does not reduce -COOH). |
| PCC (Pyridinium Chlorochromate) | Selective oxidation (Primary alcohol → Aldehyde, stops at aldehyde). |
| H₂ / Ni, Pt, Pd | Catalytic hydrogenation (Alkene→Alkane, -NO₂→-NH₂, -CN→-CH₂NH₂). |
| Br₂ / CCl₄ | Tests unsaturation (Alkene → Vicinal Dibromide, reddish-brown color decolorizes). |
| SOCl₂ (Thionyl Chloride) | Converts -OH to -Cl (byproducts are gaseous, easy purification). |
| PCl₅ / PCl₃ | Converts -OH to -Cl. |
| NaNO₂ + HCl (0-5°C) | Converts primary aromatic amines to diazonium salts. |
| Grignard Reagent (R-MgX) | Nucleophilic addition to >C=O to form alcohols. |
CBSE Class 12 Chemistry Reaction Sheet
Use this table for your Class 12 Chemistry Important Reactions PDF download or to make physical flashcards.
| Reactant | Reagent/Condition | Product | Reaction Name |
|---|---|---|---|
| 2 R-X + 2Na | Dry Ether | R-R (Alkane) | Wurtz Reaction |
| R-X + NaI | Acetone | R-I | Finkelstein Reaction |
| R-ONa + R’-X | Dry Ether | R-O-R’ (Ether) | Williamson Synthesis |
| Phenol + CHCl₃ + NaOH | Heat | Salicylaldehyde | Reimer-Tiemann Reaction |
| Sodium Phenoxide + CO₂ | 125 atm, 400K | Salicylic Acid | Kolbe’s Reaction |
| R-CHO (no α-H) + Conc. NaOH | Heat | Alcohol + Sodium Salt | Cannizzaro Reaction |
| R-COCl + H₂ | Pd-BaSO₄ | R-CHO | Rosenmund Reduction |
| R-CO-R’ | Zn(Hg)/HCl | R-CH₂-R’ | Clemmensen Reduction |
| R-CH₂-COOH + Br₂ | Red Phosphorus | R-CH(Br)-COOH | HVZ Reaction |
| R-CONH₂ + Br₂ + KOH | Heat | R-NH₂ | Hoffmann Bromamide |
| C₆H₅-NH₂ + NaNO₂ + HCl | 273-278 K | C₆H₅-N₂⁺Cl⁻ | Diazotisation |
| C₆H₅-N₂⁺Cl⁻ + CuCN | Warm | C₆H₅-CN | Sandmeyer Reaction |
Top Important Reactions to Memorise for Board Exams
To optimize your time, categorize your CBSE 12th Chemistry Important Reactions into three buckets:
Must Learn (High Weightage)
- Hoffmann Bromamide Reaction
- Gabriel Phthalimide Synthesis
- Aldol Condensation
- Cannizzaro Reaction
- Sandmeyer Reaction
- Diazotisation
Important (Frequently Asked)
- Rosenmund Reduction
- Clemmensen & Wolff-Kishner Reduction
- Reimer-Tiemann & Kolbe’s Reaction
- Williamson Ether Synthesis
- Oxidation of primary/secondary alcohols with K₂Cr₂O₇.
Quick Revision (1-Markers)
- Carbylamine Reaction
- Finkelstein & Swarts Reaction
- Esterification
- Hydrolysis of Esters and Amides
Pro Tip: Prioritize understanding reaction conditions rather than memorizing equations blindly.
Important Organic Conversion Reactions
Organic conversions carry 3-5 marks in the CBSE board exam. You approach them using a backward strategy:
Example: Convert Ethanol to But-2-ene.
- Identify the end goal: But-2-ene is an alkene (requires elimination).
- Identify the starting material: Ethanol has 2 carbons; But-2-ene has 4. (Requires coupling).
- Pathway Formulation:
- Step 1: Ethanol → Ethene (Dehydration using conc. H₂SO₄ at 443K).
- Step 2: Ethene → 1,2-Dibromoethane (Addition of Br₂/CCl₄).
- Step 3: 1,2-Dibromoethane → But-2-ene (Wurtz Reaction using Na/dry ether, followed by dehydrohalogenation OR directly via coupling of vicinal dihalides).
- Alternative Path: Ethanol → Ethanal (Oxidation) → Aldol Condensation (dil. NaOH) → But-2-enal → Reduction → But-2-ene.
How to select the correct reaction:
- Count the number of carbon atoms (to see if you need Wurtz or CN addition).
- Look at the functional group shifts (e.g., -OH to -Cl uses SOCl₂).
- Identify if oxidation (K₂Cr₂O₇) or reduction (LiAlH₄/NaBH₄) is needed.
Common Mistakes Students Should Avoid
- Forgetting reaction conditions: Writing “NaOH” instead of “alc. NaOH” changes a substitution reaction to an elimination reaction.
- Confusing similar reagents: Using KMnO₄ when PCC is required will over-oxidize your alcohol to a carboxylic acid instead of stopping at the aldehyde.
- Writing incorrect products: In Cannizzaro, writing that an alkene is formed instead of an alcohol and a salt.
- Forgetting catalysts: Missing “Anhydrous” conditions for Grignard reagents or Wurtz reaction.
- Mixing up oxidation and reduction: Confusing Clemmensen (reduction) with oxidation reactions.
- Ignoring reaction mechanisms where required: CBSE sometimes asks for the mechanism of Aldol Condensation or SN1/SN2. Do not ignore them.
How to Revise Chemistry Reactions Effectively
- First Revision: Read NCERT thoroughly. Highlight the reagents and conditions.
- Reaction-Sheet Revision: Write down all named reactions on an A4 sheet. Stick it on your study table.
- Practice from NCERT: Solve all in-text and exercise questions. CBSE rarely asks outside NCERT.
- Previous-Year Questions: Solve the last 5 years’ CBSE papers to identify repeatedly asked conversions.
- Sample Papers: Time yourself. Try to write balanced equations in under 1 minute each.
- Final Revision Before Examination: Only look at your CBSE Class 12 Chemistry Reaction Sheet and the reagent table provided above.
Frequently Asked Questions (FAQs)
1. What are the most important reactions in Class 12 Chemistry?
Named reactions like Hoffmann Bromamide, Aldol Condensation, Cannizzaro, Sandmeyer, and Rosenmund Reduction are the most important reactions in Class 12 Chemistry.
2. Which reactions should I learn for the CBSE Class 12 board exam?
You should strictly focus on NCERT reactions, especially organic conversions, named reactions, and the oxidation/reduction reactions of K₂Cr₂O₇ and KMnO₄.
3. Where can I find Class 12 Chemistry Important Reactions PDF?
You can screenshot or print this page to create your own PDF. EducationIdol.in also provides downloadable revision sheets for board exam preparation.
4. What are the important named reactions in Class 12 Chemistry?
There are about 18 named reactions, including Wurtz, Finkelstein, Williamson Synthesis, Reimer-Tiemann, Kolbe’s, Clemmensen, Wolff-Kishner, and Carbylamine reactions.
5. How can I memorize Chemistry reactions quickly?
Do not rote-learn. Understand the mechanism (e.g., nucleophile attacks electrophile). Make flashcards writing only the “Reactant → Reagent → Product” to memorize them quickly.
6. Which organic reactions are important for CBSE Class 12?
Reactions from Aldehydes, Ketones, and Carboxylic Acids (Aldol, Cannizzaro) and Amines (Diazotisation, Sandmeyer, Hoffmann) carry the highest weightage.
7. How should I revise Class 12 Chemistry reactions?
Revise chapter-wise first, then shift to a mixed-reaction sheet. Practice writing the equations physically instead of just reading them.
8. Are NCERT reactions important for the CBSE board exam?
Yes, 100%. CBSE board exams are strictly based on NCERT. If a reaction is in NCERT, it can be asked; if it is not, skip it to save time.
9. What are the most important reagents in Class 12 Chemistry?
LiAlH₄, NaBH₄, PCC, KMnO₄, K₂Cr₂O₇, Grignard Reagent, and CuCN (for Sandmeyer) are the most frequently tested reagents.
10. How can I prepare organic Chemistry reactions for boards?
Start by learning the properties of functional groups. Then, learn how specific reagents react with those groups. Finally, practice 2-3 step conversion questions daily.
Conclusion
CBSE Class 12 Chemistry Important Reactions do not demand you to memorize numerous equations. It demands an intelligent approach towards learning about the functional groups, reagents needed for each reaction, and conditions which help the reaction to proceed further. Using this detailed of Class 12 Chemistry reactions list, along with paying due attention to the named reactions and reagents table above, will allow you to handle even the most challenging organic transformation questions easily.
Remember, the CBSE board tests your conceptual understanding. Make sure your equation is balanced, the conditions are correct, and the products are right.