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Hydrocarbons and Environmental Chemistry – JEE Main Formula Sheet & Class 12 Notes
This is the complete JEE Main Formula Sheet and Class 12 Formula Sheet for Hydrocarbons and Environmental Chemistry — Chapter 12 from the Aakash Rapid Revision & Formula Bank. It covers everything from the preparation and properties of Alkanes, Alkenes, and Alkynes to Aromatic Hydrocarbons including benzene's EAS reactions, and closes with a focused section on Environmental Chemistry — air pollution, water pollution, acid rain, smog, and soil pollution. These topics consistently contribute 4–6 questions in JEE Main every year and are equally important for CBSE Class 12 board exams. Download the free PDF below to keep all key reactions, rules, and concepts within reach during revision.
Topics Covered in This Formula Sheet
JEE Main Formula Sheet PDF Preview
Scroll to explore all Hydrocarbons and Environmental Chemistry formulas — JEE Main & Class 12 Formula Sheet
Introduction: Why This Chapter Matters for JEE Main and Class 12
Chemistry, at its heart, is the study of what things are made of and how they behave. And when it comes to organic chemistry, hydrocarbons are the starting point — literally. They are the simplest organic molecules, built only from carbon and hydrogen, yet they form the backbone of an enormous range of chemical reactions that appear in both competitive exams and everyday science.
For any student preparing for JEE Main, Chapter 12 — Hydrocarbons and Environmental Chemistry — is one of the most reaction-heavy and formula-rich chapters in the entire Class 12 syllabus. The chapter builds on the organic chemistry fundamentals covered in Chapter 11 and takes you into the actual chemical behaviour of carbon compounds: how they are made, how they react, and how some of them end up causing environmental damage.
What makes this chapter stand apart is its dual nature. The first half focuses on pure organic chemistry — the reactions of alkanes, alkenes, alkynes, and aromatic hydrocarbons. The second half shifts to environmental chemistry, where concepts like acid rain, smog, BOD, and COD come in — topics that are increasingly important not just for JEE Main but also for NEET and CBSE boards. Download the Free PDF at the top of this page to have all key concepts in one place.
Overview of Hydrocarbons and Environmental Chemistry
At its core, this chapter answers a simple question: what happens when carbon atoms bond with each other and with hydrogen? Depending on the type of bonds — single, double, or triple — you get alkanes, alkenes, or alkynes respectively. Each class has a distinct set of chemical properties, a distinct set of reactions, and a distinct role in both industry and nature.
Alkanes, the fully saturated hydrocarbons, are relatively unreactive but serve as fuel and industrial starting materials. Alkenes, with their carbon-carbon double bond, are far more reactive and are central to addition reactions tested repeatedly in JEE Main. Alkynes, with their triple bond, bring in unique acidic character and specific reaction patterns. Then there are aromatic hydrocarbons like benzene, which follow their own rulebook — resisting addition and favouring substitution to preserve their stable aromatic ring.
The environmental chemistry section grounds this organic knowledge in real-world problems. Students learn how pollutants enter air, water, and soil — and how chemistry can measure and explain these effects. This makes the chapter practically relevant, not just exam-relevant. Download the Free PDF to access a ready-made revision resource covering all of the above.
Key Concepts Covered in This Chapter
Alkanes — Preparation, Properties, and Reactions
Why Alkanes Are Important for JEE Main
Alkanes form the foundation of hydrocarbon chemistry. In this section, students learn the major synthetic routes — Wurtz Reaction, Corey-House Synthesis, Kolbe's Electrolytic Decarboxylation, Sabatier-Senderen's Reduction, and decarboxylation using soda lime. Each method has specific conditions, limitations, and products that are frequently tested in JEE Main as single-answer or multi-correct MCQs.
Physical properties like boiling point trends, melting point alternation (the ALTERATION EFFECT), and solubility in non-polar solvents are quick one-liners that can earn marks. The chemical reactions — halogenation, nitration, oxidation, isomerization, aromatization — come with specific reagents and conditions that must be memorised precisely. One easily overlooked but exam-favourite topic here is conformational analysis. The staggered and eclipsed conformations of ethane, propane, and butane — shown using Newman and Sawhorse projections — and the stability order (Staggered > Gauche > Eclipsed) are the kind of conceptual details that separate a 95-percentile student from a 99-percentile student in JEE Main.
Alkenes — Preparation, Addition Reactions, and Stereochemistry
Why Alkenes Are Important for JEE Main
Alkenes are the most reaction-rich section of this chapter and consistently account for multiple questions in JEE Main. The preparation methods — dehydration of alcohols (following Saytzeff's Rule), dehydrohalogenation, dehalogenation of vicinal dihalides, Hofmann elimination, catalytic hydrogenation of alkynes using Lindlar's catalyst (cis product) or Na/liq. NH₃ (trans product) — each involve specific stereo or regio-selectivity that is directly tested.
Among the reactions, addition reactions are the most important. Markovnikoff's Rule (the more substituted carbon gets the hydrogen) governs acid-catalysed additions and hydration. The Kharasch-Mayo Effect (anti-Markovnikoff) applies only with HBr in the presence of peroxides. Oxy-mercuration-demercuration gives Markovnikoff's product without rearrangement, while hydroboration-oxidation gives the anti-Markovnikoff product via a syn-addition mechanism.
Ozonolysis, Baeyer's reagent (cold dilute KMnO₄) for syn-dihydroxylation, hot KMnO₄ or acidic KMnO₄ for oxidative cleavage, and addition of carbenes are all potential JEE Main questions. Download the Free PDF to keep a clean summary of all these reaction conditions alongside product predictions.
Alkynes — Preparation, Reactions, and Acidic Character
Why Alkynes Are Important for JEE Main
Alkynes are prepared from dehydrohalogenation of vicinal and geminal dihalides, dehalogenation reactions with Zn dust, Kolbe's electrolysis of maleic/fumaric acid salts, and chain extension using sodamide. Electrophilic addition is the primary reaction, and in the presence of heavy metal salts, nucleophilic addition also occurs (an important exception that JEE Main often tests).
The acidic nature of terminal alkynes is a conceptual highlight. Terminal alkynes (HC≡C–) react with sodium metal, NaNH₂, Tollen's reagent (giving white silver acetylide precipitate), and ammoniacal cuprous chloride (giving red copper acetylide precipitate). These are used as distinguishing tests between terminal and internal alkynes — a classic JEE Main question type.
Kucherov reaction (hydration of alkynes using H⁺/Hg²⁺) gives Markovnikoff's product, typically a ketone, via an enol intermediate. Polymerization of acetylene through a red-hot Cu tube gives benzene — a direct connection to the next section. Download the Free PDF to see all alkyne reaction pathways laid out clearly.
Aromatic Hydrocarbons — Benzene, Aromaticity, and EAS Reactions
Why Aromatic Hydrocarbons Are Important for JEE Main
Aromatic hydrocarbons, especially benzene, bring in one of the most concept-dense topics in Class 12 chemistry. Huckel's Rule — a compound is aromatic if it is cyclic, conjugated, planar, and contains (4n + 2) π electrons — forms the basis of all aromaticity questions in JEE Main. Students must be able to classify species as aromatic, antiaromatic, or non-aromatic based on electron count and geometry. Note: cyclooctatetraene is non-aromatic (not antiaromatic) because it is non-planar.
Electrophilic Aromatic Substitution (EAS) covers halogenation (with FeCl₃ or AlCl₃ as Lewis acid catalysts), nitration (with mixed acid — conc. HNO₃ + conc. H₂SO₄), sulphonation (a reversible reaction), and Friedel-Crafts alkylation and acylation. The directing effect of substituents — ortho/para directors (electron-donating groups like –OH, –NH₂, –alkyl) vs. meta directors (electron-withdrawing groups like –NO₂, –CHO, –COOH, –CN) — is directly tested in 2–3 questions every JEE Main paper.
Friedel-Crafts alkylation proceeds via a carbocation intermediate (subject to rearrangement), while acylation uses an acylium ion (no rearrangement) — a distinction JEE Main tests with predictable regularity. Download the Free PDF for a complete table of activating/deactivating groups with their directing effects.
Environmental Chemistry — Pollutants, Smog, Acid Rain, and Soil Pollution
Why Environmental Chemistry Is Important for JEE Main and NEET
The environmental chemistry section of this chapter is often underestimated, yet it consistently appears in JEE Main. The section opens with a clear definition: any substance that causes pollution is an environmental pollutant. Pollution is classified into atmospheric (air), water, and soil pollution — and each has specific chemical causes, effects, and parameters that are examinable.
Water pollution covers heavy metals (Cd, Pb, Hg), detergents and fertilisers containing phosphates (causing eutrophication), acid-polluted water (pH < 3), and polychlorinated biphenyls (PCBs). The two key measurement tools — Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) — are definitions that come up almost every year. BOD measures oxygen needed by microbes to biologically oxidise organic matter in water; higher BOD means more pollution. COD uses an oxidising agent (K₂Cr₂O₇) to oxidise even materials resistant to microbial action.
Air pollution introduces two types of smog — classical smog (cool, humid, reducing, high SO₂) and photochemical smog (warm, dry, oxidising, major component NO). Acid rain forms when SO₂ and NO₂ react with atmospheric water, dropping rain pH below 5.6. The reactions forming H₂SO₄ and HNO₃ from these oxides are the kind of balanced equations that appear in JEE Main as one-mark direct questions. Download the Free PDF to have all environmental chemistry facts in one structured reference.
The section ends with soil pollution from pesticides and the Bhopal Gas Tragedy (December 2, 1984), caused by the leakage of methyl isocyanate (MIC) from Union Carbide Ltd. The hydrolysis and polymerisation reactions of MIC — both exothermic — explain why the situation escalated so rapidly. This is a factual area that CBSE Class 12 boards often include as a short-answer question.
Download Free PDF — Hydrocarbons & Environmental Chemistry Formula Sheet
All the reactions, rules, conformational diagrams, and environmental chemistry facts from this chapter are compiled into the Aakash Rapid Revision & Formula Bank PDF. It is specifically structured for last-minute revision before JEE Main, CBSE boards, and NEET — covering every subtopic with precision and no filler.
Why This Chapter Is Important for Students and Exams
There are four reasons why every serious JEE Main aspirant and Class 12 student must give this chapter focused attention.
Conceptual clarity across organic chemistry. The reactions taught here — addition, substitution, elimination, oxidation — appear again and again in subsequent chapters on haloalkanes, alcohols, aldehydes, and amines. If a student builds a solid understanding of Markovnikoff's Rule here, it stays relevant for the rest of organic chemistry. Similarly, understanding directing effects in benzene makes aromatic amines and phenols much easier later.
High numerical problem density. Unlike some chapters that are purely factual, Hydrocarbons involves product prediction problems, mechanism-based questions, and comparison questions (which is more stable? which reaction gives the major product?) that require applied thinking. The JEE Main paper regularly features 3–5 questions from this chapter, and these are answerable with smart preparation rather than pure memorisation.
Competitive exam relevance across boards. This chapter is tested in JEE Main, NEET, BITSAT, WBJEE, MHT-CET, and CBSE Class 12 boards. Unlike some niche organic chapters, Hydrocarbons has broad overlap across all major exams. Investing time here earns returns across multiple tests.
Environmental chemistry is a quick scoring zone. The second half of the chapter — environmental pollutants, BOD, COD, smog, acid rain — is factual, finite, and entirely predictable. Students who cover this section thoroughly can score full marks on those questions in every exam, including JEE Main. Download the Free PDF to revise these facts in under 30 minutes before any exam.
Who Should Use This Formula Sheet?
Learning Outcomes After Completing This Chapter
After working through the concepts in this chapter — using the formula sheet and the notes above — a student should be able to do the following with confidence.
For alkanes: predict the product of any preparation method, explain why certain methods fail (e.g., Wurtz fails for methane and 3° alkyl halides), draw Newman and Sawhorse projections for ethane and butane, and state the correct stability order of conformers.
For alkenes: apply Saytzeff's Rule to predict the major elimination product, use Markovnikoff's Rule and its peroxide exception correctly, predict stereo outcomes (cis vs. trans, syn vs. anti) for each addition reaction, and distinguish between reactions that involve carbocation intermediates (with rearrangement risk) and those that do not (like hydroboration).
For alkynes: carry out preparation from geminal and vicinal dihalides, identify a terminal alkyne using Tollen's reagent or cuprous chloride solution, apply Kucherov reaction correctly, and understand why terminal alkynes are acidic.
For aromatic hydrocarbons: apply Huckel's Rule to identify aromaticity, predict EAS products and their positions using directing effects, and distinguish between Friedel-Crafts alkylation and acylation outcomes. Download the Free PDF to test yourself against a curated set of reaction prediction challenges.
For environmental chemistry: define BOD and COD and explain what each measures, classify smog types by their chemistry and climate conditions, write and interpret the acid rain formation reactions, and recall the key facts about the Bhopal Gas Tragedy including the chemistry of MIC.
Get the Free PDF for Quick Revision
Whether you are preparing for JEE Main, CBSE Class 12 boards, or any other engineering or medical entrance exam, having a compact, well-organised formula sheet for this chapter is essential. The Aakash Rapid Revision & Formula Bank PDF for Hydrocarbons and Environmental Chemistry covers every reaction, every rule, every reagent condition, and every environmental chemistry fact you need — in a layout designed for exam-day recall, not passive reading.
Conclusion — Learn the Chemistry, Not Just the Reactions
Hydrocarbons and Environmental Chemistry is not a chapter you can get through by memorising a list of reactions. The best students approach it differently — they understand why Markovnikoff's Rule works (carbocation stability), why Lindlar's catalyst gives a cis product (surface adsorption), and why benzene prefers substitution over addition (preservation of aromaticity). When you understand the reasoning, you stop forgetting the details.
The environmental chemistry section reinforces this point even more directly. Acid rain is not just a fact to memorise — it is a chain of chemical logic: fossil fuel combustion releases SO₂ and NO₂, these oxides react with atmospheric water, and the resulting acids lower rain pH below 5.6. Understanding the chemistry makes the facts stick naturally.
Use this page, the subtopic breakdowns, and the Free PDF Download as your revision foundation. Then go back to your textbook and solved papers to practise applying these concepts under exam conditions. That combination — conceptual clarity plus exam practice — is what translates chemistry knowledge into marks in JEE Main and Class 12 boards.
JEE Main Formula Hub — Chapter-Wise Formulas (Chemistry | Physics | Maths)
Access chapter-wise formula sheets for all three JEE Main subjects. Click on any chapter below to get complete formulas, key concepts, and free PDF downloads prepared from the Aakash Rapid Revision Formula Bank.
Frequently Asked Questions
What is the Wurtz reaction and why does it fail for methane and 3°-alkyl halides?
The Wurtz reaction joins two alkyl halides using sodium metal in dry ether to form a higher alkane: 2R–X + 2Na → R–R + 2NaX. Methane cannot be prepared because it requires a CH₃ group, and the reaction works best with primary alkyl halides. With 3°-alkyl halides, the reaction fails because elimination is favoured over coupling, producing alkenes as side products instead of the desired alkane.
What is Markovnikoff's Rule and when does anti-Markovnikoff addition occur?
Markovnikoff's Rule states that in the addition of a protic acid HX to an unsymmetrical alkene, the hydrogen attaches to the carbon that already has more hydrogen atoms (the less substituted carbon), and X goes to the more substituted carbon. This is because the more substituted carbocation intermediate is more stable. Anti-Markovnikoff addition (Kharasch-Mayo effect) occurs only when HBr is added in the presence of peroxides — the reaction follows a free radical mechanism and the bromine ends up on the less substituted carbon. This exception applies only to HBr; HF, HCl, and HI do not show the peroxide effect.
What is the difference between Lindlar's catalyst and Na/liquid NH₃ in alkyne reduction?
Both reagents partially reduce an alkyne to an alkene, but they give opposite stereochemical outcomes. Lindlar's catalyst (Pd on BaSO₄ or CaCO₃, poisoned with quinoline) causes syn-addition of hydrogen, giving a cis-alkene. Na or Li in liquid ammonia causes anti-addition, giving a trans-alkene. In JEE Main, questions frequently ask which reagent to use when a specific stereoisomer of an alkene is required from an alkyne starting material.
How do you identify a terminal alkyne in the lab, and why are terminal alkynes acidic?
Terminal alkynes (those with a C≡C–H group) can be identified using two tests. With Tollen's reagent (ammoniacal AgNO₃ solution), a white precipitate of silver acetylide forms. With ammoniacal cuprous chloride solution (Cu₂Cl₂/NH₄OH), a red precipitate of copper acetylide forms. Internal alkynes do not give these reactions. Terminal alkynes are acidic because the carbon in the C–H bond is sp hybridised (50% s-character), making it more electronegative and better able to stabilise the negative charge of the conjugate base (acetylide anion) after losing H⁺.
What is Huckel's Rule and how do you use it to identify aromatic compounds?
Huckel's Rule states that a compound is aromatic if it is cyclic, fully conjugated, planar, and contains (4n + 2) π electrons, where n is a non-negative integer (0, 1, 2, 3…). For n = 0, the count is 2; for n = 1, it is 6; for n = 2, it is 10; and so on. Benzene with 6 π electrons (n = 1) is aromatic. If a cyclic conjugated planar compound has 4n π electrons, it is antiaromatic (less stable than an acyclic version). If it lacks planarity or full conjugation, it is simply non-aromatic. Cyclooctatetraene, despite having 8 π electrons, is non-aromatic because it is tub-shaped and non-planar.
What is the difference between Friedel-Crafts alkylation and acylation of benzene?
Both are electrophilic aromatic substitution reactions catalysed by anhydrous AlCl₃. In alkylation, an alkyl halide reacts with benzene to introduce an alkyl group — but the reactive intermediate is a carbocation, which can undergo rearrangement to give unexpected products. In acylation, an acyl halide (like CH₃COCl) reacts with benzene to introduce an acyl group — the reactive intermediate is a resonance-stabilised acylium ion (R–C≡O⁺), which cannot rearrange. So acylation always gives a clean, predictable product, making it the preferred route when a pure compound is needed. This distinction is a JEE Main favourite.
What is BOD and how is it used to measure water pollution?
BOD stands for Biological Oxygen Demand. It is the amount of dissolved oxygen required by microorganisms to biologically oxidise the organic matter present in a given volume of water, measured over at least 5 days. A higher BOD value indicates more organic pollution in the water. BOD is a practical and widely used indicator of water quality because it directly reflects the load of biodegradable organic material. Clean water has very low BOD, while heavily polluted water — such as sewage or industrial effluent — has very high BOD. COD (Chemical Oxygen Demand), measured using K₂Cr₂O₇, captures pollutants that microbes cannot oxidise, giving a broader picture of total water contamination.
What causes acid rain, and what is the normal pH of rain water?
Normal rain water is slightly acidic with a pH of about 5.6, because atmospheric CO₂ dissolves in it to form a weak carbonic acid solution. Acid rain occurs when the pH drops below 5.6 due to the presence of oxides of sulphur and nitrogen in the atmosphere. SO₂ and NO₂ — released primarily from fossil fuel combustion, industrial processes, and vehicle exhausts — react with atmospheric moisture to form sulphuric acid (H₂SO₄) and nitric acid (HNO₃). These strong acids fall with rain and damage vegetation, aquatic life, buildings, statues, and soil. They also leach heavy metals like Cu, Pb, Hg, and Al from soil into groundwater.
What is the difference between classical smog and photochemical smog?
Classical smog (also called London smog) occurs in cool, humid climates. It is a mixture of smoke and fog and is chemically a reducing smog with a high concentration of SO₂. Photochemical smog (Los Angeles smog) occurs in warm, dry, and sunny climates. It is an oxidising smog, and its major component is NO (nitric oxide). Ozone, PAN (peroxyacetyl nitrate), and other secondary pollutants form through photochemical reactions of NO and unburnt hydrocarbons. Photochemical smog causes eye and throat irritation, damages vegetation, and accelerates rubber cracking.
What happened in the Bhopal Gas Tragedy and what is the chemistry behind it?
The Bhopal Gas Tragedy occurred on the night of December 2, 1984, at the Union Carbide plant in Bhopal, India. Methyl isocyanate (MIC, CH₃–N=C=O) — a toxic intermediate used to manufacture the pesticide Carbyl (Sevin) — leaked from one of three storage tanks due to a pressure increase. Two reactions made the situation catastrophic: MIC hydrolysed with water in surrounding ponds to release methylamine gas and CO₂ (exothermic), and MIC polymerised in the presence of metal impurities in the water (also exothermic). Both reactions are highly exothermic, which increased the escaping tendency of MIC and caused massive loss of human life and livestock.
What are ozonolysis and hydroboration oxidation, and what products do they give?
Ozonolysis involves treating an alkene with ozone (O₃) in CCl₄ to form a molozonide, which rearranges to an ozonide. The ozonide is then cleaved with Zn/H₂O (reductive workup) to give aldehydes and ketones depending on the substitution pattern of the alkene. It is used to identify alkene structure by working backwards from the carbonyl products. Hydroboration oxidation involves treating an alkene with diborane (B₂H₆) followed by H₂O₂/OH⁻. The boron adds to the less substituted carbon (anti-Markovnikoff) via syn-addition, and after oxidation, the hydroxyl group ends up on the less substituted carbon. No rearrangement occurs in this reaction — a key feature that distinguishes it from acid-catalysed hydration in JEE Main questions.
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