JEE Main Chemistry · Hydrocarbons PYQ
JEE Main Hydrocarbons PYQ (2002–2026)
Hydrocarbons is a P2 Organic Chemistry chapter — ~4% JEE Main weightage with 1 question per session. Foundation for Organic reactions, introduces key reagents and mechanisms (Markovnikov, anti-Markovnikov, ozonolysis, hydrogenation). Covers alkanes, alkenes, alkynes and aromatic hydrocarbons.
Hydrocarbons PYQs from 2002 to 2026 tagged by sub-topic. Every solution identifies the reagent/condition and product with the underlying mechanism.
Hydrocarbons at a Glance
Try 5 Real Hydrocarbons PYQs
5 real JEE Main questions on Hydrocarbons, straight from past papers. Try them, then check the answer.
- Q1JEE Main 2026 (Online) 24th January Morning Shift
$ \text {Arrange the following alkenes in decreasing order of stability. } $
Choose the correct answer from the options given below:
III $>$ I $>$ II $>$ IV
III $>$ II $>$ I $>$ IV
I $>$ III $>$ II $>$ IV
$\mathrm{I}>\mathrm{III}>\mathrm{IV}>\mathrm{II}$
- Q2JEE Main 2025 (Online) 23rd January Morning Shift
Match the List - I with List - II
List - I
Name reactionList - II
Product obtainable(A) Swarts reaction (I) Ethyl benzene (B) Sandmeyer's reaction (II) Ethyl iodide (C) Wurtz Fittig reaction (III) Cyanobenzene (D) Finkelstein reaction (IV) Ethyl fluoride Choose the correct answer from the options given below:
- A-II, B-III, C-I, D-IV
- A-II, B-I, C-III, D-IV
- A-IV, B-I, C-III, D-II
- A-IV, B-III, C-I, D-II
- Q3JEE Main 2024 (Online) 4th April Evening Shift
In the above chemical reaction sequence "A" and "B" respectively are
- $\mathrm{H}_2 \mathrm{O}, \mathrm{H}^{+}$ and $\mathrm{NaOH}_{(\mathrm{alc})} / \mathrm{I}_2$
- $\mathrm{O}_3, \mathrm{Zn} / \mathrm{H}_2 \mathrm{O}$ and $\mathrm{KMnO}_4$
- $\mathrm{H}_2 \mathrm{O}, \mathrm{H}^{+}$ and $\mathrm{KMnO}_4$
- $\mathrm{O}_3, \mathrm{Zn} / \mathrm{H}_2 \mathrm{O}$ and $\mathrm{NaOH}_{(\mathrm{alc})} / \mathrm{I}_2$
- Q4JEE Main 2023 (Online) 31st January Morning Shift
Choose the correct set of reagents for the following conversion.
trans $\left(\mathrm{Ph}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\right) \rightarrow \operatorname{cis}\left(\mathrm{Ph}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\right)$
- $\mathrm{Br_2,alc\cdot KOH,NaNH_2,H_2}$ Lindlar Catalyst
- $\mathrm{Br_2,aq\cdot KOH,NaNH_2,Na}$ (Liq NH$_3$)
- $\mathrm{Br_2,alc\cdot KOH,NaNH_2,Na}$ (Liq NH$_3$)
- $\mathrm{Br_2,aq\cdot KOH,NaNH_2,H_2}$ Lindlar Catalyst
- Q5JEE Main 2022 (Online) 25th July Evening Shift
Major product of the following reaction is
Practise the full Hydrocarbons set
Every past-paper question of this chapter, with solutions, timing and your accuracy tracked.
Key Sub-Topics & What's Tested
Alkanes (Saturated Hydrocarbons)
General formula CnH2n+2, preparation (Wurtz reaction, Kolbe's electrolysis, decarboxylation), combustion, chlorination via free-radical mechanism.
Alkenes (Unsaturated, Double Bond)
CnH2n, preparation (dehydrohalogenation, dehydration), addition reactions (HBr, H₂O, X₂), Markovnikov rule, anti-Markovnikov with peroxide (Kharasch effect).
Alkynes (Triple Bond)
CnH2n-2, preparation (dehalogenation, Kolbe's from alkynoic acid), addition reactions, acidity of terminal alkynes (pKa ~25), Lindlar's catalyst.
Ozonolysis
Alkenes + O₃ → ozonide → zinc/water → ketone + aldehyde (or acids with oxidative workup). Key tool for alkene structure determination.
Aromatic Hydrocarbons (Benzene)
Aromaticity (Hückel's rule, 4n+2 π electrons), electrophilic aromatic substitution (nitration, sulfonation, halogenation, alkylation, acylation).
Substitution Effects in Benzene
Activating groups (OH, NH₂, OR — ortho/para directing). Deactivating groups (NO₂, COOH, SO₃H — meta directing). Halogens are deactivating but ortho/para directing.
Friedel-Crafts Reactions
Friedel-Crafts alkylation (R-Cl + AlCl₃ → C-alkylation), Friedel-Crafts acylation (RCOCl + AlCl₃ → ketone).
Hydrogenation & Reduction
Ni/Pt/Pd hydrogenation of alkenes and alkynes. Lindlar catalyst (Pd/BaSO₄/quinoline) for cis-alkene. Na/NH₃ for trans-alkene.
Question Type Distribution
| Question Type | Share (approx) | Example Pattern |
|---|---|---|
| Product Prediction (Addition Reactions) | 30% | Predict product when propene reacts with HBr in presence of peroxide (anti-Markovnikov). |
| Electrophilic Aromatic Substitution | 20% | Identify major product when nitrobenzene undergoes further nitration. |
| Markovnikov / Anti-Markovnikov | 15% | Which regiochemistry dominates: HBr addition to 2-methyl-2-butene without peroxide? |
| Ozonolysis Products | 10% | Ozonolysis of cis-2-butene gives which carbonyl products? |
| Friedel-Crafts Product | 10% | Benzene + acetyl chloride + AlCl₃ → acetophenone. Identify mechanism step. |
| Structure Determination | 15% | Compound A (C5H10) decolourises Br₂ water, undergoes ozonolysis to give propanal + ethanal — identify A. |
How to Solve Hydrocarbons PYQs
- 1Markovnikov rule: "H adds to C with more H's." In HX + alkene: more-substituted carbon gets X, less-substituted gets H. Anti-Markovnikov (with peroxide) flips this.
- 2For aromatic substitution, identify directing group first. Activating (OH, NH₂, CH₃) = ortho/para. Deactivating (NO₂, COOH) = meta. Halogens = deactivating + ortho/para.
- 3Hückel's rule for aromaticity. Planar, cyclic, conjugated + 4n+2 π electrons (n = 0, 1, 2, ...). Benzene has 6 π electrons, n = 1.
- 4Friedel-Crafts acylation better than alkylation. Alkylation suffers from rearrangement of carbocation, acylation doesn't (acylium ion is resonance-stabilised). Preferred for clean C-C bond.
- 5Ozonolysis for alkene structure determination. Cleaves C=C into two C=O (aldehyde/ketone). Work backwards from ozonolysis products to deduce original alkene.
Common Mistakes That Cost Marks
- Wrong Markovnikov direction. Markovnikov: H adds to carbon with MORE H's (Markovnikov's original statement). Double-check which carbon is "more substituted".
- Confusing activating/deactivating groups. Alkyl groups (CH₃, C₂H₅) are weakly activating. NO₂ is strongly deactivating. OH is activating. Know the 5-6 common groups cold.
- Using Friedel-Crafts alkylation for primary carbocations. Primary R-Cl + AlCl₃ → R⁺ rearranges to secondary or tertiary. Products can be mixtures — use acylation instead.
- Missing anti-periplanar requirement in E2 elimination. E2 needs H and X on anti-periplanar carbons. Otherwise elimination won't proceed.
- Calling aromaticity just "having a ring". Aromaticity requires planar + cyclic + conjugated + Hückel's rule. Cyclohexane is a ring but NOT aromatic (no π electrons).
Related JEE Main Practice
Frequently asked questions
How many Hydrocarbons PYQs should I solve?
Target 50–70 PYQs across 2010–2026. Foundation chapter for Organic. 30-40 hours of practice builds strong pattern recognition for downstream chapters.
Is Hydrocarbons harder than Aldehydes/Ketones?
Comparable difficulty. Hydrocarbons has more basic mechanism concepts; Aldehydes/Ketones builds on Hydrocarbons with more named reactions. Do Hydrocarbons first.
Do I need to memorise all reagent-product pairs?
Yes — memorise the 15-20 most common reagent/product combinations for alkenes, alkynes and benzene. They appear repeatedly in PYQs.
What's the most-tested Hydrocarbons pattern?
Product prediction in Markovnikov/anti-Markovnikov conditions for alkene + HX reaction. Appears in ~3 PYQs per 10-year window.
Is benzene chemistry tested heavily?
Moderately — 1-2 PYQs per paper on electrophilic aromatic substitution. Know directing effects of at least 8 common substituents.
Does Hydrocarbons connect with GOC?
Yes — stability of carbocations (key GOC concept) determines product in Markovnikov and Friedel-Crafts. Strong GOC fluency → easier Hydrocarbons PYQs.
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