JEE Main · Chemistry · Organic Chemistry: Some Basic Principles and Techniques
Structural Isomerism: JEE Main previous year questions
15 questions in the 108 JEE Main shifts Lumi analysed, in 5 of 8 years. Pattern: Asked most years. 10 came in 2024–26. Here is how it is asked and which ideas come back.
- Questions
- 15
- in 14 of 108 shifts
- Years asked
- 5/8
- last asked 2026
- Weighted estimate
- 0.2
- model; history: 0.1 a shift on average, typically 0.0–0.3
Key findings
- 01
Asked in 5 of 8 years with analysed shifts and in 14 of 108 shifts: 15 questions, #160 of 196 topics. The years that asked it were 1.2 apart on average.
- 02
60% of its questions since 2020 tested an idea no earlier year had asked; 4 repeated an idea from the year before.
- 03
The most repeated idea is Enumeration of Structural Isomers, asked 5 times in 5 shifts (2021, 2022, 2024, 2026), most often as “count monochloro products of isomers”.
- 04
JEE Main has asked 9 of the 53 ideas in this topic; 37 have never been asked, directly or inside another question.
- 05
Mostly asked as numerical value (40%); 40% need a numerical answer, 20% are easy and 20% hard. It went up from 0.0 to 0.3 questions a shift since 2024.
- 06
The skill tested most is multi-step (33%), then conceptual (33%).
Questions a shift, year by year
Out of the 25 Chemistry questions in a shift. Years differ in how many shifts Lumi analysed, so each year is scaled to one shift.
Raw count: 2017: 0 in 1 shift · 2020: 0 in 12 shifts · 2021: 2 in 24 shifts · 2022: 3 in 24 shifts · 2023: 0 in 12 shifts · 2024: 5 in 18 shifts · 2025: 2 in 8 shifts · 2026: 3 in 9 shifts.
- Up to 2023
- 0.0
- a shift, of 25
- Since 2024
- 0.3
- 0.2
- Usual gap
- 1.2 yrs
- between years asking it
- Shifts with it
- 14/108
- 13% of analysed shifts
How it is asked
Difficulty, format and skill
Across all 15 questions on Structural Isomerism since 2017.
Difficulty
QUESTIONS- Easy3 · 20%
- Medium9 · 60%
- Hard3 · 20%
Format
SHARE- Numerical value · 6 Q40%
- Diagram based · 3 Q20%
- Single correct · 2 Q13%
- Other · 2 Q13%
- Two statements · 1 Q7%
- Match the list · 1 Q7%
Skill tested
SHARE- Multi-step · 5 Q33%
- Conceptual · 5 Q33%
- Application · 2 Q13%
- Recall · 2 Q13%
- Diagram reading · 1 Q7%
Repeats
New idea, or one asked before?
Each column is a year. Blue questions tested an idea no earlier year had asked; navy ones went back to an idea from an earlier year. 2017 is the first year, so everything in it counts as new. Heights are question counts, and Lumi analysed 1 to 24 shifts a year, so compare the split inside a column rather than heights across years.
- Idea asked for the first time
- Idea asked in an earlier year
Coverage of the topic
JEE Main has asked 9 of the 53 ideas in this topic. 37 have never been asked yet.
- Asked directly9 · 17%
- Touched inside another question7 · 13%
- Never asked37 · 70%
Ideas come from Lumi’s JEE syllabus map. A never-asked idea is not a safe skip: across all of JEE Main, 22% of questions since 2024 tested an idea no earlier year had asked.
Drill down
Chapter, idea, question
Every idea JEE Main tested in this topic, with its eight years. Open one to read the questions.
6 ideas inside
Squares are the 8 years with analysed shifts, 2017 to 2026. A number is the questions that year when there is more than one; the shade is scaled to one shift, so a year with more analysed shifts (1 to 24 a year) does not look darker. Share is of the level above.
Ideas
Every idea inside this topic
9 different ideas were tested; 2 came more than once.
count monochloro products of isomers
Numerical value · 5 shifts · 5 numericalstatement i/ii on metamerism and tautomerism
Diagram based · 3 shiftsidentify hydrocarbon from molar mass and carbon types
Single correct · 1 shiftcount structural isomers of formula
Numerical value · 1 shift · 1 numericalcompare enol content of cyclic polyketones
Diagram based · 1 shiftidentify b and c and relation between a and c
Other · 1 shiftmatch compound pairs with isomerism type
Match the list · 1 shiftcompare enol content of diketones
Diagram based · 1 shiftidentify isomerism type of formula
Single correct · 1 shift
| Idea | Years asked | Times | Shifts | Format | Numerical |
|---|---|---|---|---|---|
| Enumeration of Structural Isomerscount monochloro products of isomers | 5 | 5 | Numerical valueMulti-step | 5 | |
| Metamerismstatement i/ii on metamerism and tautomerism | 3 | 3 | Diagram basedConceptual | – | |
| Chain Isomerismidentify hydrocarbon from molar mass and carbon types | 1 | 1 | Single correctApplication | – | |
| Isomer Counting in Benzene Derivativescount structural isomers of formula | 1 | 1 | Numerical valueApplication | 1 | |
| Aromaticity-Driven Enolizationcompare enol content of cyclic polyketones | 1 | 1 | Diagram basedConceptual | – | |
| Chain vs Position Priority Resolutionidentify b and c and relation between a and c | 1 | 1 | OtherMulti-step | – | |
| Position Isomerismmatch compound pairs with isomerism type | 1 | 1 | Match the listRecall | – | |
| Enol Content Stability Factorscompare enol content of diketones | 1 | 1 | Diagram basedConceptual | – | |
| Functional Isomerismidentify isomerism type of formula | 1 | 1 | Single correctConceptual | – |
Times and shifts count every analysed shift. Across JEE Main, 78% of questions since 2024 went back to an idea an earlier year had asked; the rest were new. All repeated ideas
Every question
Structural Isomerism questions, year by year
The opening words of each question as it appeared in the official paper, with the idea it tested. Open one for its options and the official answer.
JEE Main 20263 questions in 3 shifts
- 2 Apr, Shift 1Q72Consider the isomers of hydrocarbon with molecular formula . These isomers do not decolourise …
Idea: Enumeration of Structural Isomers
HardNumerical value - 5 Apr, Shift 2Q64Identify the correct IUPAC name of hydrocarbon () containing three primary carbon atoms and with molar mass 72 g mol.
Idea: Chain Isomerism
New ideaEasySingle correct - 6 Apr, Shift 1Q64Given below are two statements: Statement I: 2,6-diethylcyclohexanone and 6-methyl-2-n-propylcyclohexanone are metamers. Statement II:…
Idea: Metamerism
Asked the year beforeMediumTwo statements
JEE Main 20252 questions in 2 shifts
- 3 Apr, Shift 1Q64Identify the correct statements from the following. A. [structure: pentan-3-one (skeletal, C=O at the middle carbon)] and [structure:…
Idea: Metamerism
Asked the year beforeMediumOther · figure - 3 Apr, Shift 2Q75The total number of structural isomers possible for the substituted benzene derivatives with the molecular formula is…
Idea: Isomer Counting in Benzene Derivatives
New ideaMediumNumerical value
JEE Main 20245 questions in 4 shifts
- 4 Apr, Shift 1Q76Identify (B) and (C) and how are (A) and (C) related ? (A) = 1-bromo-4-(2-bromoethyl)benzene drawn as 4-Br-C6H4-CH2CH2Br;…
Idea: Chain vs Position Priority Resolution
New ideaMediumOther · figure - 4 Apr, Shift 1Q88The number of different chain isomers for is ________.
Idea: Enumeration of Structural Isomers
MediumNumerical value - 5 Apr, Shift 2Q74Match List - I with List - II. List - I (Pair of Compounds) List - II (Isomerism) (A) n-propanol and Isopropanol (I) Metamerism (B)…
Idea: Position Isomerism
New ideaEasyMatch the list - 6 Apr, Shift 1Q74Which of the following is metamer of the given compound (X)?
Idea: Metamerism
New ideaMediumDiagram based · figure - 27 Jan, Shift 1Q76Highest enol content will be shown by :
Idea: Aromaticity-Driven Enolization
New ideaHardDiagram based · figure
JEE Main 20223 questions in 3 shifts
- 25 Jul, Shift 2Q90The total number of monobromo derivatives formed by the alkanes with molecular formula is (excluding stereo isomers)…
Idea: Enumeration of Structural Isomers
Asked the year beforeMediumNumerical value - 30 Jul, Shift 2Q59The number of isomeric compounds (structural isomers only) possible with the molecular formula , which do not react…
Idea: Enumeration of Structural Isomers
Asked the year beforeHardNumerical value - 26 Jun, Shift 1Q76Which will have the highest enol content ?
Idea: Enol Content Stability Factors
New ideaMediumDiagram based · figure
JEE Main 20212 questions in 2 shifts
- 22 Jul, Shift 2Q59The number of acyclic structural isomers (including geometrical isomers) for pentene are ________.
Idea: Enumeration of Structural Isomers
New ideaMediumNumerical value - 18 Mar, Shift 1Q42Compound with molecular formula can show :
Idea: Functional Isomerism
New ideaEasySingle correct
Questions from the official JEE Main Paper 1 shifts published by NTA (CBSE for 2017). Questions NTA dropped are left out. Topic and idea tags, counts and notes are Lumi’s.