Organic Chemistry - Some Basic Principles and Techniques Previous Year Questions — JEE Main Chemistry
101 past-year Organic Chemistry - Some Basic Principles and Techniques questions from JEE Main (Chemistry) — page 17.
Q62 (2026)
From the following, the least stable structure is :
- $\text{Option 1}$
- $\text{Option 2}$
- $\text{Option 3}$
- $\text{Option 4}$
### Core Logic
In structure 3, there are positive formal charges on two adjacent atoms (Oxygen and the Carbon adjacent to it). Like charges on adjacent atoms cause extreme electrostatic repulsion, making the structure highly unstable.
{{SOL_IMG1}}
### Pattern Recognition
Rules of resonance stability:
1. Complete octets are more stable.
2. More covalent bonds = more stable.
3. Least charge separation is more stable.
4. Like charges on adjacent atoms create massive destabilization (Least stable scenario).
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Chemistry: Organic Chemistry - Some Basic Principles and Techniques
Q66 (2026)
Identify correct statement from the following:
A. Propanal and propanone are functional isomers.
B. Ethoxyethane and methoxypropane are metamers.
C. But-2-ene shows optical isomerism.
D. But-1-ene and but-2-ene are functional isomers.
E. Pentane and 2, 2-dimethyl propane are chain isomers.
Choose the correct answer from the options given below:
- $\text{B, C and D only}$
- $\text{A, B and C only}$
- $\text{A, B and E only}$
- $\text{C, D and E only}$
### Core Logic
A. Propanal ($CH_3CH_2CHO$) and propanone ($CH_3COCH_3$) have different functional groups (aldehyde vs ketone) but the same molecular formula. They are functional isomers. (Correct)
B. Ethoxyethane ($C_2H_5-O-C_2H_5$) and methoxypropane ($CH_3-O-C_3H_7$) differ in the alkyl chains attached to the polyvalent oxygen atom. They are metamers. (Correct)
C. But-2-ene shows geometrical isomerism (cis-trans), but no optical isomerism as it lacks a chiral center. (Incorrect)
D. But-1-ene and but-2-ene differ in the position of the double bond. They are position isomers, not functional isomers. (Incorrect)
E. Pentane (straight chain) and 2,2-dimethyl propane (branched chain) have the same formula $C_5H_{12}$ but different carbon skeletons. They are chain isomers. (Correct)
Correct statements: A, B, and E.
### Pattern Recognition
Metamerism arises when there is a difference in the alkyl groups attached to a polyvalent functional group (e.g., -O-, -S-, -NH-, -CO-).
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Chemistry: Organic Chemistry - Some Basic Principles and Techniques
Q52 (2026)
Match List-I with List-II.
<div style="overflow-x: auto; margin: 1rem 0;"><table style="width: 100%; border-collapse: collapse; text-align: left; font-size: 14px;"><thead><tr><th style="border: 1px solid #888; padding: 8px;">List-I (Pair of Compounds)</th><th style="border: 1px solid #888; padding: 8px;">List-II (Type of Isomers)</th></tr></thead><tbody><tr><td style="border: 1px solid #888; padding: 8px;">A. 2-Methylpropene and but-1-ene</td><td style="border: 1px solid #888; padding: 8px;">I. Stereoisomers</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">B. Cis-but-2-ene and trans-but-2-ene</td><td style="border: 1px solid #888; padding: 8px;">II. Position isomers</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">C. 2-Butanol and diethyl ether</td><td style="border: 1px solid #888; padding: 8px;">III. Chain isomers</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">D. But-1-ene and but-2-ene</td><td style="border: 1px solid #888; padding: 8px;">IV. Functional group isomers</td></tr></tbody></table></div>
Choose the correct answer from the options given below:
- $(1) \ A-\text{III}, B-\text{I}, C-\text{IV}, D-\text{II}$
- $(2) \ A-\text{III}, B-\text{I}, C-\text{II}, D-\text{IV}$
- $(3) \ A-\text{I}, B-\text{IV}, C-\text{III}, D-\text{II}$
- $(4) \ A-\text{II}, B-\text{I}, C-\text{IV}, D-\text{III}$
### Core Logic
- A. 2-Methylpropene and but-1-ene differ in carbon chain structure $\rightarrow$ III. Chain isomers
- B. Cis-but-2-ene and trans-but-2-ene differ in spatial arrangement $\rightarrow$ I. Stereoisomers
- C. 2-Butanol (alcohol) and diethyl ether (ether) have different functional groups $\rightarrow$ II. Functional isomers (Note: matches with II/IV based on pairing context in solution)
- D. But-1-ene and but-2-ene differ in position of double bond $\rightarrow$ IV. Position isomers
### Step 1: Final Conclusion
Matching respective pairs correctly yields option (2): A-III, B-I, C-II, D-IV.
### Pattern Recognition
Sees: Match list of isomerism pairs.
Trap: Mixing up position and chain isomers for alkenes.
### Chapter Mix
Class 11 Chemistry: Organic Chemistry - Some Basic Principles and Techniques
Q62 (2026)
The correct order of the rate of the reaction for the following reaction with respect to nucleophiles is:
$$\text{CH}_3\text{Br} + \text{Nu}^{\ominus} \longrightarrow \text{CH}_3\text{Nu} + \text{Br}^{\ominus}$$
(1) $\text{PhO}^- > ^-\text{OH} > \text{CH}_3\text{COO}^- > \text{ClO}_4^-$
(2) $\text{ClO}_4^- > \text{CH}_3\text{COO}^- > ^-\text{OH} > \text{PhO}^-$
(3) $\text{CH}_3\text{COO}^- > \text{PhO}^- > ^-\text{OH} > \text{ClO}_4^-$
(4) $^-\text{OH} > \text{PhO}^- > \text{CH}_3\text{COO}^- > \text{ClO}_4^-$
- $(1) \ \text{PhO}^- > ^-\text{OH} > \text{CH}_3\text{COO}^- > \text{ClO}_4^-$
- $(2) \ \text{ClO}_4^- > \text{CH}_3\text{COO}^- > ^-\text{OH} > \text{PhO}^-$
- $(3) \text{CH}_3\text{COO}^- > \text{PhO}^- > ^-\text{OH} > \text{ClO}_4^-$
- $(4) \ ^-\text{OH} > \text{PhO}^- > \text{CH}_3\text{COO}^- > \text{ClO}_4^-$
### Core Logic
Nucleophilicity generally parallels basicity among related species (when comparing oxygen-centered nucleophiles in similar environments). Stability order of corresponding conjugate acids/anions is reverse of nucleophilicity or basicity strength.
Basicity/Nucleophilicity order: $^-\text{OH} > \text{PhO}^- > \text{CH}_3\text{COO}^- > \text{ClO}_4^-$.
### Step 1: Final Conclusion
Thus, option (4) represents the correct nucleophilicity order.
### Pattern Recognition
Sees: Nucleophilic substitution rate and nucleophilicity order.
Trap: Confusing leaving group ability with nucleophile strength.
### Chapter Mix
Class 11 Chemistry: Organic Chemistry - Some Basic Principles and Techniques
Q68 (2026)
Given below are two statements:
Statement I: Compound (X), shown below, dissolves in $\text{NaHCO}_3$ solution and has two chiral carbon atoms.
{{IMG1}}
Statement II: Compound (Y), shown below, has two carbons with $sp^3$ hybridization, one carbon with $sp^2$ and one carbon with $sp$ hybridization.
{{IMG2}}
In the light of the above statements, choose the correct answer from the options given below:
- $(1) \text{ Statement I is true but Statement II is false}$
- $(2) \text{ Statement I is false but Statement II is true}$
- $(3) \text{ Both Statement I and Statement II are true}$
- $(4) \text{ Both Statement I and Statement II are false}$
### Core Logic
- Statement I: Compound X contains a carboxylic acid group (which dissolves in $\text{NaHCO}_3$) and possesses two chiral centers. Thus Statement I is true.
- Statement II: Compound Y has specific carbon hybridization states matching $sp^3$, $sp^2$, and $sp$ carbons. Thus Statement II is true.
### Step 1: Final Conclusion
Both Statement I and Statement II are true, matching option (3).
### Pattern Recognition
Sees: identification of chiral centers and carbon hybridization in organic molecules.
Trap: Overlooking carboxylic acid solubility requirements in $\text{NaHCO}_3$.
### Chapter Mix
Class 11 Chemistry: Organic Chemistry - Some Basic Principles and Techniques
