The most suitable reagent for the conversion of is
1
2
3
4
(pyridine chloro chromate)
Official Solution
Correct Option: (4)
Pyridinium chlorochromate (PCC) is a very good oxidising agent for converting alcohol to aldehydes and alcohols to ketone. It prevents further oxidation of aldehydes to carboxylic acid.
[PCC is prepared by mixing pyridine and . Carboxylic acid aldehyde
02
PYQ 2019
medium
chemistryID: jee-main
The product formed in the reaction of cumene with followed by treatment with dil. are :
1
2
3
4
Official Solution
Correct Option: (3)
The correct answer is C:Cummene hydroperoxide reaction
03
PYQ 2021
medium
chemistryID: jee-main
Reaction of Grignard reagent, C₂H₅MgBr with C₈H₈O followed by hydrolysis gives compound "A" which reacts instantly with Lucas reagent to give compound B, C₁₀H₁₃Cl. The Compound B is :
1
A
2
B
3
C
4
D
Official Solution
Correct Option: (4)
Step 1: is Acetophenone ( ).
Step 2: Reaction with : The ethyl group attacks the carbonyl carbon to form a tertiary alcohol, 2-phenylbutan-2-ol ( ).
Step 3: **Lucas reagent** ( ) reacts **instantly** only with tertiary alcohols.
Step 4: Replacement of with gives . (Note: formula matches).
04
PYQ 2021
medium
chemistryID: jee-main
Identify products A and B.
1
A
2
B
3
C
4
D
Official Solution
Correct Option: (1)
Step 1: Alkanes with a tertiary H-atom are oxidized to tertiary alcohols by . Thus, isobutane tert-butanol (A).
Step 2: is an oxidizing agent. However, tertiary alcohols are generally resistant to oxidation under these conditions.
*Note: In many exam variants, if the starting material is an alkene, A would be a diol and B a ketone. For isobutane, A is tert-butanol.*
05
PYQ 2022
medium
chemistryID: jee-main
A sample of 4.5 mg of an unknown monohydric alcohol, R–OH was added to methylmagnesium iodide. A gas is evolved and is collected and its volume measured to be 3.1 mL. The molecular weight of the unknown alcohol is___ g/mol. [Nearest integer]
Official Solution
Correct Option: (1)
The reaction between a monohydric alcohol (R–OH) and methylmagnesium iodide (an organometallic compound) can be represented as follows:
This reaction liberates methane (CH4) gas as 3.1 mL. We need to find the molecular weight of the unknown alcohol.
To find the amount (in moles) of CH4 gas evolved, use the Ideal Gas Law at standard temperature and pressure (STP):
1 mole of gas at STP occupies 22.4 L or 22400 mL.
Moles of CH4 =
Moles of CH4 =
The moles of R–OH are equivalent to the moles of CH4 since 1 mole of R–OH generates 1 mole of CH4 gas.
Given mass of R–OH = 4.5 mg = 0.0045 g
Molecular weight of R–OH =
Molecular weight =
Rounding to the nearest integer, the molecular weight of the unknown alcohol is 32 g/mol.
This calculated value of 32 g/mol does not fall within the 33-33 range, indicating potential non-STP conditions or additional factors not explicitly stated in the problem may affect this result. Verification of experimental conditions is advised.
06
PYQ 2022
medium
chemistryID: jee-main
Which one of the following reactions does not represent correct combination of substrateand product under the given conditions?
1
2
3
4
Official Solution
Correct Option: (4)
Na2Cr2O7, H2SO4/H2O is the strongest oxidising agent and it will oxidise 1° alcohol into acids.
So, the correct option is (D).
07
PYQ 2022
medium
chemistryID: jee-main
Which of the following reagents/reactions will convert ‘A’ to ‘B’?
1
PCC oxidation
2
Ozonolysis
3
, / followed by PCC oxidation
4
HBr, hydrolysis followed by oxidation by .
Official Solution
Correct Option: (3)
The first step involves addition of to alkene according to anti-markownikoff’s rule while the second step involves oxidation of 1° alcohol to aldehyde.
So, the correct option is (C):, /followed by PCC oxidation.
08
PYQ 2022
easy
chemistryID: jee-main
In the given reaction
Fig.
the number of sp2 hybridised carbon(s) in compound ‘X’ is _____.
Official Solution
Correct Option: (1)
The correct answer is 8
Fig.
Note that phenyl ring has sp2 carbons as well.
09
PYQ 2023
hard
chemistryID: jee-main
Choose the correct colour of the product for the following reaction
1
Blue
2
White
3
Red
4
Yellow
Official Solution
Correct Option: (3)
This is an example of a diazo coupling reaction, where a diazonium salt reacts with 1-naphthylamine to form an azo dye. The product is red in colour due to the extensive conjugation in the azo compound.
10
PYQ 2024
hard
chemistryID: jee-main
Which of the following compounds has the highest boiling point?
1
Butanol
2
Diethylether
3
Butane
4
Butanol
Official Solution
Correct Option: (1)
The correct option is (A):Butanol
11
PYQ 2026
medium
chemistryID: jee-main
3,3-Dimethyl-2-butanol cannot be prepared by: (A) Reaction of the given aldehyde with MeMgBr followed by H3O+
(B) Acid-catalysed hydration of the given alkene
(C) Ozonolysis followed by reduction using NaBH4/MeOH
(D) Reduction using LiAlH4/H3O+
(E) Acid-catalysed hydration of the given alkyne using Hg2+/H+
Choose the correct answer from the options given below:
1
B, C and E only
2
B and C only
3
B and E only
4
B only
Official Solution
Correct Option: (3)
The target compound is 3,3-dimethyl-2-butanol, which is a secondary alcohol.
Step 1: Analyze option (A). Reaction of an aldehyde with followed by acidic workup gives a secondary alcohol. The given aldehyde structure leads to the formation of 3,3-dimethyl-2-butanol. Hence, option (A) can prepare the given alcohol.
Step 2: Analyze option (B). Acid-catalysed hydration of the given alkene proceeds via a carbocation intermediate. Due to rearrangement (hydride or alkyl shift), the product formed is not 3,3-dimethyl-2-butanol. Hence, option (B) cannot prepare the given alcohol.
Step 3: Analyze option (C). Ozonolysis followed by reductive workup cleaves the double bond to give carbonyl compounds, which on reduction yield alcohols. However, the given alkene skeleton does not regenerate the required carbon framework of 3,3-dimethyl-2-butanol. Hence, option (C) cannot prepare the given alcohol.
Step 4: Analyze option (D). Reduction of the given ketone using followed by acidic workup gives the corresponding secondary alcohol. Thus, option (D) can prepare 3,3-dimethyl-2-butanol.
Step 5: Analyze option (E). Acid-catalysed hydration of terminal alkynes using gives ketones (via enol–keto tautomerism), not alcohols. Hence, option (E) cannot prepare the given alcohol.
Step 6: Final conclusion. The methods which cannot prepare 3,3-dimethyl-2-butanol are B and E.
