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Organic Reactions

Description: GATE CHEMISTRY, LIFE SCIENCE, ENGINEERING
Number of Questions: 15
Created by:
Tags: GATE Aromatic Electrophilic Substitution Addition Reactions Elementary Treatment of SN1, SN2, E1 and E2 Reactions Acids and Bases
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Which of the following statements is/are true? A. Benzene reacts with isobutyl chloride in presence of anhydrous AlCl3 to give isobutyl benzene. B. Bayer’s reagent can be used to distinguish cyclopropane from propene. C. Ethyne and its derivatives give white precipitate with ammoniacal silver nitrate solution.

  1. Only A

  2. Only B

  3. Only C

  4. Both A and B

  5. Both B and C

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Correct Option: B
Explanation:

This option is correct, because propene decolourises Bayer’s reagent but cyclopropane being saturated does not.

Assertion: Reaction of 1, 3-dibromopropane with zinc produces cyclopropane. Reason: The reaction of alkyl halides with zinc dust is called Frankland reaction.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

This option is correct, because the two carbon atoms carrying the Br-atoms in 1, 3-dibrobopropane are close, and hence undergo intermolecular cyclisation to give cyclopropane.

Assertion: Fredel-Crafts reaction of benzene with n-propyl chloride gives isopropylbenzene. Reason: Benzene undergoes electrophilic substitution readily.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

This option is correct because the initially formed n-propyl cation first undergoes rearrangement by 1, 2-hydride shift to more stable isopropyl cation, which then attacks the benzene ring to form isopropylbenzene.

Assertion: Benzene reacts with Cl2 in presence of light to form BHC. Reason: BHC is also called gammexane or 666.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

This option is correct because in presence of light, free radical addition of Cl2 occurs to the three double bonds giving BHC.

Assertion: Addition of HI to vinyl chloride produces 1-chloro-1-iodoethene. Reason: HI adds to vinyl chloride against Markownikov’s rule.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: C
Explanation:

This option is correct, because HI adds to vinyl chloride according to Markownikov’s rules.

Assertion: Propene is more reactive than ethene towards electrophilic addition reactions. Reason: Hyperconjugation effect of the CH3 group increases the electron density in the double bond.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: A
Explanation:

Propene is more reactive than ethene towards electrophilic addition reactions because of hyperconjugation effect of the CH3 group increases the electron density in the double bond. Thus, this option is correct.

Assertion: Addition of Br2 to maleic acid gives (+) and (-) forms of the product. Reason: Addition of Br2 to maleic acid follows trans-addition.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: A
Explanation:

This option is correct because both assertion and reason are true and reason, 'addition of Br2 to maleic acid follows trans-addition' is the correct explanation of assertion.

Assertion: Both cyclopropane and propene give addition reactions readily. Reason: Cyclopropane and propene are isomers of each other.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

This option is correct because propene being unsaturated undergoes addition reactions. In contrast, cyclopropane being strained readily undergoes ring cleavage to yield addition products.

Assertion: Propene reacts with perbenzoic acid to produce 1, 2-epoxypropane. Reason: In this reaction, propene acts as a nucleophile.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: A
Explanation:

This option is correct, because propene acts as a nucleophile and reacts with perbenzoic acid to produce 1, 2-epoxypropane.

Assertion: 2, 3-Dimethylbut-2-ene is more stable than but-2-ene. Reason: Twelve hyperconjugation structures can be written for 2, 3-Dimethylbut-2-ene while but-2-ene has only six.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: A
Explanation:

This option is correct, because 2, 3-dimethylbut-2-ene has twelve hyperconjugation structures and but-2-ene has only six, due to this 2, 3-dimethylbut-2-ene is more stable than but-2-ene.

Assertion: Acetylene reacts with sodamide to evolve H2 gas. Reason: Acetylene is a weaker acid than ammonia.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: E
Explanation:

This option is correct because acetylene reacts with sodamide to evolve NH3, i.e. HC≡CH + NaNH2 → HC≡CNa + NH3 and it is a stronger acid than ammonia.

Assertion: Acidity of the C-H bond decreases in the order; HC≡CH > H2C=CH2 > H3C−CH3. Reason: Acidity of the C-H bond increases as the electronegativity of the carbon to which it is attached increases.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: A
Explanation:

This option is correct because the acidity of the C-H bond increases as the electronegativity of the carbon to which it is attached increases.

Assertion: Addition of H2O to acetylene occurs in presence of dil. H2SO4 and HgSO4 to give acetaldehyde. Reason: It is an example of electrophilic addition reaction.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

This option is correct, because Hg+2 ion being an electrophile first complexes with the π-electrons of the triple bond and then nucleophile attack of H2O occurs.

Assertion: But-1-yne reacts with Tollen’s reagent to give white precipitate of silver but-1-ynide, but but-2-yne does not react. Reason: But-1-yne has acidic hydrogen but but-2-yne does not.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true but R is NOT the correct explanation of A.

  3. A is true but R is false.

  4. A is false but R is true.

  5. Both A and R are false.

Show answer
Correct Option: A
Explanation:

CH3−CH2−C=CH + [Ag(NH3)2]+OH- → CH3−CH2−C=C-Ag+ + 2NH3 + H2O But-1-yne reacts with Tollen’s reagent to give white precipitate of silver but-1-ynide because but-1-yne has acidic hydrogen, while but-2-yne does not react with Tollen’s reagent due to absence of acidic hydrogen. Thus, this option is correct.

Which of the following statements is/are false?

  1. Lindlar’s catalyst is palladium supported over calcium carbonate, but partially poisoned by addition of lead acetate.

  2. –COOCH3 is a meta-directing group while OCOCH3 is an ortho-, para- directing group.

  3. Both 1 and 2

  4. When acetylene reacts with methyl magnesium bromide, hydrogen is evolved.

  5. None of these

Show answer
Correct Option: D
Explanation:

This option is correct because when acetylene reacts with methyl magnesium bromide, CH4 is produced. HC≡CH + CH3MgBr → HC≡CMgBr + CH4

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