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Organic Chemistry: Structure and Electronic Effects

Advanced organic chemistry questions covering molecular orbital theory, aromaticity, hybridization, resonance, hyperconjugation, reactive intermediates, and chemical reaction mechanisms. Designed for GATE Chemistry, CSIR NET, and Life Sciences competitive exam preparation.

15 Questions Published
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Questions

Question 1 Multiple Choice (Single Answer)

Assertion: Six p-orbitals in benzene combine to form three bonding and three antibonding molecular orbitals.
Reason: Each bonding orbital contains a pair of electrons with opposite spins.

  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.
Question 2 Multiple Choice (Single Answer)

Assertion: The potential energy barrier for rotation about C=C bond in 2-butene is much higher than that in ethylene.
Reason: Hyperconjugation effect decreases the double bond character.

  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.
Question 3 Multiple Choice (Single Answer)

Assertion: [10]-Annulene is an aromatic because it contains Huckel number of π-electrons.
Reason: Steric interaction between internal hydrogen makes it non-planar.

  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.
Question 4 Multiple Choice (Single Answer)

Assertion: Azulene is a non-benzenoid compound.
Reason: It is planar, has a cyclic array of 10 π-electrons but does not contain benzene rings.

  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.
Question 5 Multiple Choice (Single Answer)

Assertion: The dipole moment of 1, 2-diphenylcyclopropenone is larger than that of benzophenone.
Reason: 1, 2-diphenylcyclopropenone is a cyclic compound while benzophenone is an open chain compound.

  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.
Question 6 Multiple Choice (Single Answer)

Assertion: Friedel-Crafts reaction between benzene and acetic anhydride in the presence of anhydrous AlCl3 yield.
Reason: Acetophenone formed poisons the catalyst preventing further 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.
Question 7 Multiple Choice (Single Answer)

Assertion: Cyclooctatetraene reacts with two equivalents of potassium to form a stable compound with formula 2K+ C8H82-.
Reason: Cyclooctatetraene is non-aromatic but 2K+ C8H82- is aromatic.

  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.
Question 8 Multiple Choice (Single Answer)

Assertion: A triplet carbene is more stable than a singlet carbene.
Reason: In triplet carbene, carbon atom is sp-hybridized while in singlet carbene it is sp2-hybridized.

  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.
Question 9 Multiple Choice (Single Answer)

Which of the following statements is/are correct?
A. Allene (CH2=C=CH2) is a planar molecule.
B. [14]-Annulene is aromatic while [10]-annulene is not aromatic.
C. The carbocation, F3C-C+ is less stable than the carbocation, F3C+.

  1. Only A
  2. Both A and B
  3. Both B and C
  4. A, B and C
  5. Both A and C
Question 10 Multiple Choice (Single Answer)

Carbon atoms of 1, 3-butadiene are numbered as shown below
CH2=CH−CH=CH2
Which of the following statements regarding the above compound is incorrect?
A. Carbon atoms 1 and 4 are sp2-hybridized.
B. The single bond between C2 and C3 is of the same length as the carbon-carbon bond length in ethane.
C. It is a conjugated diene.

  1. Only A
  2. Only B
  3. Only C
  4. Only B and C
  5. None of these
Question 11 Multiple Choice (Single Answer)

Which of the following statements is/are false?
A. The resonance energy of benzene is higher than its heat of hydrogenation.
B. The greater stability of trans-but-2-ene can be explained on the basis of hyperconjugation effect.
C. Dichlorocarbene (:CCl2) is a nucleophile.

  1. Only A
  2. Only B
  3. Only C
  4. Both A and C
  5. A, B and C
Question 12 Multiple Choice (Single Answer)

Which of the following statements is/are correct?

  1. Simple carbocations are isoelectronic and isostructural with ammonium.
  2. Resonance necessarily always imparts stability to a molecule.
  3. Both 1 and 2
  4. Electromeric is a temporary effect and takes place at the demand of the attacking reagents.
  5. None of these
Question 13 Multiple Choice (Single Answer)

Which of the following statements is/are incorrect?
A. Corey-House reaction can be used to prepare only alkenes with odd number of carbon atoms.
B. Reforming involves conversion of aliphatic into aromatic hydrocarbons.
C. The formation of alkenes by the action of zinc on alkyl halides is called Frankland reaction.

  1. Only A
  2. Only B
  3. Only C
  4. A and C
  5. A, B and C
Question 14 Multiple Choice (Single Answer)

Which of the following statements is/are incorrect?
A. In two step reaction, the rate determining step has the lowest energy of activation.
B. All the carbon atoms in bicyclobutane are sp3-hybridized.
C. Free radicals are produced by homolytic cleavage of covalent bonds.

  1. Only A
  2. Only B
  3. Only C
  4. A, B and C
  5. None of these
Question 15 Multiple Choice (Single Answer)

Assertion: N3- is weaker base than NH2-.
Reason: The lone pair of electron on N-atom in N3- is in a sp2-orbital while in NH2- it is in a sp3-orbital.

  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.
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