This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Resonance and Aromaticity”.
1. Resonance forms are in equilibrium with each other. State true or false
Explanation: Resonance forms are hybrid in nature and hence it is not correct to say that they are in equilibrium with each other.
2. Identify the false statement regarding resonance
a) As the number of charges increases, the resonance forms gets more significant
b) Zero charge of resonance is the most significant one
c) Atoms with full octet resonance form are more stable when compared with the one with unfilled octet
d) Resonance is unstable in case of unfilled octet of nitrogen atom
Explanation: Greater the number of charges, less stable and less significant gets the resonance form.
3. Identify the correct sequence according to electronegativity
a) F> NH2> CH3>OH`
b) NH2`> F`>CH3`> OH`
c) NH2`>OH`> CH3`>F`
d) F`> OH`>NH2`>CH3`
Explanation: In the sequence ” F`> OH`> NH2`> CH3`”, F’ is the most stable one and CH3′ is the least stable one, as the stability of the anions increases on moving towards the right of the periodic table.
4. Identify the correct sequence with respect to Inductive effects
a) CF3`> CH2F`> CHF2`> CF3`
b) CF3`> CHF2`> CH2F`> CH3`
c) CH3`> CH2F`> CHF2`> CF3`
d) CH3`> CHF2`> CH2F`v CF3`
Explanation: As electron withdrawing substituent is greater in CF3, it is more stable and CH3 is the least stable one and hence the sequence.
5. Stability sequence: primary carbocation> secondary carbocation > tertiary carbocation.
Is this sequence correct?
Explanation: The tertiary carbocation has the highest stability and the primary carbocation has the least stability, as it lies close to electron withdrawing group and hence the sequence is not correct.
6. Identify the incorrect statement regarding aromaticity
a) It is the extra stability possessed by a molecule
b) p-orbitals must be planar and overlap
c) Cyclic delocalization takes place
d) It does not follow Huckel’s rule
Explanation: It follows Huckel’s rule, according to which a molecule must possess specific number of pi electrons within a closed ring of p-orbitals.
7. Aromatic rings do not have resonance structures. State true or false
Explanation: Aromatic rings have resonance structure due to cycling double bonds and all aromatic rings must have resonance but the converse need not be satisfied.
8. Select the correct statement regarding the aromatic nitrogen molecule
a) It is not hybridized
b) It is sp hybridized
c) It is sp2 hybridized
d) It is sp3 hybridized
Explanation: As a result of its overall structure and electron delocalization, it becomes a sp2 hybridized, aromatic molecule.
9. Can a linear molecule have aromaticity?
Explanation: A molecule can have aromaticity if it is closed loop or ring-shaped or has p-orbitals and hence linear molecule cannot have aromaticity.
10. Select the incorrect statement:
a) A resonance may sometimes cause sp3 atoms to become sp2 hybridized
b) Delocalizing one lone pair causes aromaticity
c) One lone pair will be counted as two pi electrons according to Huckel’s equation
d) Two sigma bonds make up a double bond
Explanation: A double bond is one which has a sigma bond and a pi bond. Each pi bond has two pi electrons.
Sanfoundry Global Education & Learning Series – Organic Chemistry.
To practice all areas of Organic Chemistry, here is complete set of 1000+ Multiple Choice Questions and Answers.