Engineering Chemistry MCQ (Carbanions)

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Engineering Chemistry MCQ (Carbanions)

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1. Select the correct statement from the following option.
a) Carbanion is the intermediate compound
b) In carbanion, central carbon atom carries negative charge
c) It possess an unshared pair of electron
d) All of the mentioned
Answer: d
Explanation: Carbanion is the intermediate compound in which central carbon atom
carries a negative charge and it possess the unshared pair of electron. It is an anion
in which carbon has an unshared pair of electrons and bears a negative charge
usually with three substituents for a total of eight valence electrons.

2. The hybridisation of carbanion is ____________
a) Sp
b) Sp2
c) Sp3
d) Sp3d
Answer: c
Explanation: The hybridisation of carbanion is sp3 . A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons.

3. The formal charge at the carbanion is ___________
a) +1
b) -1
c) 0
d) +2
Answer: b
Explanation: The formal charge at the carbanion is -1. A carbanion is an anion in
which carbon has an unshared pair of electrons and bears a negative charge usually
with three substituents for a total of eight valence electrons.

4. The geometry of carbanion is ___________
a) Pyramidal
b) Linear
c) Tetrahedral
d) Trigonal planar
Answer: a
Explanation: The geometry of carbanion is pyramidal. A carbanion is an anion in
which carbon has an unshared pair of electrons and bears a negative charge usually
with three substituents for a total of eight valence electrons.

5. The structure of carbanion is pyramidal but it undergoes rapid inversion similar to those of amines.
a) True
b) False
Answer: a
Explanation: The structure of carbanion is pyramidal but it undergoes rapid
inversion similar to those of amines. The carbanion exists in a trigonal pyramidal
geometry. Formally, a carbanion is the conjugate base of a carbon acid.

6. Negative charge of carbanion can be dispersed by ___________
a) (+I) effect and resonance
b) (-I) effect and resonance
c) Hyperconjugation
d) (+M) effect and resonance
Answer: b
Explanation: Negative charge of carbanion can be dispersed by (+I) effect and
resonance. A carbanion is a nucleophile. The stability and reactivity of a carbanion is determined by several factors.

7. Which of the following carbanion is least stable?
a) 10
b) 20
c) 30
d) CH3
Answer: c
Explanation: 30 carbanion is the least stable carbanion. The same factors that
determine the stability of the carbanion also determine the order in pKa in carbon acids.

8. Which of the following carbanion is most stable?
a) 10
b) 20
c) 30
d) CH3
Answer: d
Explanation: CH3 carbanion is the most stable carbanion. The same factors that
determine the stability of the carbanion also determine the order in pKa in carbon acids.

9. On increasing the number of alkyl groups, the stability of carbanions ___________
a) Increases
b) Decreases
c) Remains same
d) None of the mentioned
Answer: b
Explanation: On increasing the number of alkyl groups, the stability of carbanions decreases. The alkyl groups have (-I) effect.

10. Due to (+I) effect, the methyl groups are electron accepting in nature.
a) True
b) False
Answer: b
Explanation: Due to (+I) effect, the methyl groups are electron releasing in nature.
The same factors that determine the stability of the carbanion also determine the
order in pKa in carbon acids.