Carbocation Stability Questions and Answers

Content Writer-SME

Carbocation stability is one of the important parameters in chemistry that gives the information about the strength and potential of carbon compounds to remain unchanged under unfavorable conditions.

Here we have mentioned some important questions related to carbon stability which are frequently asked in boards and competitive exams such as NEET and JEE.

Carbocation Stability Questions

Ques. Which is the most stable form of carbon found in nature?

Ans. The thermodynamically stable structure is graphite while diamond is considered to be the kinetically stable structure of carbon. The presence of one delocalized electron per carbon in graphite contributes to a more stable structure because of the strong attraction of carbon atoms.

Ques. What are the factors that influence the carbon stability in compounds?

Ans. The potential of carbon to resist various chemical reactions such as oxidation, reduction, and decomposition. Here are some important factors that influence the stability of carbon are as follows:

Bond Strength: There is a direct relationship between the bond strength and carbon stability. This implies that the stronger bond between carbon-carbon, carbon-hydrogen, and carbon-oxygen contributes to the higher carbon stability.

Structure: The overall stability of carbon is enhanced by the presence of stable functional groups such amide, aromatic rings, etc.

Environmental Conditions: The stability of carbon is also disturbed by unfavorable change in temperature and pressure. Moreover, addition of catalysts or any reactive agent can also affect the carbon stability.

Ques. How stable carbon compounds help in mitigating climate change?

Ans. Stable carbon compounds in soil and oceans play an important role in maintaining carbon balance in the environment by acting as long-term carbon sinks. These carbon sinks help remove greenhouse gas emissions from the environment. Thus, stable carbon compounds help mitigate climate change.

Ques. How does carbon stability play a role in improving agricultural productivity?

Ans. The organic carbon products of the soil are considered as stable carbon. With increase in carbon content in soil, the carbon dioxide present in the atmosphere gradually decreases.

This provides a favorable environment and conditions for the growth and development of plants.
Moreover, the biological phenomena of carbon cycle is also stabilized by the presence of organic carbon in soil which further enhances agricultural productivity.

Ques. How does the hybridization of vinylic carbocation differ from phenyl carbocation?

Ans. The vinylic carbocation and phenyl carbocation differ from each other in terms of hybridisation and stability. The vinylic carbocation possess sp hybridization whereas phenyl carbocation have sp3 hybridized structure.

Ques. What is the relationship between electronegativity and stability of carbocations?

Ans. The physical property that describes the potential of a carbon atom to attract electrons towards itself is called electronegativity. There is the direct relationship between electronegativity and force of attraction between atoms and electrons.

However, there is an inverse relationship between carbocation stability and electronegativity.
This implies that, with increase in the electronegativity of carbocation, the stability decreases.
Therefore, the order of carbocation stability is given as:

Sp_c > Sp²_c > Sp³_c

Carbocation Stability MCQs

In this section, we have mentioned Carbon Stability MCQs with answers that are frequently asked in competitive exams such as NEET, JEE Main, JEE Advanced, IIT JAM, and other entrance exams:

Ques. The order of carbocation stability is given as:

Spc > Sp²c > Sp³c

Sp²c > Sp³c > Spc

Sp³c > Sp²c > Spc

None of the above

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Ans. a. Spc > Sp²c > Sp³c

Explanation: The presence of s character in sp hybridization is 50% which makes the structure most stable. In sp3 hybridized structure, the s character is present 33.33% which makes it a less stable structure.

Ques. What is the order of carbocation stability?

1^o carbocation >2^o carbocation >3^o carbocation> Methyl carbocation
2^o carbocation > 3^o carbocation > 1^ocarbocation > Methyl carbocation
3^o carbocation > 2^o carbocation > 1^o carbocation > Methyl carbocation
None of these

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Ans. c. 3^o carbocation > 2^o carbocation > 1^o carbocation > Methyl carbocation

Explanation: 3^o carbocation, also called tertiary carbocation is considered the most stable carbocation. Moreover, the order of stability of carbocation is given as:

Tertiary carbocation> Secondary carbocation> Primary carbocation> Methyl carbocation

Ques. Which of the following factors influence the stability of carbocation?

+M Effect
Resonance, and Hyperconjugation,
Inductive Effect
All of the above

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Ans. d. All of the above.

Explanation: The four important factors that influence carbocation stability are as follows:

+M Effect
Resonance
Hyperconjugation, and
Inductive Effect

Ques. Which of the following is the most stable carbocation? (NEET 2024)

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Ans. d.

Explanation: Option d is the structure of p-methyl benzene which is a most stable carbocation structure among all. In this, carbon stability is enhanced by the presence of a methyl group that takes part in hyperconjugation.

Ques. Which of the following is considered as the most stable carbocation aromatic structure? (NEET 2024)

’

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Ans. c.

Explanation: NO2 is considered as an electron-withdrawing group which implies that the presence of NO2 at ortho and para position of an aromatic ring structure increases the electron density.

The other factor that affects the carbocation stability is –I effect (inductive effect).
With increase in –I effect, the stability of carbocation decreases.
In option (c), the distance between positive charge and –N is maximum, thus the –I effect decreases which in turn increases the carbocation stability.