Electrophiles, nucleophiles and stability of intermediates — practice questions

Question 1 · difficulty L2 · understanding

Given below are two statements : Statement I : On the basis of inductive effect, the order of stability of alkyl carbanions is $\mathrm{CH}_3{ }^{-}>\mathrm{CH}_3-\mathrm{CH}_2{ }^{-}>\left(\mathrm{CH}_3\right)_2 \mathrm{CH}^{-}>\left(\mathrm{CH}_3\right)_3 \mathrm{C}^{-}$. Statement II : Allyl and benzyl carbanions are more stabilised by inductive effect and not by resonance effect. In the light of the above statements, choose the correct answer from the options given below :

• A. Both Statement I and Statement II are correct
• B. Both Statement I and Statement II are incorrect
• C. Statement I is correct but Statement II is incorrect
• D. Statement I is incorrect but Statement II is correct

Question 2 · difficulty L2 · understanding

Given below are two statements : Statement I : In , the carbocation is stabilised by +R effect of –OCH 3 group. Statement II : In , the carbanion is stabilised by –R effect of –NO 2 group. In the light of the above statements, choose the correct answer from the options given below :

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Question 3 · difficulty L2 · understanding

CORRECT order of stability for the following is $\mathrm{CH}_2=\mathrm{CH}^{-}, \mathrm{CH}_3-\mathrm{CH}_2^{-}, \mathrm{CH} \equiv \mathrm{C}^{-}$

• A. $\mathrm{CH} \equiv \mathrm{C}^{-}>\mathrm{CH}_3-\mathrm{CH}_2^{-}>\mathrm{CH}_2=\mathrm{CH}^{-}$
• B. $\mathrm{CH}_2=\mathrm{CH}^{-}>\mathrm{CH} \equiv \mathrm{C}^{-}>\mathrm{CH}_3-\mathrm{CH}_2^{-}$
• C. $\mathrm{CH} \equiv \mathrm{C}^{-}>\mathrm{CH}_2=\mathrm{CH}^{-}>\mathrm{CH}_3-\mathrm{CH}_2^{-}$
• D. $\mathrm{CH}_3-\mathrm{CH}_2^{-}>\mathrm{CH}_2=\mathrm{CH}^{-}>\mathrm{CH} \equiv \mathrm{C}^{-}$

Question 4 · difficulty L2 · understanding

Given below are two statements : Statement I : $\left(\mathrm{CH}_3\right)_3 \stackrel{\oplus}{\mathrm{C}}$ is more stable than $\stackrel{\oplus}{\mathrm{C}} \mathrm{H}_3$ as nine hyperconjugation interactions are possible in $\left(\mathrm{CH}_3\right)_3 \stackrel{\oplus}{\mathrm{C}}$. Statement II : $\stackrel{\oplus}{\mathrm{C}}\mathrm{H}_3$ is less stable than $\left(\mathrm{CH}_3\right)_3 \stackrel{\oplus}{\mathrm{C}}$ as only three hyperconjugation interactions are possible in $\stackrel{\oplus}{\mathrm{C}} \mathrm{H}_3$. In the light of the above statements, choose the correct answer from the options given below

• A. Statement I is false but Statement II is true
• B. Statement I is true but Statement II is false
• C. Both Statement I and Statement II are true
• D. Both Statement I and Statement II are false

Question 5 · difficulty L2 · understanding

Match the LIST-I with LIST-II LIST-I LIST-II A. Carbocation I. Species that can supply a pair of electrons. B. C-Free radical II. Species that can receive a pair of electrons. C. Nucleophile III. sp 2 hybridized carbon with empty p-orbital. D. Electrophile IV. sp 2 /sp 3 hybridized carbon with one unpaired electron. Choose the correct answer from the options given below:

• A. A-IV, B-II, C-III, D-I
• B. A-II, B-III, C-I, D-IV
• C. A-III, B-IV, C-I, D-II
• D. A-III, B-IV, C-II, D-I

Question 6 · difficulty L2 · understanding

Given below are two statements : Statement I : Hyperconjugation is not a permanent effect. Statement II : In general, greater the number of alkyl groups attached to a positively charged Cation, greater is the hyperconjugation interaction and stabilization of the cation. In the light of the above statements, choose the correct answer from the options given below

• A. Statement I is false but Statement II is true
• B. Statement I is true but Statement II is false
• C. Both Statement I and Statement II are false
• D. Both Statement I and Statement II are true

Question 7 · difficulty L2 · understanding

A species having carbon with sextet of electrons and can act as electrophile is called

• A. pentavalent carbon
• B. carbon free radical
• C. carbanion
• D. carbocation

Question 8 · difficulty L2 · understanding

The correct stability order of carbocations is

• A. $$\left(\mathrm{CH}_3\right)_3 \mathrm{C}^{+}>\mathrm{CH}_3-\stackrel{+}{\mathrm{C}} \mathrm{H}_2>\left(\mathrm{CH}_3\right)_2 \stackrel{+}{\mathrm{C}} \mathrm{H}>\stackrel{+}{\mathrm{C}} \mathrm{H}_3$$
• B. $$\left(\mathrm{CH}_3\right)_3 \stackrel{+}{\mathrm{C}}>\left(\mathrm{CH}_3\right)_2 \stackrel{+}{\mathrm{C}} \mathrm{H}>\mathrm{CH}_3-\stackrel{+}{\mathrm{C}} \mathrm{H}_2>\stackrel{+}{\mathrm{C}} \mathrm{H}_3$$
• D. $$\stackrel{+}{\mathrm{C}} \mathrm{H}_3>\left(\mathrm{CH}_3\right)_2 \stackrel{+}{\mathrm{C}} \mathrm{H}>\mathrm{CH}_3-\stackrel{+}{\mathrm{C}} \mathrm{H}_2>\left(\mathrm{CH}_3\right)_3 \stackrel{+}{\mathrm{C}}$$

Question 9 · difficulty L2 · understanding

In the following carbocation, H/CH$$_3$$ that is most likely to migrate to the positively charged carbon is :

• A. CH$$_3$$ at C-4
• B. H at C-4
• C. CH$$_3$$ at C-2
• D. H at C-2

Question 10 · difficulty L2 · understanding

The total number of contributing structure showing hyper-conjugation (involving C-H bonds) for the following carbocation is _________.