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CHXII10:HALOALKANES AND HALOARENES

322826 Assertion :
4-Nitrochlorobenzene undergoes nucleophilie substitution readily more than chlorobenzene.
Reason :
Chlorobenzene undergoes nucleophilic substitution by elimination-addition mechanism while 4-nitrochlorobenzene undergoes nucleophilic substitution by addition-elimination mechanism.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Assertion is incorrect but Reason is correct.

Explanation:

Compared to chlorobenzene, the intermediate carbanion formed from 4-nitrochlorobenzene experiences stabilization due to the -R effect of the ${NO}_{2}$ group. Given reason is correct, but not the correct explanation for given assertion. So option (2) is correct.

CHXII10:HALOALKANES AND HALOARENES

322827 Order of reactivity towards nucleophilic substitution reaction of the compounds
supporting img

1 I >II > III > IV

2 II

>

I

>

III

>

IV

3 IV

>

III

>

II

>

I

4 III > IV > II > I

CHXII10:HALOALKANES AND HALOARENES

322828 Assertion :
Presence of nitro group facilitates nucleophilic substitution reactions in aryl halides.
Reason :
The intermediate carbanion is stable due to the presence of nitro group.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Both Assertion and Reason are incorrect.

Explanation:

Nitro group is an electron withdrawing (-I) group, it stabilises the carbanion because it disperses the negative charge on the carbon by attracting electrons.
Hence, both (A) and (R) are correct and (R) is the correct explanation of $(A)$ .

AIIMS - 2017

CHXII10:HALOALKANES AND HALOARENES

322829 Aryl halides are extremely less reactive towards nucleophilic substitution than alkyl halides.
Which of the following accounts for this?
(I) Due to resonance in aryl halides.
(II) In alkyl halides, carbon atom in $C - X$ bond is ${sp}^{2}$ hybridized whereas in aryl halides carbon atom in $C - X$ bond is ${sp}^{3}$ hybridized.
(III) Due to stability of phenyl cation.
(IV)Due to possible repulsion there are less chances of nucleophile to approach electron rich arenes.

1 (I), (II) and (IV)

2 (I), (II) and (III)

3 (I) and (IV)

4 (II), (III) and (IV)

Explanation:

(ii) and (iii) are incorrect as carbon of alkyl halide and aryl halide is ${sp}^{3}$ and ${sp}^{2}$ hybridized, respectively. Also phenyl cation is highly unstable. Aryl halides are less reactive towards SN reactions due to resonance and possible repulsion there are less chances of nucleophile to approach $e^{-}$ rich arenes.

CHXII10:HALOALKANES AND HALOARENES

322826 Assertion :
4-Nitrochlorobenzene undergoes nucleophilie substitution readily more than chlorobenzene.
Reason :
Chlorobenzene undergoes nucleophilic substitution by elimination-addition mechanism while 4-nitrochlorobenzene undergoes nucleophilic substitution by addition-elimination mechanism.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Assertion is incorrect but Reason is correct.

Explanation:

Compared to chlorobenzene, the intermediate carbanion formed from 4-nitrochlorobenzene experiences stabilization due to the -R effect of the ${NO}_{2}$ group. Given reason is correct, but not the correct explanation for given assertion. So option (2) is correct.

CHXII10:HALOALKANES AND HALOARENES

322827 Order of reactivity towards nucleophilic substitution reaction of the compounds
supporting img

1 I >II > III > IV

2 II

>

I

>

III

>

IV

3 IV

>

III

>

II

>

I

4 III > IV > II > I

CHXII10:HALOALKANES AND HALOARENES

322828 Assertion :
Presence of nitro group facilitates nucleophilic substitution reactions in aryl halides.
Reason :
The intermediate carbanion is stable due to the presence of nitro group.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Both Assertion and Reason are incorrect.

Explanation:

Nitro group is an electron withdrawing (-I) group, it stabilises the carbanion because it disperses the negative charge on the carbon by attracting electrons.
Hence, both (A) and (R) are correct and (R) is the correct explanation of $(A)$ .

AIIMS - 2017

CHXII10:HALOALKANES AND HALOARENES

322829 Aryl halides are extremely less reactive towards nucleophilic substitution than alkyl halides.
Which of the following accounts for this?
(I) Due to resonance in aryl halides.
(II) In alkyl halides, carbon atom in $C - X$ bond is ${sp}^{2}$ hybridized whereas in aryl halides carbon atom in $C - X$ bond is ${sp}^{3}$ hybridized.
(III) Due to stability of phenyl cation.
(IV)Due to possible repulsion there are less chances of nucleophile to approach electron rich arenes.

1 (I), (II) and (IV)

2 (I), (II) and (III)

3 (I) and (IV)

4 (II), (III) and (IV)

Explanation:

(ii) and (iii) are incorrect as carbon of alkyl halide and aryl halide is ${sp}^{3}$ and ${sp}^{2}$ hybridized, respectively. Also phenyl cation is highly unstable. Aryl halides are less reactive towards SN reactions due to resonance and possible repulsion there are less chances of nucleophile to approach $e^{-}$ rich arenes.

CHXII10:HALOALKANES AND HALOARENES

322826 Assertion :
4-Nitrochlorobenzene undergoes nucleophilie substitution readily more than chlorobenzene.
Reason :
Chlorobenzene undergoes nucleophilic substitution by elimination-addition mechanism while 4-nitrochlorobenzene undergoes nucleophilic substitution by addition-elimination mechanism.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Assertion is incorrect but Reason is correct.

Explanation:

Compared to chlorobenzene, the intermediate carbanion formed from 4-nitrochlorobenzene experiences stabilization due to the -R effect of the ${NO}_{2}$ group. Given reason is correct, but not the correct explanation for given assertion. So option (2) is correct.

CHXII10:HALOALKANES AND HALOARENES

322827 Order of reactivity towards nucleophilic substitution reaction of the compounds
supporting img

1 I >II > III > IV

2 II

>

I

>

III

>

IV

3 IV

>

III

>

II

>

I

4 III > IV > II > I

CHXII10:HALOALKANES AND HALOARENES

322828 Assertion :
Presence of nitro group facilitates nucleophilic substitution reactions in aryl halides.
Reason :
The intermediate carbanion is stable due to the presence of nitro group.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Both Assertion and Reason are incorrect.

Explanation:

Nitro group is an electron withdrawing (-I) group, it stabilises the carbanion because it disperses the negative charge on the carbon by attracting electrons.
Hence, both (A) and (R) are correct and (R) is the correct explanation of $(A)$ .

AIIMS - 2017

CHXII10:HALOALKANES AND HALOARENES

322829 Aryl halides are extremely less reactive towards nucleophilic substitution than alkyl halides.
Which of the following accounts for this?
(I) Due to resonance in aryl halides.
(II) In alkyl halides, carbon atom in $C - X$ bond is ${sp}^{2}$ hybridized whereas in aryl halides carbon atom in $C - X$ bond is ${sp}^{3}$ hybridized.
(III) Due to stability of phenyl cation.
(IV)Due to possible repulsion there are less chances of nucleophile to approach electron rich arenes.

1 (I), (II) and (IV)

2 (I), (II) and (III)

3 (I) and (IV)

4 (II), (III) and (IV)

Explanation:

(ii) and (iii) are incorrect as carbon of alkyl halide and aryl halide is ${sp}^{3}$ and ${sp}^{2}$ hybridized, respectively. Also phenyl cation is highly unstable. Aryl halides are less reactive towards SN reactions due to resonance and possible repulsion there are less chances of nucleophile to approach $e^{-}$ rich arenes.

CHXII10:HALOALKANES AND HALOARENES

322826 Assertion :
4-Nitrochlorobenzene undergoes nucleophilie substitution readily more than chlorobenzene.
Reason :
Chlorobenzene undergoes nucleophilic substitution by elimination-addition mechanism while 4-nitrochlorobenzene undergoes nucleophilic substitution by addition-elimination mechanism.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Assertion is incorrect but Reason is correct.

Explanation:

Compared to chlorobenzene, the intermediate carbanion formed from 4-nitrochlorobenzene experiences stabilization due to the -R effect of the ${NO}_{2}$ group. Given reason is correct, but not the correct explanation for given assertion. So option (2) is correct.

CHXII10:HALOALKANES AND HALOARENES

322827 Order of reactivity towards nucleophilic substitution reaction of the compounds
supporting img

1 I >II > III > IV

2 II

>

I

>

III

>

IV

3 IV

>

III

>

II

>

I

4 III > IV > II > I

CHXII10:HALOALKANES AND HALOARENES

322828 Assertion :
Presence of nitro group facilitates nucleophilic substitution reactions in aryl halides.
Reason :
The intermediate carbanion is stable due to the presence of nitro group.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Both Assertion and Reason are incorrect.

Explanation:

Nitro group is an electron withdrawing (-I) group, it stabilises the carbanion because it disperses the negative charge on the carbon by attracting electrons.
Hence, both (A) and (R) are correct and (R) is the correct explanation of $(A)$ .

AIIMS - 2017

CHXII10:HALOALKANES AND HALOARENES

322829 Aryl halides are extremely less reactive towards nucleophilic substitution than alkyl halides.
Which of the following accounts for this?
(I) Due to resonance in aryl halides.
(II) In alkyl halides, carbon atom in $C - X$ bond is ${sp}^{2}$ hybridized whereas in aryl halides carbon atom in $C - X$ bond is ${sp}^{3}$ hybridized.
(III) Due to stability of phenyl cation.
(IV)Due to possible repulsion there are less chances of nucleophile to approach electron rich arenes.

1 (I), (II) and (IV)

2 (I), (II) and (III)

3 (I) and (IV)

4 (II), (III) and (IV)

Explanation:

(ii) and (iii) are incorrect as carbon of alkyl halide and aryl halide is ${sp}^{3}$ and ${sp}^{2}$ hybridized, respectively. Also phenyl cation is highly unstable. Aryl halides are less reactive towards SN reactions due to resonance and possible repulsion there are less chances of nucleophile to approach $e^{-}$ rich arenes.

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