QBManager

GENERAL ORGANIC CHEMISTRY

231468 Arrange the following in decreasing order of acidic strength.
(i) Benzoic acid
(ii) 4-nitrobenzoic acid
(iii) 3, 4-dinitrobenzoic acid
(iv) 4-methoxy benzoic acid

1 III

>

II

>

I

>

IV

2 III

>

II

>

IV

>

I

3 II

>

III

>

IV

>

I

4 I

>

II

>

III

>

IV

Explanation:

Since, electron donating groups decrease the acid strength, therefore, 4-methoxy benzoic acid is a weaker acid than benzoic acid. Further, since electronwithdrawing groups increase the acid strength, therefore, both 4-nitrobenzoic acid and 3, 4dinitrobenzoic acid are stronger acid than benzoic acid. Further, due to presence of an additional ${NO}_{2}$ at $m$ position with respect to $COOH$ group, 3, 4dinitrobenzoic acid is a little stronger acid than 4- nitrobenzoic acid thus the overall acid strength increase in the order:
4-methoxy benzoic acid $<$ benzoic acid $<$ 4 - nitrobenzoic acid $< 3$ , 4-dinitrobenzoic acid.

JCECE - 2016

GENERAL ORGANIC CHEMISTRY

231470 Among the following which is least acidic?

1 Phenol

2 o-cresol

3 p-nitrophenol

4 p-chlorophenol

Explanation:

Nitro $(- {NO}_{2})$ and chloro $(- Cl)$ group has negative inductive effect $(- {NO}_{2}$ having more than $- Cl)$ and thus they pull electron density from phenolate original image ring making release of proton easier and the compound more acidic. On the other hand methyl $(- {CH}_{3})$ group has positive inductive effect making cresol less acidic. Their order of acidity is

JCECE - 2017

GENERAL ORGANIC CHEMISTRY

231471 Some meta-directing substituents in aromatic substituation are given. Which one is most deactivating?

1

- {SO}_{3} H

2

- CN

3

- COOH

4

- {NO}_{2}

Explanation:

Deactivating strength of meta-directing substituents (or electron with drawing group -EWG) decreases with decrease in $- I$ effect, which follows the order as
$R_{4} N^{\oplus} > - {NO}_{2} > - CN > - {SO}_{3} H > - COOH > - F > - Cl$ $> - I > - OR > - OH > - {NH}_{2} > - C_{6} H_{5}$

JCECE - 2017

GENERAL ORGANIC CHEMISTRY

231473 The most stable carbonium ion among the following is

1

C_{6} H_{5} - {CH}_{2} \overset{+}{C} H_{2}

2

{CH}_{3} - \overset{+}{C} H_{2}

3

C_{6} H_{5} - \overset{+}{C} - C_{6} H_{5}

4

C_{6} H_{5} \overset{+}{C} H_{2}

Explanation:

Delocalization and $+ I$ effect increase the stability of $+ I$ effect. Delocalization is dominating factor. Hence, the most stable carbocation or carbonium is- $C_{6} H_{5} - \overset{+}{C} - C_{6} H_{5}$ . Hence, (c) option is correct.
The order of stability is-
original image

JIPMER-2017

GENERAL ORGANIC CHEMISTRY

231468 Arrange the following in decreasing order of acidic strength.
(i) Benzoic acid
(ii) 4-nitrobenzoic acid
(iii) 3, 4-dinitrobenzoic acid
(iv) 4-methoxy benzoic acid

1 III

>

II

>

I

>

IV

2 III

>

II

>

IV

>

I

3 II

>

III

>

IV

>

I

4 I

>

II

>

III

>

IV

Explanation:

Since, electron donating groups decrease the acid strength, therefore, 4-methoxy benzoic acid is a weaker acid than benzoic acid. Further, since electronwithdrawing groups increase the acid strength, therefore, both 4-nitrobenzoic acid and 3, 4dinitrobenzoic acid are stronger acid than benzoic acid. Further, due to presence of an additional ${NO}_{2}$ at $m$ position with respect to $COOH$ group, 3, 4dinitrobenzoic acid is a little stronger acid than 4- nitrobenzoic acid thus the overall acid strength increase in the order:
4-methoxy benzoic acid $<$ benzoic acid $<$ 4 - nitrobenzoic acid $< 3$ , 4-dinitrobenzoic acid.

JCECE - 2016

GENERAL ORGANIC CHEMISTRY

231470 Among the following which is least acidic?

1 Phenol

2 o-cresol

3 p-nitrophenol

4 p-chlorophenol

Explanation:

Nitro $(- {NO}_{2})$ and chloro $(- Cl)$ group has negative inductive effect $(- {NO}_{2}$ having more than $- Cl)$ and thus they pull electron density from phenolate original image ring making release of proton easier and the compound more acidic. On the other hand methyl $(- {CH}_{3})$ group has positive inductive effect making cresol less acidic. Their order of acidity is

JCECE - 2017

GENERAL ORGANIC CHEMISTRY

231471 Some meta-directing substituents in aromatic substituation are given. Which one is most deactivating?

1

- {SO}_{3} H

2

- CN

3

- COOH

4

- {NO}_{2}

Explanation:

Deactivating strength of meta-directing substituents (or electron with drawing group -EWG) decreases with decrease in $- I$ effect, which follows the order as
$R_{4} N^{\oplus} > - {NO}_{2} > - CN > - {SO}_{3} H > - COOH > - F > - Cl$ $> - I > - OR > - OH > - {NH}_{2} > - C_{6} H_{5}$

JCECE - 2017

GENERAL ORGANIC CHEMISTRY

231473 The most stable carbonium ion among the following is

1

C_{6} H_{5} - {CH}_{2} \overset{+}{C} H_{2}

2

{CH}_{3} - \overset{+}{C} H_{2}

3

C_{6} H_{5} - \overset{+}{C} - C_{6} H_{5}

4

C_{6} H_{5} \overset{+}{C} H_{2}

Explanation:

Delocalization and $+ I$ effect increase the stability of $+ I$ effect. Delocalization is dominating factor. Hence, the most stable carbocation or carbonium is- $C_{6} H_{5} - \overset{+}{C} - C_{6} H_{5}$ . Hence, (c) option is correct.
The order of stability is-
original image

JIPMER-2017

GENERAL ORGANIC CHEMISTRY

231468 Arrange the following in decreasing order of acidic strength.
(i) Benzoic acid
(ii) 4-nitrobenzoic acid
(iii) 3, 4-dinitrobenzoic acid
(iv) 4-methoxy benzoic acid

1 III

>

II

>

I

>

IV

2 III

>

II

>

IV

>

I

3 II

>

III

>

IV

>

I

4 I

>

II

>

III

>

IV

Explanation:

Since, electron donating groups decrease the acid strength, therefore, 4-methoxy benzoic acid is a weaker acid than benzoic acid. Further, since electronwithdrawing groups increase the acid strength, therefore, both 4-nitrobenzoic acid and 3, 4dinitrobenzoic acid are stronger acid than benzoic acid. Further, due to presence of an additional ${NO}_{2}$ at $m$ position with respect to $COOH$ group, 3, 4dinitrobenzoic acid is a little stronger acid than 4- nitrobenzoic acid thus the overall acid strength increase in the order:
4-methoxy benzoic acid $<$ benzoic acid $<$ 4 - nitrobenzoic acid $< 3$ , 4-dinitrobenzoic acid.

JCECE - 2016

GENERAL ORGANIC CHEMISTRY

231470 Among the following which is least acidic?

1 Phenol

2 o-cresol

3 p-nitrophenol

4 p-chlorophenol

Explanation:

Nitro $(- {NO}_{2})$ and chloro $(- Cl)$ group has negative inductive effect $(- {NO}_{2}$ having more than $- Cl)$ and thus they pull electron density from phenolate original image ring making release of proton easier and the compound more acidic. On the other hand methyl $(- {CH}_{3})$ group has positive inductive effect making cresol less acidic. Their order of acidity is

JCECE - 2017

GENERAL ORGANIC CHEMISTRY

231471 Some meta-directing substituents in aromatic substituation are given. Which one is most deactivating?

1

- {SO}_{3} H

2

- CN

3

- COOH

4

- {NO}_{2}

Explanation:

Deactivating strength of meta-directing substituents (or electron with drawing group -EWG) decreases with decrease in $- I$ effect, which follows the order as
$R_{4} N^{\oplus} > - {NO}_{2} > - CN > - {SO}_{3} H > - COOH > - F > - Cl$ $> - I > - OR > - OH > - {NH}_{2} > - C_{6} H_{5}$

JCECE - 2017

GENERAL ORGANIC CHEMISTRY

231473 The most stable carbonium ion among the following is

1

C_{6} H_{5} - {CH}_{2} \overset{+}{C} H_{2}

2

{CH}_{3} - \overset{+}{C} H_{2}

3

C_{6} H_{5} - \overset{+}{C} - C_{6} H_{5}

4

C_{6} H_{5} \overset{+}{C} H_{2}

Explanation:

Delocalization and $+ I$ effect increase the stability of $+ I$ effect. Delocalization is dominating factor. Hence, the most stable carbocation or carbonium is- $C_{6} H_{5} - \overset{+}{C} - C_{6} H_{5}$ . Hence, (c) option is correct.
The order of stability is-
original image

JIPMER-2017

GENERAL ORGANIC CHEMISTRY

231468 Arrange the following in decreasing order of acidic strength.
(i) Benzoic acid
(ii) 4-nitrobenzoic acid
(iii) 3, 4-dinitrobenzoic acid
(iv) 4-methoxy benzoic acid

1 III

>

II

>

I

>

IV

2 III

>

II

>

IV

>

I

3 II

>

III

>

IV

>

I

4 I

>

II

>

III

>

IV

Explanation:

Since, electron donating groups decrease the acid strength, therefore, 4-methoxy benzoic acid is a weaker acid than benzoic acid. Further, since electronwithdrawing groups increase the acid strength, therefore, both 4-nitrobenzoic acid and 3, 4dinitrobenzoic acid are stronger acid than benzoic acid. Further, due to presence of an additional ${NO}_{2}$ at $m$ position with respect to $COOH$ group, 3, 4dinitrobenzoic acid is a little stronger acid than 4- nitrobenzoic acid thus the overall acid strength increase in the order:
4-methoxy benzoic acid $<$ benzoic acid $<$ 4 - nitrobenzoic acid $< 3$ , 4-dinitrobenzoic acid.

JCECE - 2016

GENERAL ORGANIC CHEMISTRY

231470 Among the following which is least acidic?

1 Phenol

2 o-cresol

3 p-nitrophenol

4 p-chlorophenol

Explanation:

Nitro $(- {NO}_{2})$ and chloro $(- Cl)$ group has negative inductive effect $(- {NO}_{2}$ having more than $- Cl)$ and thus they pull electron density from phenolate original image ring making release of proton easier and the compound more acidic. On the other hand methyl $(- {CH}_{3})$ group has positive inductive effect making cresol less acidic. Their order of acidity is

JCECE - 2017

GENERAL ORGANIC CHEMISTRY

231471 Some meta-directing substituents in aromatic substituation are given. Which one is most deactivating?

1

- {SO}_{3} H

2

- CN

3

- COOH

4

- {NO}_{2}

Explanation:

Deactivating strength of meta-directing substituents (or electron with drawing group -EWG) decreases with decrease in $- I$ effect, which follows the order as
$R_{4} N^{\oplus} > - {NO}_{2} > - CN > - {SO}_{3} H > - COOH > - F > - Cl$ $> - I > - OR > - OH > - {NH}_{2} > - C_{6} H_{5}$

JCECE - 2017

GENERAL ORGANIC CHEMISTRY

231473 The most stable carbonium ion among the following is

1

C_{6} H_{5} - {CH}_{2} \overset{+}{C} H_{2}

2

{CH}_{3} - \overset{+}{C} H_{2}

3

C_{6} H_{5} - \overset{+}{C} - C_{6} H_{5}

4

C_{6} H_{5} \overset{+}{C} H_{2}

Explanation:

Delocalization and $+ I$ effect increase the stability of $+ I$ effect. Delocalization is dominating factor. Hence, the most stable carbocation or carbonium is- $C_{6} H_{5} - \overset{+}{C} - C_{6} H_{5}$ . Hence, (c) option is correct.
The order of stability is-
original image

JIPMER-2017