Basics of Organic Chemistry (GOC) — Page 9 | JEE Chemistry

Q81

Given below are two statements : Statement I : Tropolone is an aromatic compound and has

8 \pi

electrons. Statement II :

\pi

electrons of

> \mathrm{C}=\mathrm{O}

group in tropolone is involved in aromaticity. 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 Both Statement I and Statement II are false

C Statement I is true but Statement II is false

D Both Statement I and Statement II are true

Correct Answer

Option B

Solution

Let's analyze the structure of tropolone to evaluate the given statements.

1.

Statement I: "Tropolone is an aromatic compound and has

8 \pi

electrons."

Tropolone is a seven-membered ring compound with an oxygen atom attached to it through a double bond, creating a carbonyl group (C=O).

To determine if it is aromatic, we should check if it meets Hückel's rule for aromaticity, which states that a molecule is aromatic if it is cyclic, planar, and has a

4n + 2

$\pi$ electrons (where n is a non-negative integer).

Upon examining the structure of tropolone: Electrons Count Electrons from double bonds in the ring 6 Electrons from the carbonyl $\pi$ bond 2 Total $\pi$ electrons 8 According to the table, tropolone has a total of 8 $\pi$ electrons.

Since 8 does not satisfy the

4n + 2

rule (where n would be 1 or 2, leading to 6 or 10 $\pi$ electrons), tropolone does not qualify as aromatic.

Therefore, Statement I is false.

2.

Statement II: " $\pi$ electrons of

> \mathrm{C}=\mathrm{O}

group in tropolone is involved in aromaticity."

As established, tropolone does not meet the criteria for aromaticity.

Additionally, the $\pi$ electrons of the carbonyl group indeed contribute to the total count of $\pi$ electrons in the ring system, but since tropolone isn't aromatic, Statement II is false.

Given the analysis, the correct answer is: Option B: Both Statement I and Statement II are false

Q82

The correct decreasing order of priority for the functional groups of organic compounds in the IUPAC system of nomenclature is

A −COOH, −SO3H, −CONH2, −CHO

B −SO3H, −COOH, −CONH2, −CHO

C −CHO, −COOH, −SO3H, −CONH2

D −CONH2, −CHO, −SO3H, −COOH

Correct Answer

Option A

Solution

The correct order of priority for the given functional group is .tg .tg Functional group (priority order) suffix(s) prefix (1) Oic acid(when carbon(C) of this functional group present in the main chain) or Carboxylic acid (when carbon(C) of this functional group is not present in the main chain) Carboxy (2) sulphonic acid sulpho (3) Oic anhydrid (when carbon(C) of this functional group present in the main chain) or Carboxylic anhydride (when carbon(C) of this functional group is not present in the main chain) $-$ (4) Oate (when carbon(C) of this functional group present in the main chain) or Carboxylate (when carbon(C) of this functional group is not present in the main chain) $-$ (5) Oyl halide (when carbon(C) of this functional group present in the main chain) or Carboxyl halide (when carbon(C) of this functional group is not present in the main chain) haloflormyl (6) amide (when carbon(C) of this functional group present in the main chain) or carbamide (when carbon(C) of this functional group is not present in the main chain) carbamoyl (7) cynide ( $-$ C $\equiv$ N) nitrile (when carbon(C) of this functional group present in the main chain) or carbonitrile (when carbon(C) of this functional group is not present in the main chain) cyano (8) Carbylamine isocyano (9) al (when carbon(C) of this functional group present in the main chain) or Carbaldehyde (when carbon(C) of this functional group is not present in the main chain) formyl (oxo) (10) one oxo (11) $-$ OH ol hydroxy (12) $-$ SH thiol mercapto (13) $-$ NH

_2

amine amino From this table you can see -COOH has highest priority and -NH2 has lowest priority among all functional groups.

Q83

Match List I with List II: .tg .tg List I (Mixture) List II (Separation Technique) A.

\mathrm{CHCl}_3+\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2

I. Steam distillation B.

\mathrm{C}_6 \mathrm{H}_{14}+\mathrm{C}_5 \mathrm{H}_{12}

II. Differential extraction C.

\mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2+\mathrm{H}_2 \mathrm{O}

III. Distillation D.

\text{ Organic compound in } \mathrm{H}_2 \mathrm{O}

IV. Fractional distillation

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

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

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

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

Correct Answer

Option D

Solution

.tg .tg Mixture Separation technique (A)

\mathrm{CHCl_3+C_6H_5NH_2}

$\to$ Distillation (B)

\mathrm{C_6H_4+C_5H_{12}}

$\to$ Fractional distillation (C)

{C_6H_NH_2+H_2O}

$\to$ Steam distillation (D) Organic compound in

\mathrm{H_2O}

$\to$ Differential extraction

Q84

The correct sequence of acidic strength of the following aliphatic acids in their decreasing order is:

\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{COOH}, \mathrm{CH}_3 \mathrm{COOH}, \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COOH}, \mathrm{HCOOH}

A

\mathrm{HCOOH}>\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COOH}>\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{COOH}>\mathrm{CH}_3 \mathrm{COOH}

B

\mathrm{HCOOH}>\mathrm{CH}_3 \mathrm{COOH}>\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{COOH}>\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COOH}

C

\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COOH}>\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{COOH}>\mathrm{CH}_3 \mathrm{COOH}>\mathrm{HCOOH}

D

\mathrm{CH}_3 \mathrm{COOH}>\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{COOH}>\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COOH}>\mathrm{HCOOH}

Correct Answer

Option B

Solution

\begin{aligned} & \mathrm{HCOOH}>\mathrm{CH}_3 \mathrm{COOH}>\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{COOH}> \\ & \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COOH} \end{aligned}

Q85

Given below are two statements : Statement I : Retardation factor (Rf) can be measured in meter/centimeter. Statement II : Rf value of a compound remains constant in all solvents. Choose the most appropriate answer from the options given below :

A Statement I is true but statement II is false

B Statement I is false but statement II is true

C Both statement I and statement II are true

D Both statement I and statement II are false

Correct Answer

Option D

Solution

Retardation factor (Rf) is the ratio of the distance moved by the substance from the baseline to the distance moved by the solvent from the baseline.

So, it is dimensionless.

The distance moved by the substance is due to the adsorption of the substance on the stationary phase.

It does not depend on the nature of the solvent.

But the distance moved by the solvent will change with the nature of the solvent.

Therefore, Rf will vary with the change in the solvent.

So, both the statements are false.

Q86

Phenol on reaction with dilute nitric acid, gives two products. Which method will be most efficient for large scale separation?

A Chromatographic separation

B Fractional Crystallisation

C Steam distillation

D Sublimation

Correct Answer

Option C

Solution

o-Nitrophenol and p-Nitrophenol can be easily separated by steam distillation.

Q87

Which among the following is incorrect statement?

A The electromeric effect is, temporary effect

B Hydrogen ion

(\mathrm{H}^{+})

shows negative electromeric effect

C The organic compound shows electromeric effect in the presence of the reagent only.

D Electromeric effect dominates over inductive effect

Correct Answer

Option B

Solution

Let's analyze each statement to determine which is incorrect: Option A: The electromeric effect is a temporary effect.

This statement is correct.

The electromeric effect is indeed a temporary effect that occurs in the presence of a reagent and disappears when the reagent is removed.

Option B: Hydrogen ion

(\mathrm{H}^{+})

shows negative electromeric effect.

To understand this, let's define the electromeric effect.

The electromeric effect involves the transfer of electron pairs within a molecule in the presence of an attacking reagent.

There are two types of electromeric effects: the positive electromeric effect (

E^+

) and the negative electromeric effect (

E^-

).

A positive electromeric effect occurs when electrons are transferred towards the reagent, while a negative electromeric effect occurs when electrons are transferred away from the reagent.

Since a hydrogen ion

(\mathrm{H}^{+})

is an electron-deficient species (it lacks electrons), it would generally induce the transfer of electrons towards itself, resulting in a positive electromeric effect.

Hence, this statement is incorrect.

Option C: The organic compound shows electromeric effect in the presence of the reagent only.

This statement is correct.

The electromeric effect is observed only in the presence of an attacking reagent.

Once the reagent is removed, the effect ceases to exist.

Option D: Electromeric effect dominates over inductive effect.

This statement is correct.

The electromeric effect generally has a stronger influence on the electronic distribution within a molecule compared to the inductive effect, especially when both effects are present simultaneously.

Therefore, the incorrect statement is: Option B: Hydrogen ion

(\mathrm{H}^{+})

shows negative electromeric effect.