Basics of Organic Chemistry (GOC) Questions — NEET Chemistry

Q1

\text{ The correct IUPAC name of the following compound is : }

A 3-ethyl-5-methylheptane

B 2,4-diethylhexane

C 3-methyl-5-ethylheptane

D 3,5-diethylhexane

Correct Answer

Option A

Solution

IUPAC name : 3-ethyl-5-methylheptane Numbering of parent chain should follow lowest locant rule.

Prefixes should be written in alphabetical order.

Q2

During Lassaigne's test, the elements present in an organic compound are converted from :

A Ionic form to ionic form

B Covalent form to ionic form

C Covalent form to covalent form

D Ionic form to covalent form

Correct Answer

Option B

Solution

In Lassaigne's test, the elements present in an organic compound are converted from covalent form to ionic form .

So, the correct answer is: Option B: Covalent form to ionic form Reason: In organic compounds, elements like nitrogen, sulphur, and halogens are usually present in the covalent state .

Since covalent compounds do not give the usual ionic reactions directly, the compound is fused with sodium.

This converts these elements into ionic sodium salts , such as:

\text{NaCN, Na}_2\text{S, NaX}

These ionic forms can then be easily tested. Therefore, the answer is:

\boxed{\text{Covalent form to ionic form}}

Q3

How many products (including stereoisomers) are expected from monochlorination of the following compound?

A 5

B 6

C 2

D 3

Correct Answer

Option B

Solution

Possible monochlorination products: Total 6 isomers.

Q4

Total number of possible isomers (both structural as well as stereoisomers) of cyclic ethers of molecular formula

\mathrm{C}_4 \mathrm{H}_8 \mathrm{O}

is :

A 10

B 11

C 6

D 8

Correct Answer

Option A

Solution

For cyclic ethers O should be in ring * carbon here is chiral Total number of isomers $=2+1+1+1+2+1+2=10$

Q5

Among the given compounds I-III, the correct order of bond dissociation energy of C-H bond marked with * is :

A III

>

II

>

I

B II

>

III

>

I

C II

>

I

>

III

D I

>

II

>

III

Correct Answer

Option C

Solution

I. carbon of this bond is sp $^2$ hybridised II. carbon of this bond is sp hybridised III. carbon of this bond is sp $^3$ hybridised Higher the percentage s character, stronger is C-H bond.

Correct order of bond dissociation energy of C-H bond:

II > I > III

Q6

Which one of the following compounds can exist as cis-trans isomers?

A 1, 1-Dimethylcyclopropane

B 1, 2-Dimethylcyclohexane

C Pent-1-ene

D 2-Methylhex-2-ene

Correct Answer

Option B

Solution

Cis-trans isomers shown by: Condition: Restricted rotation around double bond Or Different group around double bond

Q7

The correct IUPAC name of the compound is :

A 4-ethyl-1-fluoro-2-nitrobenzene

B 4-ethyl-1-fluoro-6-nitrobenzene

C 3-ethyl-6-fluoro-1-nitrobenzene

D 1-ethyl-4-fluoro-3-nitrobenzene

Correct Answer

Option A

Solution

\text{ 4-ethyl-1-fluoro-2-nitrobenzene }

Q8

A steam volatile organic compound which is immiscible with water has a boiling point of

250^{\circ} \mathrm{C}

. During steam distillation, a mixture of this organic compound and water will boil :

A above

100^{\circ} \mathrm{C}

but below

250^{\circ} \mathrm{C}

B above

250^{\circ} \mathrm{C}

C at

250^{\circ} \mathrm{C}

D close to but below

100^{\circ} \mathrm{C}

Correct Answer

Option D

Solution

Steam distillation is a separation technique used for purifying organic compounds that are immiscible with water and have high boiling points.

In this method, the organic compound co-distills with water.

The key concept here is that the total vapor pressure of the mixture is the sum of the vapor pressures of the organic compound and water.

When the total vapor pressure equals atmospheric pressure, the mixture will boil.

For a compound that has a boiling point of

250^{\circ} \mathrm{C}

and is immiscible with water, during steam distillation, the boiling point of the mixture will be influenced by both the vapor pressure of water and the organic compound.

Since water has a boiling point of

100^{\circ} \mathrm{C}

, steam distillation allows the mixture to boil at a temperature lower than the boiling point of the organic compound when in pure form.

This is because the partial pressures of both the water and the organic compound add up to reach the atmospheric pressure more quickly than either would alone.

Practically, the mixture will boil at a temperature close to the boiling point of water, which is

100^{\circ} \mathrm{C}

. Hence, the correct answer is: Option D close to but below

100^{\circ} \mathrm{C}

Q9

Methyl group attached to a positively charged carbon atom stabilizes the carbocation due to

A –I inductive effect

B electromeric effect

C hyperconjugation

D mesomeric effect

Correct Answer

Option C

Solution

Methyl group attached to a positively charged carbon atom stabilizes the carbocation due to hyperconjugation and +I effect.

Q10

On heating, some solid substances change from solid to vapour state without passing through liquid state. The technique used for the purification of such solid substances based on the above principle is known as

A Crystallization

B Sublimation

C Distillation

D Chromatography

Correct Answer

Option B

Solution

The technique described in the question is known as sublimation.

Sublimation is a process where a solid turns directly into a gas without passing through the intermediate liquid state.

This physical change occurs under specific conditions of temperature and pressure and is characteristic of certain substances.

Option B: Sublimation is the correct answer because it directly describes the process of solid substances transforming into vapour without becoming liquid first.

For example, substances like iodine, naphthalene, and dry ice (solid carbon dioxide) sublimate when heated under normal atmospheric conditions.

Sublimation is not only a fascinating chemical process but is also exploited in various scientific and industrial applications, including purification of substances, where impurities do not sublimate and can thus be easily separated from the vaporized material.

The other options provided do not describe this process: Crystallization (Option A) involves the formation of solid crystals from a homogeneous solution.

It is typically used to purify solids wherein the impurities remain dissolved in the solvent.

Distillation (Option C) is a process used to separate mixtures based on differences in the conditions required to change the phase (liquid phase) of the components of the mixture.

It does not involve direct transition from solid to gas.

Chromatography (Option D) is a method for separating components of a mixture based on differences in their movement through a stationary medium under the influence of a solvent or carrier gas.

It does not involve the phase transition of solid to gas directly.