Question

Column-I Column-II (Pair of compounds) (Can be distinguished by) (A) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}\) and \(\mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH}\) (P) \(\mathrm{NaNH}_{2}\) (B) \(\mathrm{CH}_{3}-\mathrm{CH}_{3}\) and \(\mathrm{CH}_{3}-\mathrm{CH} \equiv \mathrm{CH}\) (Q) \(\mathrm{Br}_{2} / \mathrm{H}_{2} \mathrm{O}\) (C) \(\mathrm{CH}_{3} \mathrm{COOH}\) and \(\mathrm{CH}_{3}-\mathrm{CH}(\mathrm{OH})-\mathrm{CH}_{3}\) (R) Aq. \(\mathrm{NaHCO}_{3}\) (D) \(\mathrm{CH}_{3}-\mathrm{OH}\) and \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}\) (S) Na metal (T) Aq. \(\mathrm{NaOH}\)

Short answer

The short answer based on the step-by-step solution is: (A) - (Q) (B) - (S) (C) - (R) (D) - (T)

Step-by-step solution

Identify the functional groups in the compounds

Here are the functional groups in each pair of compounds: (A) Alkene and alkyne (B) Alkane and alkyne (C) Carboxylic acid and secondary alcohol (D) Alcohol and alkene ##Step 2: Matching reactions to distinguish each pair## For each of the compound pairs, we will determine which reaction can help us in distinguishing them.

(A): \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}\) and \(\mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH}\)

Alkenes undergo addition reactions with halogens, whereas alkynes undergo only halogenation in dark. Therefore, \(\mathrm{Br}_{2}/\mathrm{H}_{2}\mathrm{O}\) (Q) can be used to distinguish these two compounds.

(B): \(\mathrm{CH}_{3}-\mathrm{CH}_{3}\) and \(\mathrm{CH}_{3}-\mathrm{CH} \equiv \mathrm{CH}\)

Alkynes react with sodium metal to form acetylide salts, whereas alkanes do not react. Thus, Na metal (S) can be used to distinguish these two compounds.

(C): \(\mathrm{CH}_{3} \mathrm{COOH}\) and \(\mathrm{CH}_{3}-\mathrm{CH}(\mathrm{OH})-\mathrm{CH}_{3}\)

Carboxylic acids react with Aq. \(\mathrm{NaHCO}_{3}\) to release carbon dioxide, whereas alcohols do not. Therefore, Aq. \(\mathrm{NaHCO}_{3}\) (R) can be used to distinguish these two compounds.

(D): \(\mathrm{CH}_{3}-\mathrm{OH}\) and \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}\)

Alcohols can be deprotonated by strong bases to form alkoxide ions, whereas alkenes do not react under the same conditions. Thus, Aq. \(\mathrm{NaOH}\) (T) can be used to distinguish these two compounds. #Final answer: (A) - (Q) (B) - (S) (C) - (R) (D) - (T)

Key concepts

Alkenes and Alkynes

Alkenes and alkynes are fundamental classes of hydrocarbons that are characterized by their carbon-carbon multiple bonds. Alkenes contain at least one carbon-carbon double bond \(>C=C<\), while alkynes possess at least one carbon-carbon triple bond \(\equiv\). This difference in bonding not only affects their chemical properties but also how they react with other substances.
Alkenes are prone to addition reactions, where compounds like halogens can add across the double bond. This property is commonly used in chemical tests for alkenes. For instance, when bromine water \(\text{Br}_2/\text{H}_2\text{O}\) is added to an alkene, the solution undergoes a color change from brown to colorless, indicating the presence of the unsaturated bond.
In contrast, alkynes, with their triple bonds, react differently. They can undergo similar halogenation reactions, but under specific conditions, such as darkness, allowing them to be distinguished from alkenes. Additionally, alkynes can react with strong bases such as sodium amide (\(\text{NaNH}_2\)), forming acetylide ions, another distinguishing reaction from alkenes.

Reaction Mechanisms

Understanding reaction mechanisms is crucial in the identification and differentiation of various organic compounds. Reaction mechanisms describe the step-by-step process by which chemical reactions occur, detailing the breaking and forming of bonds.

While determining the reactions suitable for distinguishing compound pairs, we rely on specific distinctive reactions. Alkenes, for example, undergo electrophilic addition reactions where the double bond acts as a nucleophile. This makes it reactive towards electrophiles like bromine.

• Alkynes can undergo similar reactions but with slower kinetics and different conditions because of their more robust triple bonds.
• Compounds like carboxylic acids undergo reactions such as neutralization with bases, releasing gas as a byproduct which is easy to observe.

This understanding of how each functional group interacts in reaction mechanisms allows chemists to carry out deliberate tests that help differentiate between compound types.

Organic Compound Differentiation

Differentiating organic compounds involves identifying characteristic functional groups and utilizing specific reactions that highlight these differences. Functional groups give organic molecules their unique chemical reactivity and can include alkenes, alkynes, alcohols, carboxylic acids, and more.
For example, distinguishing alkenes from alkynes can be achieved through tests like the bromine water test. Meanwhile, alcohols can be identified based on their reactions with strong bases, forming alkoxides, which is not possible with alkenes.

• Carboxylic acids are easily differentiated from alcohols by their reaction with bicarbonates, producing carbon dioxide gas, a clear confirmatory reaction.
• In another respect, distinguishing alkanes from alkynes can be carried out using metallic sodium. Here, alkynes form acetylide salts upon reaction, making them stand out.

These chemically intricate differences make organic compound differentiation both a fascinating and informative process, opening the door to a deeper understanding of organic chemistry and its applications.