Aldehydes And Ketones MCQ Quiz in मल्याळम - Objective Question with Answer for Aldehydes And Ketones - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

CONCEPT:

Hydrolysis of Acid Chlorides

• Acid chlorides are organic compounds containing the functional group –COCl. They undergo hydrolysis when reacted with water, breaking down into the corresponding carboxylic acid and releasing hydrochloric acid (HCl).
• The rate of hydrolysis of acid chlorides is affected by the electron-withdrawing or electron-donating effects of substituents on the aromatic ring or alkyl group attached to the carbonyl group.
• Electron-withdrawing groups (like –NO₂, –CN, etc.) increase the electrophilicity of the carbonyl carbon, making it more susceptible to nucleophilic attack by water, thus increasing the rate of hydrolysis.
• Electron-donating groups (like –OH, –OCH₃, etc.) decrease the electrophilicity of the carbonyl carbon, making the hydrolysis reaction slower.

EXPLANATION:

•  
  • (A) C₆H₅CHOCOCl: The –CHO group is an electron-withdrawing group, but it does not directly affect the carbonyl carbon in a way that greatly enhances hydrolysis. This compound will hydrolyze more slowly compared to others. 
  • (B) C₆H₅OHCOCl: ​The hydroxyl group is an electron-donating group, which will reduce the electrophilicity of the carbonyl carbon and slow down the hydrolysis reaction
  • (C) C₆H₅COCl with a –NO₂ group attached to the ring: The nitro group is a strong electron-withdrawing group and will increase the electrophilicity of the carbonyl carbon, thereby increasing the hydrolysis rate.
  • (D) C₆H₅COCl with no group attached to the ring: It has no electron-donating or strongly electron-withdrawing groups attached to the ring. Its hydrolysis will proceed at a moderate rate.
• Based on the electron-withdrawing or donating effects of the substituents, the order of increasing hydrolysis rates will be:
  • (B) < (D) < (A) < (C)

Therefore, the correct answer is: 2) (B) < (D) < (A) < (C)

CONCEPT:

Fehling's Test

• Fehling's test is used to detect the presence of reducing sugars and aldehydes.
• Compounds with an aldehyde group (-CHO) or α-hydroxy ketones give a positive Fehling's test, resulting in the formation of a red precipitate of cuprous oxide (Cu₂O).
• Ketones and aromatic aldehydes (like benzaldehyde) generally do not give a positive Fehling's test.

EXPLANATION:

• Compound (A): Benzaldehyde (C₆H₅CHO) is an aromatic aldehyde and does not give a positive Fehling's test.
• Compound (B): Acetophenone (C₆H₅COCH₃) is a ketone and does not give a positive Fehling's test.
• Compound (C): Glucose derivative (HOCH₂–CO–(CHOH)₃–CH₂OH) contains an α-hydroxy aldehyde functional group and gives a positive Fehling's test.
• Compound (D): Propionaldehyde (CH₃CH₂CHO) is an aliphatic aldehyde and gives a positive Fehling's test.
• Compound (E): Phenylacetaldehyde (C₆H₅CH₂CHO) is an aliphatic aldehyde and gives a positive Fehling's test.

Therefore, the compounds (C), (D), and (E) give a positive Fehling's test.

Concept

Explanation:

CONCEPT:

Rate of Nucleophilic Addition Reactions (NAR) in Carbonyl Compounds

• The rate of nucleophilic addition reactions in carbonyl compounds depends on the electron-withdrawing or electron-donating effects of substituents attached to the carbonyl carbon.
• Electron-withdrawing groups increase the partial positive charge on the carbonyl carbon, making it more electrophilic and thus more susceptible to nucleophilic attack.
• Electron-donating groups decrease the electrophilicity of the carbonyl carbon, thereby reducing the rate of nucleophilic addition reactions.

CALCULATION:

• Compound I (Formaldehyde, HCHO): No alkyl or electron-donating groups are present, so the carbonyl carbon is highly electrophilic. This makes formaldehyde the most reactive toward nucleophilic addition.
• Compound II (Acetaldehyde, CH₃CHO): Contains one electron-donating methyl group, which slightly decreases the electrophilicity of the carbonyl carbon, making it less reactive than formaldehyde.
• Compound III (p-Nitrobenzaldehyde, C₆H₄(NO₂)CHO): Contains an electron-withdrawing nitro group (-NO₂) in the para position, which increases the electrophilicity of the carbonyl carbon. However, its effect is weaker compared to formaldehyde and acetaldehyde.
• Compound IV (p-Tolualdehyde, C₆H₄(CH₃)CHO): Contains an electron-donating methyl group (-CH₃) in the para position, which decreases the electrophilicity of the carbonyl carbon, making it the least reactive toward nucleophilic addition.

CONCLUSION:

The correct option is: Option 1

CONCEPT:

Reduction of Aldehydes to Alcohols

• Aldehydes, like benzaldehyde, can be reduced to primary alcohols (such as benzyl alcohol) using specific reducing agents.
• The choice of reducing agent depends on the reactivity and the type of reduction required.

EXPLANATION:

• NaBH₄ (Sodium borohydride) — NaBH₄ is a mild reducing agent commonly used to reduce aldehydes and ketones to their corresponding alcohols. It selectively reduces benzaldehyde to benzyl alcohol. 
• 
• Zinc dust acts as a reducing agent. Phenol undergoes reduction reaction in presence of zinc dust. Reduction reaction means the addition of electrons or removal of oxygen or addition of hydrogen.
• Zn/Hg with HCl (Clemmensen reduction) — This reagent is used for the reduction of ketones and aldehydes to alkanes, not alcohols.
• Cu/H₂SO₄ — This reagent is not commonly used for the reduction of aldehydes to alcohols and is more involved in oxidation or other types of reactions.

CONCLUSION:

• NaBH₄ is the reagent used to reduce benzaldehyde to benzyl alcohol.

Explanation:

• Aromaticity is defined as a property of the conjugated cycloalkenes which enhances the stability of a molecule due to the delocalization of electrons present in the π-π orbitals.
• Aromatic molecules are said to be very stable, and they do not break so easily and also react with other types of substances. The organic compounds which are not said to be aromatic are known as aliphatic compounds. These might be in cyclic form, but only the aromatic rings have a special kind of stability.
• Aromaticity is the key factor in deciding maximum enolization in the given compound.
• Since aromatic compounds are more stable than any saturated /unsaturated(aliphatic). thus maximum enolization takes place in the aromatic compound.

So option 2 is the correct answer.

Explanation-

Claisen condensation-

The Claisen condensation reaction is an organic coupling reaction that results in the formation of a C-C bond between either a single ester and one carbonyl compound or between two esters.

The reaction proceeds when a strong base is present and the product of the reaction is a beta-keto ester or a beta-diketone.

The mechanism of the Claisen condensation reaction proceeds with the removal of an alpha proton through the action of a strong base to result in the formation of an enolate ion.

Given reaction and analysis-

The compound (A) can form oxime on reaction with NH₂​OH.

Since the molecule can involve simple proton transfer in an intramolecular fashion, it can undergo tautomerism, as it has alpha hydrogen present in it.

Iodoform test is used to prove the presence of methyl ketone.  Since there is a methyl ketone it shows the iodoform test.  

So all the statements are true.

CONCEPT:

Sequential Reactions: Reduction, Oxidation, and Nucleophilic Addition

• The given reaction involves multiple steps, including reduction, oxidation, and nucleophilic addition reactions.
• Step 1: Lithium aluminium hydride (LiAlH₄) is a strong reducing agent that reduces carboxylic acids to primary alcohols.
• Step 2: PCC (Pyridinium chlorochromate) is an oxidizing agent that converts primary alcohols to aldehydes.
• Step 3: HCN/NaOH results in the nucleophilic addition of cyanide to the aldehyde, forming a cyanohydrin.
• Step 4: Hydrolysis of the cyanohydrin in the presence of heat and base (H₂O/NaOH) converts the cyano group to a carboxyl group.

EXPLANATION:

• Starting with acetic acid (CH₃-COOH):
  • Reduction by LiAlH₄ forms ethanol (CH₃-CH₂-OH).
  • Oxidation by PCC converts the ethanol into acetaldehyde (CH₃-CHO).
  • Addition of HCN leads to the formation of a cyanohydrin (CH₃-CH(OH)-CN).
  • Hydrolysis of the cyanohydrin forms lactic acid (CH₃-CH(OH)-COOH).
• The major product P is lactic acid (CH₃-CH(OH)-COOH), which corresponds to option (4).

Conclusion:-

• The major product P is lactic acid (CH₃-CH(OH)-COOH), as shown in option (4).