CUET UG Chemistry Booster Test -3 Carboxylic Acids (Structure, Properties, Reactions & Uses)

Clemmensen reduction converts aldehydes and ketones into hydrocarbons using zinc-amalgam [Zn(Hg)] and concentrated hydrochloric acid. Since the reaction medium is strongly acidic, compounds containing acid-sensitive functional groups may undergo unwanted side reactions or decomposition. Therefore, Clemmensen reduction is unsuitable for acid-sensitive substrates.

List-I — Correct Match Clemmensen reduction — Concentrated HCl and Zn(Hg) Wolff-Kishner reduction — Hydrazine + KOH in ethylene glycol Catalytic hydrogenation — H₂ with metal catalyst Hydrazone formation — Intermediate step in Wolff-Kishner Thus: 1-a, 2-b, 3-c, 4-d

In Tollens' test, aldehydes are oxidised to carboxylate ions while silver ions are reduced to metallic silver, producing a characteristic silver mirror. Correct statements: ✔ Uses ammoniacal silver nitrate. ✔ Produces a silver mirror. ✔ Occurs in alkaline medium. Statement 3 is incorrect because aldehydes are oxidised, not reduced.

Fehling's reagent is prepared by mixing: Fehling Solution A: Aqueous copper sulphate Fehling Solution B: Alkaline sodium potassium tartrate (Rochelle salt) The tartrate ion helps keep copper(II) ions in solution under alkaline conditions.

The haloform reaction is characteristic of compounds containing the CH₃CO– group. Sodium hypohalite converts the methyl group attached to the carbonyl carbon into a haloform (CHX₃), while the remaining fragment becomes a carboxylate salt. In this reaction, the carbon-carbon double bond remains unaffected, while the methyl ketone group undergoes haloform oxidation.

In the haloform reaction, sodium hypohalite selectively oxidizes the methyl ketone group (–COCH₃). Even if a molecule contains a carbon-carbon double bond, the reaction primarily occurs at the methyl ketone functionality and does not affect the double bond. For example, 4-methylpent-3-en-2-one undergoes haloform oxidation to give a carboxylate salt and a haloform while retaining its C=C bond.

The electrophilicity of the carbonyl carbon decreases as electron-donating alkyl groups increase. Order: Ethanal > Propanal > Propanone > Butanone Reason: Aldehydes have only one alkyl group. Ketones have two alkyl groups, reducing electrophilicity through +I effect. Larger alkyl groups further decrease electrophilicity and increase steric hindrance.

When a base removes an α-hydrogen from an aldehyde or ketone, an enolate ion is produced. The negative charge is delocalized between the α-carbon and the oxygen atom through resonance. This resonance stabilization makes α-hydrogens significantly more acidic and easier to remove than β- or γ-hydrogens.

In aldol addition, two molecules of an aldehyde (or ketone) participate: 1. One molecule forms an enolate ion. 2. The enolate attacks the carbonyl carbon of a second molecule. Thus, two aldehyde molecules combine to produce one aldol product. Example: 2 CH₃CHO → CH₃CH(OH)CH₂CHO (3-Hydroxybutanal)

Aldol addition of ethanal gives: 3-Hydroxybutanal Upon heating, dehydration occurs: CH₃CH(OH)CH₂CHO → CH₃CH=CHCHO + H₂O The product is But-2-enal (Crotonaldehyde).

Cross aldol condensation is carried out between two different carbonyl compounds, which may be aldehydes, ketones, or one of each. Ketones that possess α-hydrogens can form enolate ions and participate effectively in the reaction. Example: Acetophenone and benzaldehyde undergo cross aldol condensation, where acetophenone forms the enolate ion.

When ethanal and propanal are mixed in dilute alkali: Both aldehydes possess α-hydrogens. Each can undergo self-condensation. Each can react with the other to give cross-condensation products. Therefore, a mixture of four aldol products may be obtained: 1. Self-aldol of ethanal 2. Self-aldol of propanal 3. Cross product (ethanal enolate + propanal) 4. Cross product (propanal enolate + ethanal) Hence statements A, B and C are correct.

In the Cannizzaro reaction: [ 2C_6H_5CHO + OH^- \rightarrow C_6H_5CH_2OH + C_6H_5COO^- ] One benzaldehyde molecule is reduced to benzyl alcohol, whose IUPAC name is phenylmethanol.

Formaldehyde undergoes the Cannizzaro reaction in concentrated alkali. 2HCHO + NaOH CH_3OH + HCOONa One molecule is: Oxidized to sodium formate. Another molecule is: Reduced to methanol. Since oxidation and reduction occur simultaneously among identical molecules, it is a disproportionation reaction.

List-I — List-II 1. Benzaldehyde — a. Gives meta-substituted products 2. Acetophenone — b. Acts as a methyl ketone in haloform reaction 3. Benzene — c. Undergoes Friedel-Crafts acylation easily to form ketones 4. Toluene — d. Can be oxidised to benzaldehyde using chromyl chloride Therefore: 1-a, 2-b, 3-c, 4-d

The carbonyl group (–CHO) withdraws electron density from the benzene ring through both inductive (–I) and resonance (–M) effects. As a result, the ortho and para positions become relatively electron deficient, making meta substitution more favorable. Thus, nitration of benzaldehyde proceeds through electrophilic aromatic substitution, yielding predominantly meta-nitrobenzaldehyde.

Urea-formaldehyde glue is a polymeric resin formed by the condensation reaction between urea and formaldehyde (methanal). The resulting resin possesses excellent adhesive properties and is extensively used in plywood, particle boards, and laminates.

Acetaldehyde (ethanal) is widely used as a starting material in the preparation of: Acetic acid Ethyl acetate Vinyl acetate Various polymers Pharmaceutical intermediates Therefore, acetaldehyde is the correct answer.

The passage clearly states that methanal is a gas at room temperature, whereas ethanal is a volatile liquid and higher aldehydes and ketones are liquids or solids. Because of its low molecular mass and weak intermolecular forces, methanal remains gaseous under ordinary conditions.

The carbonyl group (C=O) is highly polar because oxygen is more electronegative than carbon. This polarity gives rise to dipole-dipole intermolecular attractions between aldehyde and ketone molecules. These interactions are stronger than the forces present in hydrocarbons and ethers of similar molecular masses, resulting in higher boiling points. However, aldehydes and ketones have lower boiling points than alcohols because they cannot form intermolecular hydrogen bonds among themselves.