Structure and uses of benzaldehyde MCQs With Answer

Structure and uses of benzaldehyde MCQs With Answer
Benzaldehyde, an aromatic aldehyde (C6H5CHO), features a formyl group attached to a benzene ring and is central to many pharmaceutical syntheses. This introduction covers benzaldehyde structure, spectral identification (IR, 1H/13C NMR), chemical reactivity (oxidation to benzoic acid, reduction, Cannizzaro and benzoin condensations), laboratory syntheses and industrial uses in flavors, fragrances, intermediates and drug precursors. Emphasis on physicochemical properties, safety, solubility and reaction mechanisms will help B.Pharm students apply concepts in medicinal chemistry and pharmaceutics. Keywords: benzaldehyde structure, benzaldehyde uses in pharmacy, aromatic aldehyde, benzaldehyde MCQs, benzaldehyde properties. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the molecular formula of benzaldehyde?

• C6H6O
• C6H5CHO
• C7H6O2
• C6H5CH2OH

Correct Answer: C6H5CHO

Q2. Which functional group is present in benzaldehyde?

• Alcohol
• Ketone
• Aldehyde
• Carboxylic acid

Correct Answer: Aldehyde

Q3. What is the characteristic smell of benzaldehyde commonly described as?

• Vanilla-like
• Almond-like
• Citrus-like
• Floral

Correct Answer: Almond-like

Q4. Which reaction does benzaldehyde undergo readily because it lacks alpha hydrogen?

• Aldol condensation
• Cannizzaro reaction
• Claisen condensation
• Michael addition

Correct Answer: Cannizzaro reaction

Q5. In the Cannizzaro reaction of benzaldehyde under strong base, what are the products?

• Benzyl alcohol and benzoic acid
• Benzaldehyde dimer and water
• Benzyl chloride and sodium benzoate
• Benzoin and hydrogen peroxide

Correct Answer: Benzyl alcohol and benzoic acid

Q6. Which reagent is commonly used to oxidize benzaldehyde to benzoic acid in the lab?

• NaBH4
• KMnO4
• Cl2/FeCl3
• LiAlH4

Correct Answer: KMnO4

Q7. Which reducing agent converts benzaldehyde to benzyl alcohol selectively under mild conditions?

• NaBH4
• KMnO4
• H2/Pd (excess)
• O3

Correct Answer: NaBH4

Q8. In 1H NMR spectroscopy, approximately where does the aldehydic proton of benzaldehyde appear?

• 0.9–1.5 ppm
• 3.5–4.5 ppm
• 7.0–8.0 ppm
• 9.5–10.0 ppm

Correct Answer: 9.5–10.0 ppm

Q9. Which IR absorption band is characteristic of the carbonyl (C=O) in benzaldehyde?

• 3200–3600 cm−1
• 2100–2200 cm−1
• 1700–1740 cm−1
• 1500–1600 cm−1

Correct Answer: 1700–1740 cm−1

Q10. Benzaldehyde is primarily classified as which type of aromatic compound?

• Aromatic ketone
• Aromatic alcohol
• Aromatic aldehyde
• Aromatic acid

Correct Answer: Aromatic aldehyde

Q11. Which of the following statements about benzaldehyde’s solubility is correct?

• Highly soluble in water
• Insoluble in organic solvents
• Miscible with ethanol and diethyl ether but only slightly soluble in water
• Only soluble in supercritical CO2

Correct Answer: Miscible with ethanol and diethyl ether but only slightly soluble in water

Q12. Which method is commonly used industrially to prepare benzaldehyde from toluene?

• Nitration followed by reduction
• Chlorination to benzyl chloride then oxidation
• Direct formylation of toluene via Gattermann-Koch
• Hydrogenation of benzoic acid

Correct Answer: Chlorination to benzyl chloride then oxidation

Q13. What catalyst is commonly used in the benzoin condensation of benzaldehyde to give benzoin?

• Pd/C
• KCN (cyanide)
• AlCl3
• H2SO4

Correct Answer: KCN (cyanide)

Q14. Which electrophilic aromatic substitution orientation does the formyl group (-CHO) direct?

• Ortho/para directing and activating
• Meta directing and deactivating
• Ortho directing and deactivating
• Para directing and activating

Correct Answer: Meta directing and deactivating

Q15. Benzaldehyde gives a silver mirror with which reagent?

• Tollen’s reagent
• Benedict’s reagent
• Fehling’s solution
• Br2 in CCl4

Correct Answer: Tollen’s reagent

Q16. Which reaction transforms benzaldehyde into cinnamic acid derivatives when treated with an acid anhydride and base (Perkin reaction)?

• Perkin reaction
• Wittig reaction
• Aldol condensation
• Baeyer-Villiger oxidation

Correct Answer: Perkin reaction

Q17. Why can benzaldehyde not undergo a classical aldol condensation?

• Because it’s aromatic
• Because it lacks alpha hydrogen atoms
• Because it is too soluble in water
• Because it is a secondary carbonyl

Correct Answer: Because it lacks alpha hydrogen atoms

Q18. Which test reagent yields a magenta color with aldehydes, including benzaldehyde?

• 2,4-DNP (2,4-dinitrophenylhydrazine)
• Br2 in CCl4
• Schiff’s reagent
• KMnO4

Correct Answer: Schiff’s reagent

Q19. Which product forms when benzaldehyde reacts with primary amines?

• Acetal
• Schiff base (imine)
• Alcohol
• Enamine

Correct Answer: Schiff base (imine)

Q20. Which transformation converts benzaldehyde into benzyl alcohol?

• Oxidation with NaClO
• Reduction with NaBH4
• Tautomerization followed by hydrolysis
• Friedel-Crafts acylation

Correct Answer: Reduction with NaBH4

Q21. Benzaldehyde is used as a precursor in the synthesis of which common pharmaceutical intermediate?

• Paracetamol
• Benzylpenicillin
• Cinnamaldehyde derivatives and heterocyclic intermediates
• Insulin analogs

Correct Answer: Cinnamaldehyde derivatives and heterocyclic intermediates

Q22. Which side reaction must be controlled during oxidation of benzyl alcohol to benzaldehyde to prevent formation of benzoic acid?

• Over-oxidation
• Polymerization
• Hydrogenation
• Hydrolysis

Correct Answer: Over-oxidation

Q23. Which structural feature gives benzaldehyde its electrophilic character at the carbonyl carbon?

• Resonance donation from the benzene ring making C more negative
• Inductive and resonance withdrawal by the formyl group making carbonyl carbon electron-poor
• Presence of an adjacent hydroxyl group
• Conjugation with a nitro group

Correct Answer: Inductive and resonance withdrawal by the formyl group making carbonyl carbon electron-poor

Q24. Which reagent is commonly used to detect carbonyl compounds by forming hydrazones (orange/yellow precipitate)?

• 2,4-DNP (2,4-dinitrophenylhydrazine)
• Benedict’s reagent
• Tollen’s reagent
• Lucas reagent

Correct Answer: 2,4-DNP (2,4-dinitrophenylhydrazine)

Q25. In mass spectrometry, the molecular ion peak (M+) of benzaldehyde corresponds to m/z approximately equal to:

• 106
• 92
• 120
• 136

Correct Answer: 106

Q26. Benzaldehyde’s boiling point is approximately:

• 56 °C
• 98 °C
• 178 °C
• 250 °C

Correct Answer: 178 °C

Q27. Which reagent will give a positive test for benzaldehyde by forming a colored complex specifically with aldehydes and some ketones (not with carboxylic acids)?

• Br2 in CCl4
• Tollen’s reagent
• Schiff’s reagent
• KMnO4

Correct Answer: Schiff’s reagent

Q28. The carbonyl carbon of benzaldehyde typically appears around what ppm in 13C NMR?

• 20–40 ppm
• 60–80 ppm
• 120–140 ppm
• 190–200 ppm

Correct Answer: 190–200 ppm

Q29. Which of the following is NOT a common use of benzaldehyde?

• Flavoring and fragrance agent
• Intermediate in pharmaceuticals
• Active pharmaceutical ingredient for beta-blockers
• Precursor for benzylidene derivatives

Correct Answer: Active pharmaceutical ingredient for beta-blockers

Q30. Which metal catalyst would you avoid when attempting Friedel–Crafts alkylation on benzaldehyde due to deactivation by -CHO?

• AlCl3
• Pd/C
• PtO2
• Raney-Ni

Correct Answer: AlCl3

Q31. What happens when benzaldehyde is treated with bromine in acetic acid (electrophilic bromination conditions)?

• Easy bromination at the ring (high yield)
• Bromination is slow because -CHO is deactivating; mixture of products
• Immediate substitution of the formyl group
• Formation of benzyl bromide

Correct Answer: Bromination is slow because -CHO is deactivating; mixture of products

Q32. Which condition favors formation of benzoin from benzaldehyde (benzoin condensation)?

• Strong acid catalysis
• Base-free thermal conditions
• Cyanide ion catalysis
• Peroxide initiation

Correct Answer: Cyanide ion catalysis

Q33. Benzaldehyde can be converted to benzylidene derivatives via which type of reaction with active methylene compounds?

• Wittig reaction
• Aldol-type condensation (Knoevenagel condensation)
• Reduction with LiAlH4
• Baeyer-Villiger oxidation

Correct Answer: Aldol-type condensation (Knoevenagel condensation)

Q34. Which safety precaution is most relevant when handling benzaldehyde in a laboratory?

• It is non-toxic, no precautions needed
• Avoid inhalation and skin contact due to irritation and sensitization
• Must be handled under cryogenic conditions
• Requires handling under inert atmosphere because it spontaneously explodes

Correct Answer: Avoid inhalation and skin contact due to irritation and sensitization

Q35. Which transformation uses benzaldehyde and phenylacetic acid derivatives to form cinnamic acid analogs?

• Perkin reaction
• Michael addition
• Wolff–Kishner reduction
• Mannich reaction

Correct Answer: Perkin reaction

Q36. When benzaldehyde is treated with excess methanol in acid, what product is expected?

• Benzyl methyl ether
• Benzaldehyde dimethyl acetal (acetal formation)
• Methyl benzoate
• Benzyl alcohol

Correct Answer: Benzaldehyde dimethyl acetal (acetal formation)

Q37. Which analytical method would best quantify trace benzaldehyde in a pharmaceutical fragrance formulation?

• Thin layer chromatography (TLC)
• Gas chromatography (GC) with flame ionization detector
• Simple pH measurement
• Melting point determination

Correct Answer: Gas chromatography (GC) with flame ionization detector

Q38. In biosynthesis or metabolism, benzaldehyde is often oxidized to:

• Toluene
• Benzoic acid
• Benzyl alcohol
• Benzene

Correct Answer: Benzoic acid

Q39. Which reagent will convert benzaldehyde into an alkene via Wittig reaction?

• Ph3P=CH2 (a Wittig ylide)
• NaBH4
• KMnO4
• PCC

Correct Answer: Ph3P=CH2 (a Wittig ylide)

Q40. Which property of benzaldehyde must be considered when storing it in laboratory to prevent spoilage?

• It readily polymerizes to solid
• It oxidizes slowly to benzoic acid on exposure to air
• It sublimes at room temperature
• It decomposes explosively under light

Correct Answer: It oxidizes slowly to benzoic acid on exposure to air

Q41. Which derivative is formed by the reaction of benzaldehyde with 2,4-dinitrophenylhydrazine?

• Hydrazone (2,4-DNP derivative)
• Oxime
• Acetal
• Carboxylic acid

Correct Answer: Hydrazone (2,4-DNP derivative)

Q42. In medicinal chemistry, benzaldehyde is often used as a synthetic building block for:

• Peptide bond formation
• Construction of heterocycles and aromatic aldehyde-derived drugs
• Direct synthesis of steroid hormones
• Direct formation of polysaccharides

Correct Answer: Construction of heterocycles and aromatic aldehyde-derived drugs

Q43. Which reagent will reduce benzaldehyde directly to toluene under strong conditions?

• NaBH4
• H2 with Pt or Pd (catalytic hydrogenation) followed by decarbonylation
• K2Cr2O7
• Schiff’s reagent

Correct Answer: H2 with Pt or Pd (catalytic hydrogenation) followed by decarbonylation

Q44. Why is benzaldehyde often used as a model compound in studying aromatic aldehyde reactivity?

• Because it is non-reactive and inert
• Because it combines simple aromaticity with an aldehyde functional group and lacks alpha hydrogens, giving clear mechanistic outcomes
• Because it is a gas at room temperature and easy to handle
• Because it contains multiple stereocenters

Correct Answer: Because it combines simple aromaticity with an aldehyde functional group and lacks alpha hydrogens, giving clear mechanistic outcomes

Q45. Which statement about benzaldehyde’s acidity/basicity is correct?

• It is strongly basic due to the formyl group
• It is slightly acidic at the aldehydic hydrogen
• It is neither strongly acidic nor basic; it exhibits electrophilic carbonyl behavior
• It is a strong acid comparable to acetic acid

Correct Answer: It is neither strongly acidic nor basic; it exhibits electrophilic carbonyl behavior

Q46. Which of the following reagents is used to selectively oxidize benzyl alcohol to benzaldehyde without over-oxidation to benzoic acid?

• Chromic acid (H2CrO4)
• PCC (pyridinium chlorochromate)
• KMnO4 (hot)
• Strong nitric acid

Correct Answer: PCC (pyridinium chlorochromate)

Q47. Which heteroatom-containing nucleophile will readily add to the carbonyl carbon of benzaldehyde forming a reversible adduct in neutral conditions?

• Water (forming a hydrate)
• Chloride ion (forming alkyl chloride)
• Ether (forming acetal spontaneously)
• O2 gas

Correct Answer: Water (forming a hydrate)

Q48. Which derivative of benzaldehyde is commonly formed during protective acetal formation for aldehyde protection?

• Benzaldehyde oxide
• 1,1-dimethoxybenzene (acetal)
• Benzyl chloride
• Benzylidene chloride

Correct Answer: 1,1-dimethoxybenzene (acetal)

Q49. For spectrophotometric monitoring, which UV-Vis characteristic of benzaldehyde is useful due to conjugation with the aromatic ring?

• No UV absorption at all
• Strong n→π* transition around 270–300 nm
• Only visible light absorption >500 nm
• Only IR-active transitions

Correct Answer: Strong n→π* transition around 270–300 nm

Q50. Which environmental concern is associated with benzaldehyde handling and disposal?

• It bioaccumulates in fatty tissues and is persistent pollutant
• It is readily biodegradable and poses no hazard
• It can oxidize to benzoic acid and may require neutralization before disposal; avoid release to water systems
• It polymerizes to polyethylene in environment

Correct Answer: It can oxidize to benzoic acid and may require neutralization before disposal; avoid release to water systems

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com