Structure and uses of paraldehyde MCQs With Answer

Paraldehyde is a cyclic trimer of acetaldehyde with the IUPAC name 2,4,6-trimethyl-1,3,5-trioxane. This concise review on structure and uses of paraldehyde MCQs with answer is tailored for B.Pharm students and highlights chemical structure, synthesis, physicochemical properties, pharmacology and clinical applications. Emphasis is placed on acid-catalyzed trimerization, ring stability, metabolism to acetaldehyde, CNS-depressant and anticonvulsant effects, administration routes and common incompatibilities. Questions also cover formulation, stability, analytical assays (GC/IR), adverse effects, drug interactions and regulatory considerations to deepen practical understanding. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which of the following best describes the chemical structure of paraldehyde?

• Acyclic dimer of acetaldehyde
• Cyclic trimer of acetaldehyde
• Polymeric resin of acetaldehyde
• Monomeric aldehyde derivative

Correct Answer: Cyclic trimer of acetaldehyde

Q2. What is the IUPAC name of paraldehyde?

• 1,3,5-trioxane
• 2,4,6-trimethyl-1,3,5-trioxane
• Acetaldehyde polymer
• Ethylidene glycol

Correct Answer: 2,4,6-trimethyl-1,3,5-trioxane

Q3. Paraldehyde is formed industrially by which type of reaction of acetaldehyde?

• Oxidation
• Reduction
• Acid-catalyzed trimerization
• Nucleophilic substitution

Correct Answer: Acid-catalyzed trimerization

Q4. Which functional group is characteristic of paraldehyde’s cyclic structure?

• Acetal (trioxane) ring
• Ketone group
• Carboxylic acid
• Ether linkage only

Correct Answer: Acetal (trioxane) ring

Q5. Which statement about paraldehyde’s solubility is most accurate?

• Completely miscible with water
• Sparingly soluble in water but miscible with ethanol
• Insoluble in organic solvents
• Soluble only in strong acids

Correct Answer: Sparingly soluble in water but miscible with ethanol

Q6. The conversion of paraldehyde back to acetaldehyde is promoted by:

• Base-catalyzed hydrolysis
• Acid-catalyzed hydrolysis
• Photolysis only
• Neutral aqueous conditions

Correct Answer: Acid-catalyzed hydrolysis

Q7. Which pharmacological action is classically associated with paraldehyde?

• Stimulant
• CNS depressant and anticonvulsant
• Antibiotic
• Anti-inflammatory

Correct Answer: CNS depressant and anticonvulsant

Q8. Paraldehyde has historically been used in medicine primarily as a:

• Topical antiseptic
• Oral hypoglycemic
• Sedative-hypnotic and anticonvulsant
• Local anaesthetic

Correct Answer: Sedative-hypnotic and anticonvulsant

Q9. The molecular formula of paraldehyde is:

• C3H6O
• C6H12O3
• C4H8O2
• C2H4O

Correct Answer: C6H12O3

Q10. Which analytical technique is most appropriate for qualitative identification of paraldehyde in a formulation?

• Gas chromatography (GC)
• Atomic absorption spectroscopy
• Thermogravimetric analysis only
• Flame photometry

Correct Answer: Gas chromatography (GC)

Q11. Paraldehyde administration is sometimes given rectally in seizures because:

• It is inactive orally
• Oral route causes local gastric irritation and vomiting
• Rectal route increases first-pass metabolism
• It cannot cross the gut wall

Correct Answer: Oral route causes local gastric irritation and vomiting

Q12. Metabolism of paraldehyde in the body principally yields which intermediate?

• Acetone
• Acetaldehyde
• Formaldehyde
• Benzoic acid

Correct Answer: Acetaldehyde

Q13. Which property explains paraldehyde’s characteristic pungent odor and irritant effects?

• Presence of free aldehyde functional group in equilibrium
• High molecular weight polymeric structure
• Lack of volatility
• Presence of nitrogen moieties

Correct Answer: Presence of free aldehyde functional group in equilibrium

Q14. Incompatibility of paraldehyde with which class of compounds is clinically relevant?

• CNS depressants (additive effects)
• Topical corticosteroids
• Antacids only
• Insulin

Correct Answer: CNS depressants (additive effects)

Q15. The ring in paraldehyde is best described as a:

• Five-membered lactone
• Six-membered trioxane ring
• Four-membered oxetane
• Seven-membered ether ring

Correct Answer: Six-membered trioxane ring

Q16. Which statement about paraldehyde’s stability is true?

• Stable under strong acid conditions
• Stable under basic conditions but hydrolyses under strong acid
• Unstable in basic solutions only
• Stable to both strong acid and base

Correct Answer: Stable under basic conditions but hydrolyses under strong acid

Q17. The antiseizure effect of paraldehyde is primarily due to:

• Specific sodium channel blockade
• Non-specific CNS depression and enhancement of inhibitory tone
• Inhibition of acetylcholinesterase
• Activation of opioid receptors

Correct Answer: Non-specific CNS depression and enhancement of inhibitory tone

Q18. Which of the following routes avoids first-pass gastric irritation with paraldehyde?

• Oral diluted in water
• Rectal administration
• Subcutaneous injection
• Topical application

Correct Answer: Rectal administration

Q19. For pharmaceutical analysis, infrared (IR) spectroscopy of paraldehyde would most characteristically show bands related to:

• Nitrile stretch
• Acetal (C–O) stretching vibrations
• Carboxylate anion bands
• Aromatic C–H stretching only

Correct Answer: Acetal (C–O) stretching vibrations

Q20. In formulation practice, paraldehyde is commonly handled with caution because it is:

• Non-flammable and inert
• Volatile, pungent and a respiratory irritant
• Highly basic
• Non-reactive with oxidizers

Correct Answer: Volatile, pungent and a respiratory irritant

Q21. Which of the following is a correct statement about paraldehyde’s legal/clinical status?

• It is a first-line modern antiepileptic for chronic therapy
• Its clinical use has declined due to side effects and alternatives
• It is approved for topical wound healing
• It is routinely used as an oral hypoglycemic

Correct Answer: Its clinical use has declined due to side effects and alternatives

Q22. Paraldehyde reacts back to acetaldehyde under acidic conditions; this is an example of:

• Polymerization
• Depolymerization (back-reaction/hydrolysis)
• Oxidative cleavage
• Radical substitution

Correct Answer: Depolymerization (back-reaction/hydrolysis)

Q23. Which pharmaceutical precaution is important when dispensing paraldehyde?

• Advise patients of sweet odor
• Warn about strong, unpleasant odor and potential nausea
• Recommend high-temperature storage
• Encourage mixing with acidic beverages

Correct Answer: Warn about strong, unpleasant odor and potential nausea

Q24. Which metabolic pathway handles acetaldehyde produced from paraldehyde?

• Oxidation by aldehyde dehydrogenase to acetate
• Reduction to ethanol exclusively
• Conjugation to glutathione only
• Methylation to methanol

Correct Answer: Oxidation by aldehyde dehydrogenase to acetate

Q25. Which adverse effect is most commonly associated with paraldehyde administration?

• Severe hypertension
• Respiratory depression and vomiting
• Hyperactivity and tremors
• Renal failure

Correct Answer: Respiratory depression and vomiting

Q26. In organic chemistry terms, paraldehyde is classified as a:

• Polyacetal (trioxane) derivative
• Simple ketone
• Carboxylic acid derivative
• Aldol condensation product

Correct Answer: Polyacetal (trioxane) derivative

Q27. Which statement about paraldehyde’s odor and patient acceptance is correct?

• It has no detectable odor
• Its pungent odor often limits oral use
• It has a sweet, pleasant aroma
• It is odorless when mixed with ethanol

Correct Answer: Its pungent odor often limits oral use

Q28. Which technique is preferred to quantify paraldehyde in a formulation for quality control?

• UV-Vis spectrophotometry without derivatization
• Gas chromatography with appropriate detector
• Colorimetric assay for proteins
• Titration with sodium hydroxide

Correct Answer: Gas chromatography with appropriate detector

Q29. Paraldehyde’s primary mechanism in seizure control is best described as:

• Enhancement of inhibitory neurotransmission and global CNS depression
• Selective inhibition of NMDA receptors only
• Activation of adrenergic receptors
• Direct blockade of calcium channels only

Correct Answer: Enhancement of inhibitory neurotransmission and global CNS depression

Q30. Which of the following is a correct statement about paraldehyde storage?

• Store in well-sealed containers away from acids
• Store exposed to air and light for stability
• Must be stored frozen at -80°C
• Store with strong oxidizing agents

Correct Answer: Store in well-sealed containers away from acids

Q31. Which chemical reagent can catalyze the formation of paraldehyde from acetaldehyde?

• Strong base like NaOH
• Acid catalyst like HCl
• Neutral salt solution
• Peroxide initiator only

Correct Answer: Acid catalyst like HCl

Q32. Why is paraldehyde rarely used as a first-line anticonvulsant today?

• Because it has no clinical efficacy
• Due to side effects, odor, and safer alternatives
• Because it is extremely expensive
• Because it causes permanent immunity

Correct Answer: Due to side effects, odor, and safer alternatives

Q33. Paraldehyde can be described as which of the following in terms of volatility and handling?

• Highly volatile and requires ventilation precautions
• Non-volatile and safe to handle without precautions
• Solid at room temperature and inert
• Completely immiscible with organic solvents

Correct Answer: Highly volatile and requires ventilation precautions

Q34. Which of these is a likely drug interaction concern with paraldehyde?

• Antagonism with benzodiazepines
• Additive CNS depression with opioids and alcohol
• Prevention of antacid action
• Enhancement of antibiotic potency

Correct Answer: Additive CNS depression with opioids and alcohol

Q35. In the laboratory, depolymerization of paraldehyde to produce acetaldehyde requires:

• Strong basic conditions only
• Acidic hydrolysis or heating
• UV irradiation only
• Oxidative reagents exclusively

Correct Answer: Acidic hydrolysis or heating

Q36. Which formulation consideration is important when preparing paraldehyde for administration?

• Mixing with strong acids to neutralize odor
• Dilution with suitable solvents to reduce irritation and vomiting
• Heating the product to increase potency
• Adding oxidizers to stabilize it

Correct Answer: Dilution with suitable solvents to reduce irritation and vomiting

Q37. A structural feature that distinguishes paraldehyde from acetaldehyde is:

• Presence of three methyl groups attached to a trioxane ring
• Lack of carbonyl functionality entirely
• Presence of an aromatic ring
• Long aliphatic chain

Correct Answer: Presence of three methyl groups attached to a trioxane ring

Q38. Occupational exposure controls for paraldehyde should include:

• Open-air handling without PPE
• Local exhaust ventilation and respiratory protection as needed
• Storage with strong acids for safety
• Exposure to sunlight to neutralize odor

Correct Answer: Local exhaust ventilation and respiratory protection as needed

Q39. Which statement about paraldehyde’s use in alcohol withdrawal is true?

• It is the current first-line recommended therapy
• It was historically used for its sedative properties in withdrawal
• It has stimulant effects that worsen withdrawal
• It directly blocks alcohol receptors

Correct Answer: It was historically used for its sedative properties in withdrawal

Q40. Which laboratory safety data point is most relevant when prescribing or storing paraldehyde?

• Explosive limit in water
• Flammability and compatibility with oxidizers
• Its radioactivity
• Ability to polymerize on cooling

Correct Answer: Flammability and compatibility with oxidizers

Q41. In a question bank about paraldehyde, a concept-testing MCQ on ring nomenclature would likely ask about:

• Number of carbonyl groups present
• Identification as a 1,3,5-trioxane derivative
• Presence of tertiary amine functionality
• Number of aromatic rings

Correct Answer: Identification as a 1,3,5-trioxane derivative

Q42. Which is a correct practical tip for administering paraldehyde orally if necessary?

• Give undiluted to maximize absorption
• Dilute in an appropriate solvent and administer cautiously due to vomiting risk
• Mix with strong acids to prevent hydrolysis
• Only administer after heating

Correct Answer: Dilute in an appropriate solvent and administer cautiously due to vomiting risk

Q43. Which of the following best describes paraldehyde’s historical role in anaesthesia?

• Inhalational anaesthetic agent
• Pre-anesthetic sedative-hypnotic aid
• Muscle relaxant used during surgery
• Primary analgesic agent

Correct Answer: Pre-anesthetic sedative-hypnotic aid

Q44. When considering formulation stability, paraldehyde is most likely to degrade in the presence of:

• Neutral salts
• Strong acids and moisture
• Nonpolar organic solvents
• Inert gases

Correct Answer: Strong acids and moisture

Q45. Which exam-focused concept about paraldehyde would be important for B.Pharm students to memorize?

• IUPAC name and trimeric origin from acetaldehyde
• Molecular weight of benzene
• Mechanism of action of penicillin
• Vitamin C biosynthesis pathway

Correct Answer: IUPAC name and trimeric origin from acetaldehyde

Q46. Paraldehyde’s CNS depressant effects make it potentially dangerous when combined with:

• Caffeine
• Benzodiazepines and opioids
• Vitamin supplements
• Topical creams

Correct Answer: Benzodiazepines and opioids

Q47. Which compound is the monomeric precursor of paraldehyde?

• Formaldehyde
• Acetaldehyde
• Acetone
• Propanal

Correct Answer: Acetaldehyde

Q48. For quality control of paraldehyde batches, which impurity would be of particular concern?

• Residual acetaldehyde due to depolymerization
• Residual benzene only
• Excess water-insoluble solids
• High levels of sodium chloride

Correct Answer: Residual acetaldehyde due to depolymerization

Q49. Paraldehyde’s conversion to acetaldehyde in vivo may contribute to which clinical symptom?

• Increased appetite
• Nausea and vomiting due to local irritation and aldehyde effects
• Improved mood exclusively
• Enhanced renal clearance

Correct Answer: Nausea and vomiting due to local irritation and aldehyde effects

Q50. Which educational focus is most valuable for B.Pharm students studying paraldehyde?

• Memorizing unrelated drug trade names
• Understanding chemical structure, synthesis, pharmacology, formulation and safety
• Learning only about topical uses
• Focusing exclusively on cost analysis

Correct Answer: Understanding chemical structure, synthesis, pharmacology, formulation and safety

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