Pharmacy Pharmaceutical Chemistry 3 — Questions and Answers
Question 1: Which chemical reaction is used in the synthesis of esters from carboxylic acids?
- Fischer esterification (Correct answer)
- Aldol condensation
- Diels-Alder reaction
- Grignard reaction
Correct answer: Fischer esterification
Fischer esterification involves the acid-catalyzed condensation of a carboxylic acid with an alcohol to form an ester and water.
Question 2: The term 'bioisostere' in medicinal chemistry refers to:
- Two drugs with identical chemical structures
- A substituent or group that produces similar biological effects to another group (Correct answer)
- A drug and its metabolite
- Two drugs with identical molecular weights
Correct answer: A substituent or group that produces similar biological effects to another group
Bioisosteres are atoms or groups that produce broadly similar biological activity due to similar size, electronegativity, or electronic effects.
Question 3: Which oxidation state characterizes a sulfonic acid group (-SO3H)?
- +2
- +4
- +6 (Correct answer)
- +8
Correct answer: +6
In a sulfonic acid (-SO3H), sulfur has an oxidation state of +6, the same as in sulfuric acid H2SO4.
Question 4: In pharmacokinetics, the concept of 'ionization trapping' in the stomach means that:
- Acidic drugs remain unionized and are readily absorbed from the stomach
- Basic drugs become highly ionized at low gastric pH and are poorly absorbed
- Basic drugs are trapped in the stomach because ionization reduces membrane permeability (Correct answer)
- Acidic drugs are converted to their salt forms and cannot be absorbed
Correct answer: Basic drugs are trapped in the stomach because ionization reduces membrane permeability
Basic drugs become protonated (ionized) in the acidic stomach environment, making them water-soluble but membrane-impermeable, trapping them in the gastric lumen.
Question 5: Which reaction converts a primary amine to a diazonium salt?
- Acylation
- Diazotization (with NaNO2/HCl) (Correct answer)
- Reductive amination
- Hofmann elimination
Correct answer: Diazotization (with NaNO2/HCl)
Diazotization reacts a primary aromatic amine with sodium nitrite (NaNO2) in acidic (HCl) conditions at 0–5°C to form a diazonium salt (ArN2+Cl-).
Question 6: Hydrolysis of an amide bond under acidic conditions produces:
- An ester and an amine
- A carboxylic acid and an amine (or ammonium salt) (Correct answer)
- An alcohol and a nitrile
- A ketone and water
Correct answer: A carboxylic acid and an amine (or ammonium salt)
Acid hydrolysis of an amide cleaves the C-N bond, yielding a carboxylic acid and the protonated amine (ammonium salt).
Question 7: Which analytical technique is most commonly used to confirm the identity and purity of a crystalline drug substance by its unique molecular fingerprint?
- UV-Vis spectroscopy
- Infrared (IR) spectroscopy (Correct answer)
- Atomic absorption spectroscopy
- Flame photometry
Correct answer: Infrared (IR) spectroscopy
IR spectroscopy identifies functional groups and provides a molecular fingerprint region (1500–400 cm⁻¹) unique to each compound, used for identity confirmation.
Pharmacy Pharmaceutical Chemistry 3
Which chemical reaction is used in the synthesis of esters from carboxylic acids?