Isomerism Structural and Stereoisomerism - UNSOLVED PRACTICE SET

Q7. Define isomerism. Differentiate between structural isomerism and stereoisomerism with one example of each.

Q8. What is meant by a chiral carbon atom (stereocentre)? Draw the structure of 2-butanol and identify if it has a chiral centre.

Q9. Differentiate between cis and trans isomers with a suitable example. Why can't terminal alkenes (like propene) show geometrical isomerism?

Q10. Explain the difference between enantiomers and diastereomers. Do enantiomers have identical physical properties?

Q11. Your teacher shows you a model of lactic acid (CH₃–CH(OH)–COOH) and asks why it rotates plane-polarised light. Explain the concept of optical activity using this example.

Q12. What are conformers? Draw the Newman projections of ethane showing eclipsed and staggered conformations.

Q13. Discuss the different types of structural isomerism with examples:

(a) Chain isomerism

(b) Position isomerism

(c) Functional group isomerism

(d) Metamerism

For each type, give the definition, the condition required, and one example with structures.

Q14. Explain stereoisomerism in detail:

(a) Geometrical isomerism — cis-trans isomerism in alkenes, conditions for its occurrence

(b) Optical isomerism — chirality, enantiomers, racemic mixture, d and l notation

(c) Draw the cis and trans isomers of 2-butene

(d) Draw the enantiomers of lactic acid and explain why they are non-superimposable mirror images

Q15. Isomerism has profound implications in biology and medicine. Discuss:

(a) Why the human body can distinguish between optical isomers (e.g., D-glucose vs. L-glucose)

(b) The thalidomide tragedy and why one enantiomer was therapeutic while the other caused birth defects

(c) Why Indian pharmaceutical companies invest heavily in chiral separation technologies

(d) The concept of "handedness" in molecules and its similarity to your left and right hands

Q16. A compound has the molecular formula C₅H₁₂.

(a) Draw all possible structural isomers and name them according to IUPAC nomenclature.

(b) Identify which isomer has the highest boiling point and explain why.

(c) How many of these isomers have a chiral centre? Justify your answer.

Q17. Consider the compound 2,3-dichlorobutane (CH₃–CH(Cl)–CH(Cl)–CH₃).

(a) Draw all possible stereoisomers of this compound.

(b) Identify which pairs are enantiomers and which are diastereomers.

(c) Does this compound have a meso form? If yes, draw its structure and explain why it is optically inactive despite having chiral centres.

Q18. A pharmaceutical company in Mumbai is developing a chiral drug with the formula C₉H₁₁NO₂.

(a) Calculate the degree of unsaturation for this compound.

(b) If the drug has one chiral centre and the desired therapeutic effect comes only from the (R)-enantiomer, calculate the percentage of "waste" product if a racemic mixture is produced.

(c) Suggest one method to separate the desired enantiomer from the racemic mixture.