Nomenclature of geometrical isomers – Cis/Trans MCQs With Answer
This concise guide helps B. Pharm students master the nomenclature of geometrical isomers—covering cis/trans and E/Z terminology, CIP priority rules, examples in alkenes and cycloalkanes, and pharmaceutical relevance. You will learn how stereochemistry alters drug polarity, receptor fit, stability, and pharmacokinetics, with clear rules for assigning cis, trans, E and Z configurations. Emphasis is placed on practical identification, naming conventions, and analytical techniques used in pharmaceutical chemistry to distinguish isomers. Strengthening these concepts is essential for medicinal chemistry, formulation, and quality control in pharmacy practice. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What defines geometrical (cis/trans) isomerism?
- Different connectivity of atoms in the molecule
- Same connectivity but different spatial arrangement due to restricted rotation
- Different molecular formulas
- Difference only in hydrogen positions on saturated carbon
Correct Answer: Same connectivity but different spatial arrangement due to restricted rotation
Q2. In alkene nomenclature, when are two substituents described as “cis”?
- When they are on adjacent carbon atoms
- When they are on the same side of the double bond
- When they have different priorities by CIP rules
- When they are on opposite sides of the double bond
Correct Answer: When they are on the same side of the double bond
Q3. What is the primary rule set used to assign E/Z configuration?
- Markovnikov’s rule
- Baeyer strain rule
- Cahn–Ingold–Prelog priority rules
- Hückel rule
Correct Answer: Cahn–Ingold–Prelog priority rules
Q4. Which 2-butene isomer has methyl groups on the same side?
- trans-2-butene
- cis-2-butene
- 1-butene
- iso-butene
Correct Answer: cis-2-butene
Q5. Which is generally more stable: cis-alkene or trans-alkene?
- Cis-alkene
- Trans-alkene
- They are equally stable
- Depends only on solvent polarity
Correct Answer: Trans-alkene
Q6. For E/Z assignment, what determines priority at a double-bonded carbon?
- Electronegativity of the molecule
- Atomic number of the atoms directly attached
- Molecular weight of substituents
- Bond order only
Correct Answer: Atomic number of the atoms directly attached
Q7. What does the “E” designation indicate in E/Z nomenclature?
- Higher-priority groups are on the same side
- Higher-priority groups are on opposite sides
- Both substituents are identical
- The molecule is chiral
Correct Answer: Higher-priority groups are on opposite sides
Q8. How is “cis” defined on a substituted cyclohexane ring?
- Substituents on adjacent carbons
- Substituents on the same face (both up or both down)
- Substituents with different CIP priorities
- Substituents in equatorial positions only
Correct Answer: Substituents on the same face (both up or both down)
Q9. Which 1,2-dimethylcyclohexane isomer is generally more stable?
- 1,2-cis (one axial, one equatorial)
- 1,2-trans (both equatorial)
- They have identical stability
- 1,2-trans (both axial)
Correct Answer: 1,2-trans (both equatorial)
Q10. Which analytical technique is commonly used to separate and analyze cis/trans isomers in pharmaceutical samples?
- Infrared spectroscopy alone
- Gas chromatography (GC)
- Elemental analysis
- Melting point determination
Correct Answer: Gas chromatography (GC)
Q11. Why is distinguishing cis/trans isomers important in drug development?
- Isomers always have identical potency
- Geometric isomers can differ in receptor binding, potency, and ADME
- It only matters for flavor of oral drugs
- It affects only the melting point
Correct Answer: Geometric isomers can differ in receptor binding, potency, and ADME
Q12. Which retinoid form is commonly more biologically active: cis-retinoic acid or all-trans-retinoic acid?
- cis-retinoic acid
- all-trans-retinoic acid
- Both are equally active
- Neither is biologically active
Correct Answer: all-trans-retinoic acid
Q13. According to CIP rules, which atom gives higher priority: oxygen or nitrogen when directly attached?
- Nitrogen
- Oxygen
- They are equal
- Carbon
Correct Answer: Oxygen
Q14. For the double bond CH3CH=CHCH2Cl, which substituents are compared for E/Z at the left carbon?
- H and CH3
- CH2Cl and H
- CH2 and Cl
- CH3 and Cl
Correct Answer: H and CH3
Q15. Which statement about meso compounds is correct?
- Meso compounds are always optically active
- Meso compounds have stereocenters but are achiral due to internal symmetry
- Meso means the compound has no stereocenters
- Meso compounds are identical to enantiomers
Correct Answer: Meso compounds have stereocenters but are achiral due to internal symmetry
Q16. In aromatic derivatives, cis/trans terminology is never used. True or false?
- True
- False
- Only true for monosubstituted aromatics
- True for heterocycles only
Correct Answer: False
Q17. Which of the following is a correct description: trans-1,2-dichloroethene has chlorine atoms where?
- On the same side of the double bond
- On opposite sides of the double bond
- Both on one carbon
- On adjacent carbons but same side only in cyclic forms
Correct Answer: On opposite sides of the double bond
Q18. When assigning priorities to substituents with identical atoms, what is the next criterion?
- Atomic mass of substituent group
- Compare next atoms along the chain until a difference is found
- Number of carbons in the substituent
- Physical state at room temperature
Correct Answer: Compare next atoms along the chain until a difference is found
Q19. Which is a pharmacologically relevant consequence of cis/trans isomerism?
- Only melting point changes
- Differences in solubility, permeability, and receptor selectivity
- They become different elements
- Isomers always interconvert instantly in vivo
Correct Answer: Differences in solubility, permeability, and receptor selectivity
Q20. In a double bond where the two highest priority groups are on the same side, the configuration is:
- E
- Z
- trans
- R
Correct Answer: Z
Q21. For the alkene CHCl=CHBr, which atom has the highest priority at the left carbon?
- Hydrogen
- Chlorine
- Bromine
- Carbon
Correct Answer: Chlorine
Q22. Which property often differs most markedly between cis and trans isomers?
- Boiling point
- Chemical formula
- Atomic number
- Color of the element
Correct Answer: Boiling point
Q23. Which is a correct statement about E/Z vs cis/trans?
- cis/trans is always preferred over E/Z for complex substituents
- E/Z is unambiguous for any substituent; cis/trans can be ambiguous for dissimilar groups
- They are interchangeable terms in all cases
- cis/trans uses CIP priorities
Correct Answer: E/Z is unambiguous for any substituent; cis/trans can be ambiguous for dissimilar groups
Q24. Which isomer of stilbene is generally more photoreactive: cis-stilbene or trans-stilbene?
- trans-stilbene
- cis-stilbene
- Neither
- Both equally photostable
Correct Answer: cis-stilbene
Q25. Which factor can lock a molecule into a cis or trans form preventing rotation?
- Single bond between carbons
- Double bond or ring structure causing restricted rotation
- Low molecular weight only
- Presence of only hydrogen substituents
Correct Answer: Double bond or ring structure causing restricted rotation
Q26. In naming an alkene with multiple substituents, E/Z designation refers to:
- The absolute configuration at stereocenters
- The relative positions of the two highest priority substituents across the double bond
- The order of substituents alphabetically
- Speed of rotation around the bond
Correct Answer: The relative positions of the two highest priority substituents across the double bond
Q27. Which pharmaceutical example shows activity difference between geometric isomers?
- Thalidomide enantiomers only
- Retinoids where all-trans and cis differ in activity
- Metals like sodium and potassium
- Simple alkanes that lack stereochemistry
Correct Answer: Retinoids where all-trans and cis differ in activity
Q28. For the molecule 1,1-dichloroethene (CH2=CCl2), is cis/trans nomenclature applicable?
- Yes, cis and trans both exist
- No, because the two substituents on one carbon are identical
- Only in solution
- Yes, but only at high temperature
Correct Answer: No, because the two substituents on one carbon are identical
Q29. When two identical substituents are attached to the same carbon of a double bond, the molecule is:
- Capable of cis/trans isomerism
- Unable to show cis/trans isomerism about that double bond
- Always chiral
- Always meso
Correct Answer: Unable to show cis/trans isomerism about that double bond
Q30. Which of these best describes a trans cyclohexane disubstituted at 1,4 positions in the chair form?
- Both substituents are on the same face
- Substituents are on opposite faces (one up, one down)
- They must both be axial
- They must both be equatorial only
Correct Answer: Substituents are on opposite faces (one up, one down)
Q31. Which outcome is expected when a cis isomer converts to trans under catalytic hydrogenation?
- They always interconvert to form racemates
- Double bond is saturated; geometry is lost as single bond forms
- Trans isomer concentration increases without hydrogenation
- No chemical change occurs
Correct Answer: Double bond is saturated; geometry is lost as single bond forms
Q32. In drug analysis, which spectroscopic change might indicate cis/trans isomerism?
- Identical IR spectra always
- Different NMR coupling constants and chemical shifts
- Change only in elemental composition
- No change in chromatography behavior
Correct Answer: Different NMR coupling constants and chemical shifts
Q33. For the alkene with substituents: left carbon H and Br, right carbon H and Cl, which pair determines E/Z?
- H vs Br on left and H vs Cl on right using priorities
- Only the halogens compared regardless of position
- Molecular weight comparison only
- Only hydrogen positions matter
Correct Answer: H vs Br on left and H vs Cl on right using priorities
Q34. What is the effect of steric hindrance on cis-alkenes?
- Cis-alkenes are always less sterically hindered
- Cis-alkenes often experience increased steric strain and higher energy
- Steric hindrance is irrelevant to stability
- Cis-alkenes have less polarity
Correct Answer: Cis-alkenes often experience increased steric strain and higher energy
Q35. Which example would require E/Z nomenclature rather than cis/trans?
- 2-butene with identical substituents on each carbon
- Alkene where substituents on one carbon are H and CH3 and on the other are Cl and Br
- Simple cycloalkane with two identical substituents
- Molecule with no double bond
Correct Answer: Alkene where substituents on one carbon are H and CH3 and on the other are Cl and Br
Q36. Which property often increases in cis isomers compared to trans isomers?
- Melting point generally
- Polarity and dipole moment
- Symmetry always increases
- Boiling point always decreases
Correct Answer: Polarity and dipole moment
Q37. How are double bonds prioritized if directly attached atoms are identical (e.g., both carbons attached to carbons)?
- Ignore further atoms and call them equal
- Compare atoms one bond further out along each substituent
- Use molecular weight only
- Choose randomly
Correct Answer: Compare atoms one bond further out along each substituent
Q38. Which geometric isomer generally has a higher melting point due to better crystal packing?
- cis isomer
- trans isomer
- They always have equal melting points
- Isomerism does not affect melting point
Correct Answer: trans isomer
Q39. Which of the following statements about geometric isomers and metabolism is true?
- Metabolic enzymes cannot distinguish geometric isomers
- Geometric isomers can be metabolized differently affecting half-life
- Geometric isomers always interconvert in the bloodstream
- Metabolism only depends on molecular weight
Correct Answer: Geometric isomers can be metabolized differently affecting half-life
Q40. When two identical substituents are on opposite faces of a cyclohexane, they are termed:
- cis
- trans
- enantioisomers
- diastereomers
Correct Answer: trans
Q41. Which factor makes cis/trans assignment crucial for a chiral drug candidate?
- Geometric isomerism never affects chirality
- Different geometry can alter 3D shape and chiral recognition by receptors
- Cis/trans only affects taste, not activity
- It only influences color and aroma
Correct Answer: Different geometry can alter 3D shape and chiral recognition by receptors
Q42. Which statement is correct about E/Z naming and stereocenters?
- E/Z applies to double bonds and is independent of adjacent stereocenters
- E/Z is used for stereocenters like R/S
- E/Z is only used when R/S fails
- E/Z and R/S are identical systems
Correct Answer: E/Z applies to double bonds and is independent of adjacent stereocenters
Q43. For the alkene with substituents ranked by CIP, if highest priorities are opposite, the config is:
- Z
- E
- Cis only
- R
Correct Answer: E
Q44. In naming, when cis/trans and E/Z both apply, which is preferred by IUPAC for dissimilar substituents?
- cis/trans since it is traditional
- E/Z as it is unambiguous
- Neither; use R/S
- Use alphabetical order only
Correct Answer: E/Z as it is unambiguous
Q45. Which experimental observation suggests the presence of geometric isomers in a sample?
- Single, sharp NMR signal for all protons
- Multiple sets of NMR signals and multiple peaks in GC
- Identical TLC retention for all components
- No change in UV-visible absorption
Correct Answer: Multiple sets of NMR signals and multiple peaks in GC
Q46. Which molecule can show cis/trans isomerism: 1-butene, 2-butene, or 3-butene?
- 1-butene only
- 2-butene only
- 3-butene only
- 1- and 3-butene but not 2-butene
Correct Answer: 2-butene only
Q47. What effect does conjugation have on geometric isomer stability?
- Conjugation typically destabilizes both isomers equally
- Conjugation can stabilize an isomer by delocalizing electrons, affecting relative energies
- Conjugation always favors cis isomer
- Conjugation is irrelevant to alkene stability
Correct Answer: Conjugation can stabilize an isomer by delocalizing electrons, affecting relative energies
Q48. For the alkene PhCH=CH2 (styrene), can cis/trans nomenclature be applied meaningfully?
- Yes, because both substituents on the vinyl carbon are different
- No, because one carbon has two hydrogens and substituents are identical on that carbon
- Yes, because aromatic rings allow cis/trans distinctions always
- No, because styrene is chiral
Correct Answer: No, because one carbon has two hydrogens and substituents are identical on that carbon
Q49. In pharmaceutical formulation, why might a trans isomer be favored over a cis isomer?
- Trans isomers are always less soluble and thus preferred
- Trans isomers sometimes offer better stability, lower reactivity, or improved bioavailability
- Cis isomers never bind to receptors
- Regulatory agencies mandate trans forms only
Correct Answer: Trans isomers sometimes offer better stability, lower reactivity, or improved bioavailability
Q50. Which practice is essential when reporting geometric isomerism in a drug candidate?
- Report only melting point
- Clearly assign and report E/Z or cis/trans using CIP rules and provide analytical evidence
- State only the molecular formula
- Avoid stereochemical descriptors to prevent confusion
Correct Answer: Clearly assign and report E/Z or cis/trans using CIP rules and provide analytical evidence
