Limitations of Baeyer’s strain theory MCQs With Answer

Limitations of Baeyer’s strain theory MCQs With Answer

Baeyer’s strain theory historically explained ring strain by assuming cyclic compounds are planar and that deviation from the tetrahedral angle (109.5°) creates angle strain. For B. Pharm students preparing for organic chemistry and medicinal chemistry exams, understanding the theory’s limitations is essential: it overlooks torsional (eclipsing) strain, conformational flexibility (e.g., chair/boat forms), hyperconjugation, bent bonds in small rings, and transannular interactions in medium rings. These exceptions affect ring stability, reactivity, and heat of combustion data used in drug design. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which statement best describes the fundamental assumption of Baeyer’s strain theory?

• Cyclic rings are flexible and relieve strain by torsional motion
• Cyclic rings prefer nonplanar conformations to minimize torsional strain
• Cyclic rings are planar and angle strain arises from deviation from tetrahedral 109.5°
• Cycloalkanes have zero strain regardless of ring size

Correct Answer: Cyclic rings are planar and angle strain arises from deviation from tetrahedral 109.5°

Q2. Which experimental observation directly contradicted Baeyer’s prediction about cyclohexane?

• High heat of combustion consistent with a planar structure
• Existence of a low-energy chair conformation with negligible angle strain
• Planar cyclohexane being more stable than chair form
• Absence of any conformational isomers

Correct Answer: Existence of a low-energy chair conformation with negligible angle strain

Q3. Which type of strain did Baeyer’s original theory largely ignore?

• Angle strain
• Torsional (eclipsing) strain
• Ring strain due to deviation from 109.5°
• Heat of combustion

Correct Answer: Torsional (eclipsing) strain

Q4. Why is cyclopropane more strained than Baeyer predicted based only on angle strain?

• Because cyclopropane is planar and has no torsional strain
• Due to bent (banana) bonds and increased s-character affecting bonding
• Because cyclopropane adopts a chair conformation
• Because it has transannular interactions

Correct Answer: Due to bent (banana) bonds and increased s-character affecting bonding

Q5. Baeyer’s theory would predict very high strain for cyclohexane. Why is this prediction incorrect?

• Cyclohexane actually has a planar structure with high torsional strain
• Cyclohexane adopts a chair conformation that relieves angle and torsional strain
• Cyclohexane has delocalized π-electrons that stabilize the ring
• Cyclohexane is aromatic and thus unusually stable

Correct Answer: Cyclohexane adopts a chair conformation that relieves angle and torsional strain

Q6. Which measurement method provided direct evidence that Baeyer’s angle-only approach was incomplete?

• Infrared spectroscopy alone
• Heat of combustion measurements (thermochemical data)
• Simple molecular weight determination
• Thin-layer chromatography

Correct Answer: Heat of combustion measurements (thermochemical data)

Q7. What is a key limitation of using only heat of combustion to infer ring strain in cycloalkanes?

• Heat of combustion cannot detect angle strain at all
• It conflates angle strain, torsional strain, and changes in hybridization
• It is unaffected by conformational changes
• It only applies to aromatic systems

Correct Answer: It conflates angle strain, torsional strain, and changes in hybridization

Q8. Which ring size most directly revealed the need to consider torsional strain and nonplanarity beyond Baeyer’s model?

• Cyclohexane
• Cycloheptane
• Cyclopropane
• Cyclodecane

Correct Answer: Cyclohexane

Q9. Baeyer’s theory cannot account for which of the following conformational phenomena?

• Planar triangular geometry of cyclopropane
• Chair–boat interconversion and equatorial preference in cyclohexane
• Length of C–C single bonds in alkanes
• Basicity trends in amines

Correct Answer: Chair–boat interconversion and equatorial preference in cyclohexane

Q10. Which concept explains why cyclobutane is puckered rather than planar, contrary to Baeyer’s planar assumption?

• Torsional strain relief by adopting a nonplanar conformation
• Increased aromatic stabilization
• Formation of double bonds in the ring
• Transannular hydrogen bonding

Correct Answer: Torsional strain relief by adopting a nonplanar conformation

Q11. How does hyperconjugation undermine a pure angle-strain explanation for ring stability?

• Hyperconjugation increases only angle strain
• Hyperconjugation contributes electronic stabilization not included in angle-only models
• Hyperconjugation causes rings to break easily
• Hyperconjugation converts single bonds to double bonds

Correct Answer: Hyperconjugation contributes electronic stabilization not included in angle-only models

Q12. Baeyer’s theory would predict which trend for ring strain vs ring size, and how does experiment differ?

• Predicts monotonic decrease with size; experiment shows minimum at six-member ring
• Predicts oscillation; experiment shows linear increase
• Predicts six-member rings most strained; experiment shows cyclohexane least strained
• Predicts no strain at any size; experiment shows maximum strain at eight-member rings

Correct Answer: Predicts six-member rings most strained; experiment shows cyclohexane least strained

Q13. Why are medium-sized rings (8–11 members) often more strained than Baeyer’s theory anticipates?

• They are fully planar and suffer only angle strain
• They experience transannular (through-space) interactions and conformational restrictions
• They form aromatic systems that increase apparent strain
• They have no torsional strain due to free rotation

Correct Answer: They experience transannular (through-space) interactions and conformational restrictions

Q14. Which modern concept complements Baeyer’s theory to explain observed ring stabilities?

• Only valence shell electron pair repulsion (VSEPR)
• Conformational analysis including torsional strain, steric effects, and hyperconjugation
• Simple molecular orbital theory only for double bonds
• Elimination of all covalent bonding concepts

Correct Answer: Conformational analysis including torsional strain, steric effects, and hyperconjugation

Q15. Baeyer’s model does not properly predict stability of bridged bicyclic systems because it ignores:

• Angle strain entirely
• Conformational constraints and bridgehead interactions that affect hybridization
• Mass of atoms in the ring
• Presence of heteroatoms only

Correct Answer: Conformational constraints and bridgehead interactions that affect hybridization

Q16. Which of the following best describes “bent bonds” in cyclopropane and why Baeyer’s theory misses it?

• Typical σ-bonds with ideal 109.5° geometry; Baeyer includes this
• σ-bonds that are bent (banana bonds) to allow ~60° ring with unusual orbital overlap, not considered by angle-only models
• π-bonds formed in cyclopropane giving aromaticity
• Hydrogen bonds stabilizing the ring

Correct Answer: σ-bonds that are bent (banana bonds) to allow ~60° ring with unusual orbital overlap, not considered by angle-only models

Q17. Which concept explains why substitution at cyclohexane axial positions is less stable than equatorial positions — a point Baeyer’s theory cannot predict?

• Angle strain differences only
• 1,3-diaxial steric interactions and torsional strain affecting substituent orientation
• Basicity differences of substituents
• Electronegativity of hydrogen atoms

Correct Answer: 1,3-diaxial steric interactions and torsional strain affecting substituent orientation

Q18. Which best explains why cyclopentane is not planar although Baeyer’s model might assume so?

• It adopts an envelope conformation to relieve torsional strain while maintaining acceptable angles
• It becomes aromatic to relieve strain
• It converts to an open chain under normal conditions
• It forms transannular hydrogen bonds making it planar

Correct Answer: It adopts an envelope conformation to relieve torsional strain while maintaining acceptable angles

Q19. Baeyer’s strain theory cannot predict conformational energy barriers because it neglects:

• Only bond lengths changes
• Torsional interactions and dynamic processes like ring flipping
• Atomic masses in the ring
• The presence of water as solvent

Correct Answer: Torsional interactions and dynamic processes like ring flipping

Q20. Why is cyclohexane considered strain-free in many contexts despite small deviations from 109.5°?

• Because cyclohexane has extensive conjugation
• Chair conformation minimizes both angle and torsional strain making net strain very low
• Because ring opening is instantaneous at room temperature
• Because it contains heteroatoms neutralizing strain

Correct Answer: Chair conformation minimizes both angle and torsional strain making net strain very low

Q21. What experimental evidence supports the idea of increased s-character in cyclopropane C–C bonds, contradicting Baeyer’s angle-only view?

• Infrared absorption identical to ethane
• Shorter C–C bond lengths and higher bond energies consistent with increased s-character
• No observable differences in bond parameters
• Cyclopropane being planar like benzene

Correct Answer: Shorter C–C bond lengths and higher bond energies consistent with increased s-character

Q22. Which limitation of Baeyer’s theory affects the prediction of reactivity of small rings?

• It predicts reactivity solely from electronic delocalization
• It ignores orbital strain, angle/pyramidalization and bent bonds which affect ring opening reactivity
• It assumes all small rings are unreactive
• It focuses only on aromatic stabilization

Correct Answer: It ignores orbital strain, angle/pyramidalization and bent bonds which affect ring opening reactivity

Q23. How does Baeyer’s theory treat heterocycles compared to what is observed experimentally?

• It accurately predicts heterocycle stability using only angle strain
• It underestimates the role of heteroatom hybridization, lone-pair repulsion and bond angles, leading to errors
• It predicts heterocycles are always aromatic
• It states heteroatoms eliminate all ring strain

Correct Answer: It underestimates the role of heteroatom hybridization, lone-pair repulsion and bond angles, leading to errors

Q24. Which statement about ring puckering is inconsistent with Baeyer’s planar assumption?

• Puckering relieves torsional strain and is common in 4–7 membered rings
• Puckering increases angle strain only
• Puckering is irrelevant to ring stability
• Puckering eliminates all chemical reactivity

Correct Answer: Puckering relieves torsional strain and is common in 4–7 membered rings

Q25. Which phenomenon in medium rings is not predicted by Baeyer’s model but is significant experimentally?

• Complete planarity of medium rings
• Transannular (through-space) strain and interactions affecting stability and reactivity
• Absence of any steric effects
• Instantaneous conversion to aromatic compounds

Correct Answer: Transannular (through-space) strain and interactions affecting stability and reactivity

Q26. In conformational analysis, which energy term did Baeyer neglect that is now considered crucial?

• Bond dissociation energy
• Torsional energy from eclipsing interactions between bonds
• Mass defect energy
• Optical rotation energy

Correct Answer: Torsional energy from eclipsing interactions between bonds

Q27. Which observation about substituted cyclohexanes posed a challenge to Baeyer’s predictions?

• Substituents always prefer axial positions
• Bulky substituents prefer equatorial positions due to steric and torsional effects
• Substituents eliminate ring flipping entirely
• Substituted cyclohexanes are always planar

Correct Answer: Bulky substituents prefer equatorial positions due to steric and torsional effects

Q28. Which structural feature of bicyclic systems influences strain but is not addressed by Baeyer’s simple model?

• The molecular weight of the bicyclic molecule
• Bridgehead geometry and constraints affecting bond angles and hybridization
• Only the number of hydrogens present
• The color of the compound

Correct Answer: Bridgehead geometry and constraints affecting bond angles and hybridization

Q29. Why is the concept of “torsional strain” critical when improving on Baeyer’s theory?

• Because it replaces angle strain entirely
• Because torsional strain accounts for energy penalties due to eclipsed bonds ignored by angle-only models
• Because torsional strain is only relevant for liquids
• Because torsional strain eliminates need for experimental data

Correct Answer: Because torsional strain accounts for energy penalties due to eclipsed bonds ignored by angle-only models

Q30. Which of the following is a limitation of Baeyer’s approach when applied to polycyclic natural products relevant to drug design?

• It predicts accurate solubility properties
• It ignores cumulative steric, torsional and transannular strain and stereoelectronic effects important for bioactivity
• It always predicts metabolic stability correctly
• It accounts fully for hydrogen bonding interactions with proteins

Correct Answer: It ignores cumulative steric, torsional and transannular strain and stereoelectronic effects important for bioactivity

Q31. Which molecular orbital concept helps explain bonding in small rings beyond Baeyer’s model?

• Delocalized π-bonding identical to benzene
• Bent (banana) bond description and increased p-character hybridization in small rings
• Complete ionic character of C–C bonds
• Non-bonding orbitals dominate bonding

Correct Answer: Bent (banana) bond description and increased p-character hybridization in small rings

Q32. Baeyer’s theory would struggle to rationalize which heat of combustion trend?

• Higher heat of combustion per CH2 unit for cyclohexane compared to cyclopropane
• Lower heat of combustion per CH2 unit for cyclohexane indicating lower strain
• Identical heats for all cycloalkanes
• Heats of combustion irrelevant to strain assessment

Correct Answer: Lower heat of combustion per CH2 unit for cyclohexane indicating lower strain

Q33. Which experimental technique directly reveals nonplanar conformations that Baeyer’s planar model misses?

• Melting point measurement
• X-ray crystallography and NMR conformational analysis
• Paper chromatography

Correct Answer: X-ray crystallography and NMR conformational analysis

Q34. How does heteroatom incorporation in rings challenge the Baeyer model?

• Heteroatoms always decrease ring strain by making rings planar
• Heteroatoms change bond angles, hybridization and lone-pair repulsions that are not predicted by angle-only theory
• Heteroatoms make rings indistinguishable from alkanes
• Baeyer’s model fully accounts for heteroatoms automatically

Correct Answer: Heteroatoms change bond angles, hybridization and lone-pair repulsions that are not predicted by angle-only theory

Q35. Which limitation explains why Baeyer’s model cannot predict stereochemical outcomes in ring-forming reactions?

• It ignores kinetic vs thermodynamic control and stereoelectronic effects during bond formation
• It assumes all reactions are photochemical
• It only applies to gas-phase radical reactions
• It predicts stereochemistry purely from atomic weights

Correct Answer: It ignores kinetic vs thermodynamic control and stereoelectronic effects during bond formation

Q36. Which property of cyclopropane contributes to its unique chemistry and is omitted by Baeyer?

• Ability to freely rotate around C–C bonds
• High ring strain associated with bent bonds and unusual orbital interactions leading to ring-opening reactivity
• Extremely low bond energies making it inert
• Full aromatic stabilization like benzene

Correct Answer: High ring strain associated with bent bonds and unusual orbital interactions leading to ring-opening reactivity

Q37. Which term best captures the combined effects Baeyer failed to include for accurate ring strain evaluation?

• Only angle distortion
• Net strain energy comprising angle strain, torsional strain, steric interactions, and electronic effects
• Only molecular weight effects
• Only solvation effects

Correct Answer: Net strain energy comprising angle strain, torsional strain, steric interactions, and electronic effects

Q38. Why is Baeyer’s theory insufficient for predicting conformations of substituted cyclopentanes?

• Substituted cyclopentanes are always planar by default
• Because envelope and half-chair conformations, torsional effects and steric interactions determine preferred geometry
• Because all substituents convert cyclopentane into cyclohexane
• Because cyclopentane is aromatic

Correct Answer: Because envelope and half-chair conformations, torsional effects and steric interactions determine preferred geometry

Q39. What concept introduced after Baeyer helps explain why six-membered rings are unusually stable?

• Aromaticity of cyclohexane
• Conformational flexibility allowing chair conformation that minimizes both torsional and angle strain
• Complete ionic character of ring bonds
• Instant polymerization tendency

Correct Answer: Conformational flexibility allowing chair conformation that minimizes both torsional and angle strain

Q40. Which experimental observation on bicyclic systems cannot be rationalized by Baeyer’s model?

• Similar heats of combustion for all bicyclic isomers
• Different stabilities and reactivities due to bridgehead angle distortion and constrained hybridization
• Exclusive formation of planar structures in all cases
• Absence of any strain-related differences

Correct Answer: Different stabilities and reactivities due to bridgehead angle distortion and constrained hybridization

Q41. How does the concept of pyramidalization at carbon atoms refine our understanding beyond Baeyer’s assumptions?

• Pyramidalization only applies to nitrogen atoms
• Pyramidalization alters orbital hybridization and bonding geometry, affecting reactivity and strain beyond simple angle deviation
• Pyramidalization is irrelevant to ring strain
• Pyramidalization makes all rings planar

Correct Answer: Pyramidalization alters orbital hybridization and bonding geometry, affecting reactivity and strain beyond simple angle deviation

Q42. Which limitation of Baeyer’s theory becomes critical when analyzing drug-like polycyclic scaffolds?

• It perfectly predicts ADME properties
• It ignores stereoelectronic effects, conformational ensembles and local strain that influence binding and metabolism
• It accounts fully for hydrogen bonding in enzyme pockets
• It provides accurate pKa predictions

Correct Answer: It ignores stereoelectronic effects, conformational ensembles and local strain that influence binding and metabolism

Q43. Baeyer’s model fails to explain why some large rings cyclize readily while others do not because it ignores:

• Only the ring entropy term in cyclization kinetics and transannular strain
• Only the color of the reactants
• Only the presence of oxygen
• Nothing; it predicts all cyclizations accurately

Correct Answer: Only the ring entropy term in cyclization kinetics and transannular strain

Q44. Which concept is essential to reconcile Baeyer’s predictions with observed smaller-than-expected ring strain in cyclohexane?

• Delocalized π-electron cloud in cyclohexane
• Three-dimensional conformational freedom and torsional relief in the chair form
• Full ionization of carbon atoms
• Permanent planarity enforced by resonance

Correct Answer: Three-dimensional conformational freedom and torsional relief in the chair form

Q45. Which statement about the predictive scope of Baeyer’s strain theory is accurate?

• It accurately predicts all chemical properties of cyclic compounds
• It is a useful historical model for angle-related strain but insufficient for complete strain-energy analysis
• It is the only theory currently used in medicinal chemistry
• It explains electronic spectra of rings fully

Correct Answer: It is a useful historical model for angle-related strain but insufficient for complete strain-energy analysis

Q46. What role do stereoelectronic effects play that Baeyer’s model overlooks?

• Stereoelectronic effects are negligible in rings
• Stereoelectronic effects influence preferred conformations and reaction trajectories, affecting stability and reactivity
• Stereoelectronic effects only affect ionic salts
• Stereoelectronic effects prevent any ring conformational changes

Correct Answer: Stereoelectronic effects influence preferred conformations and reaction trajectories, affecting stability and reactivity

Q47. In the context of Baeyer’s theory, what is the significance of ring flipping in cyclohexane?

• Ring flipping has nothing to do with strain and was predicted by Baeyer
• Ring flipping demonstrates dynamic conformational equilibrium between low-energy forms, a phenomenon Baeyer did not anticipate
• Ring flipping converts cyclohexane into cyclohexene
• Ring flipping destroys all substituents on the ring

Correct Answer: Ring flipping demonstrates dynamic conformational equilibrium between low-energy forms, a phenomenon Baeyer did not anticipate

Q48. Which theoretical advance allowed chemists to quantify torsional contributions absent in Baeyer’s work?

• Classical valence bond theory only
• Conformational analysis incorporating Newman projections, torsional energy terms and computational methods
• Only mass spectrometry advances
• Early chromatography techniques

Correct Answer: Conformational analysis incorporating Newman projections, torsional energy terms and computational methods

Q49. How does ring fusion in polycyclic aromatic systems illustrate a limitation of Baeyer’s theory when heteroatoms or unsaturation are present?

• Baeyer’s model fully accounts for fused aromatic systems with heteroatoms
• Ring fusion and conjugation alter electronic distribution, hybridization and planarity in ways Baeyer’s angle-only model cannot predict
• Fused systems always behave like saturated cyclohexanes
• Fused rings eliminate all torsional strain by default

Correct Answer: Ring fusion and conjugation alter electronic distribution, hybridization and planarity in ways Baeyer’s angle-only model cannot predict

Q50. For a B. Pharm student, what is the best summary of Baeyer’s strain theory limitations?

• It comprehensively explains modern conformational and electronic effects in drug molecules
• It provides historical insight into angle strain but omits torsional strain, stereoelectronic effects, bent bonds and conformational dynamics crucial for drug design
• It proves all rings are unstable and cannot exist
• It is only applicable to inorganic chemistry

Correct Answer: It provides historical insight into angle strain but omits torsional strain, stereoelectronic effects, bent bonds and conformational dynamics crucial for drug design

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