E2 reaction – kinetics MCQs With Answer

E2 reaction – kinetics MCQs With Answer provides B. Pharm students a concise, exam-focused introduction to bimolecular elimination kinetics. This guide covers the E2 mechanism, rate law (second-order), effects of base strength, substrate structure, leaving-group ability, solvent influence, stereochemistry (anti-periplanar requirement), and temperature dependence. Designed for pharmacy undergraduates, the content links mechanistic insights to practical problems such as predicting product regioselectivity (Zaitsev vs Hofmann), kinetic isotope effects, and experimental rate determination. Clear explanations and targeted practice reinforce concepts needed for organic chemistry and medicinal chemistry courses. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the rate law for a typical E2 reaction?

• Rate = k[substrate]
• Rate = k[base]
• Rate = k[substrate][base]
• Rate = k[substrate]^2

Correct Answer: Rate = k[substrate][base]

Q2. E2 reactions are best described as which type of mechanism?

• Two-step, via carbocation intermediate
• Concerted, single-step bond-making and bond-breaking
• Radical chain mechanism
• Nucleophilic addition-elimination

Correct Answer: Concerted, single-step bond-making and bond-breaking

Q3. Which factor increases the rate of an E2 reaction most significantly?

• Weak, bulky base
• Strong, non-nucleophilic base
• Strong, unhindered base
• Very poor leaving group

Correct Answer: Strong, unhindered base

Q4. For E2 reactions which substrate is most likely to undergo elimination rapidly?

• Primary with a weak base
• Primary with a strong base
• Tertiary with a weak base
• Methyl substrate

Correct Answer: Primary with a strong base

Q5. The stereochemical requirement often necessary for E2 is:

• Syn-periplanar hydrogen and leaving group
• Anti-periplanar hydrogen and leaving group
• No stereochemical requirement
• Perpendicular arrangement

Correct Answer: Anti-periplanar hydrogen and leaving group

Q6. Which solvent normally accelerates an E2 reaction when using an ionic base?

• Polar protic solvent
• Polar aprotic solvent
• Nonpolar solvent
• Superacidic solvent

Correct Answer: Polar aprotic solvent

Q7. In competition between E2 and SN2 on a secondary substrate, which condition favors E2?

• Use of a weak nucleophile at low temperature
• Use of a strong, bulky base
• Use of a small, strong nucleophile in polar aprotic solvent
• Use of a neutral solvent and moderate nucleophile

Correct Answer: Use of a strong, bulky base

Q8. Which leaving group property promotes faster E2 reactions?

• Poor leaving ability (e.g., –OH without activation)
• Good leaving ability (e.g., I–, Br–)
• Neutral, nonpolar leaving group
• Strongly basic leaving group

Correct Answer: Good leaving ability (e.g., I–, Br–)

Q9. The E2 transition state is best described as:

• Fully charged carbocation
• Partial bond cleavage and partial bond formation
• Radical pair
• Stable intermediate

Correct Answer: Partial bond cleavage and partial bond formation

Q10. Increasing temperature generally affects E2 rates by:

• Decreasing the rate due to entropic penalties
• Increasing the rate by providing activation energy
• No effect on rate
• Converting mechanism to E1 only

Correct Answer: Increasing the rate by providing activation energy

Q11. A primary substrate with a bulky base often gives which elimination product preference?

• Zaitsev product exclusively
• Hofmann product predominance
• Equal Zaitsev and Hofmann
• No elimination occurs

Correct Answer: Hofmann product predominance

Q12. Which experimental observation indicates an E2 mechanism rather than E1?

• Rate depends only on substrate concentration
• Rate depends on both substrate and base concentrations
• Formation of a rearranged product via carbocation
• Reaction proceeds only at high temperature

Correct Answer: Rate depends on both substrate and base concentrations

Q13. A primary kinetic isotope effect (KIE) observed when replacing β-hydrogen with deuterium suggests what about the E2 reaction?

• β-hydrogen removal is not involved in rate-determining step
• β-hydrogen removal is involved in the rate-determining step
• Reaction proceeds via carbocation
• Deuterium increases rate dramatically

Correct Answer: β-hydrogen removal is involved in the rate-determining step

Q14. Which substrate geometry issue can prevent E2 elimination from occurring readily?

• Anti-periplanar H and leaving group alignment
• Stereochemical lock that prevents anti-periplanar alignment
• Presence of a good leaving group
• Planar sp2 center adjacent to leaving group

Correct Answer: Stereochemical lock that prevents anti-periplanar alignment

Q15. Hammett plots applied to E2 kinetics provide information about:

• Solvent polarity only
• Electronic effects of substituents on reaction rate
• Steric hindrance exclusively
• Activation entropy alone

Correct Answer: Electronic effects of substituents on reaction rate

Q16. How does a better leaving group affect the activation energy for E2?

• Raises activation energy
• Lowers activation energy
• Has no effect
• Makes reaction endothermic only

Correct Answer: Lowers activation energy

Q17. Under pseudo-first-order conditions in E2 kinetics, which is true?

• Both concentrations are kept equal
• One reactant (usually base) is in large excess
• Reaction becomes unimolecular by mechanism
• Rate law switches to third order

Correct Answer: One reactant (usually base) is in large excess

Q18. Which spectroscopic or analytical method is commonly used to measure E2 reaction rates?

• Mass spectrometry of gas-phase radicals only
• Time-resolved NMR or UV-Vis to follow concentration changes
• X-ray crystallography of intermediates
• IR spectroscopy of solid samples only

Correct Answer: Time-resolved NMR or UV-Vis to follow concentration changes

Q19. A tertiary alkyl halide with a weak base and polar protic solvent most likely follows:

• E2 mechanism
• SN2 mechanism
• E1 mechanism
• Radical substitution

Correct Answer: E1 mechanism

Q20. Which statement about regioselectivity in E2 is correct?

• E2 always gives the less substituted alkene
• Bulky bases can favor less substituted (Hofmann) alkenes
• Leaving group size controls product entirely
• Stereochemistry has no effect on regioselectivity

Correct Answer: Bulky bases can favor less substituted (Hofmann) alkenes

Q21. The Hammond postulate applied to E2 transition states suggests:

• Transition state resembles reactants if reaction is exothermic
• Transition state resembles products if reaction is exothermic
• Transition state always resembles products
• Hammond postulate is not applicable to E2

Correct Answer: Transition state resembles reactants if reaction is exothermic

Q22. In an E2 reaction, what role does a polar aprotic solvent play on base strength?

• It solvates anions strongly, decreasing base strength
• It poorly solvates anions, enhancing base/nucleophile strength
• It converts base into its conjugate acid
• It always favors SN1 over E2

Correct Answer: It poorly solvates anions, enhancing base/nucleophile strength

Q23. Which observation would indicate a concerted E2 pathway from kinetic experiments?

• Presence of a discrete intermediate detected spectroscopically
• Second-order dependence on reactants and no intermediate
• Rate independent of base concentration
• Formation of rearranged products

Correct Answer: Second-order dependence on reactants and no intermediate

Q24. A syn-periplanar geometry can sometimes give E2 product when:

• Anti-periplanar geometry is mandatory without exception
• Conformational constraints force syn elimination and base is strong
• Leaving group is very poor
• Solvent is nonpolar

Correct Answer: Conformational constraints force syn elimination and base is strong

Q25. Which of the following bases is most likely to favor E2 over SN2 on a secondary substrate?

• Azide ion (N3–)
• Cyanide (CN–)
• Tertiary butoxide (t-BuO–)
• Methoxide (MeO–)

Correct Answer: Tertiary butoxide (t-BuO–)

Q26. The kinetic isotope effect (KIE) in E2 usually arises because:

• Substitution of H with D changes substrate polarity
• C–H bond cleavage is involved in the rate-determining step and D forms a stronger bond
• Deuterium changes the leaving-group ability
• KIE is not observable in E2 reactions

Correct Answer: C–H bond cleavage is involved in the rate-determining step and D forms a stronger bond

Q27. Which statement about E2 and stereospecificity is true?

• E2 is not stereospecific and gives racemization
• E2 is stereospecific and depends on relative stereochemistry of H and leaving group
• E2 always inverts stereochemistry at the reacting center
• E2 always retains stereochemistry

Correct Answer: E2 is stereospecific and depends on relative stereochemistry of H and leaving group

Q28. Which pair of factors most favors E2 over E1?

• Weak base and polar protic solvent
• Strong base and low substrate concentration
• Strong base and polar aprotic solvent
• High temperature and poor leaving group

Correct Answer: Strong base and polar aprotic solvent

Q29. For an E2 reaction, the observed activation parameters (ΔH‡ and ΔS‡) typically indicate:

• Large positive ΔS‡ characteristic of molecularity increase
• Negative ΔS‡ due to ordered transition state involving two species
• No definable activation parameters
• Activation entropy always zero

Correct Answer: Negative ΔS‡ due to ordered transition state involving two species

Q30. Which experimental change would convert an E2-dominated reaction into predominantly E1?

• Using a stronger base
• Changing solvent to polar protic and increasing temperature
• Making base concentration very high
• Switching to polar aprotic solvent

Correct Answer: Changing solvent to polar protic and increasing temperature

Q31. Neighboring group participation can influence E2 kinetics by:

• Never participating in elimination
• Stabilizing a transition state or forming bridged intermediates that alter rate
• Always slowing down the reaction
• Changing reaction to radical mechanism

Correct Answer: Stabilizing a transition state or forming bridged intermediates that alter rate

Q32. In kinetic studies of E2, plotting ln(rate) vs 1/T gives information according to:

• Michaelis-Menten equation
• Arrhenius equation to determine activation energy
• Henderson-Hasselbalch equation
• van’t Hoff equation for equilibria only

Correct Answer: Arrhenius equation to determine activation energy

Q33. Which is true about the concerted nature of E2 and bond orders in the transition state?

• C–H bond broken fully before C–X bond breaks
• C–X bond is broken fully before C–H bond forms
• Both bonds are partially broken/formed simultaneously
• No bonds change during transition

Correct Answer: Both bonds are partially broken/formed simultaneously

Q34. A substrate with β-branching that restricts anti-periplanar conformation will:

• Always undergo faster E2
• Possibly slow down E2 or change stereochemical outcome
• Favor SN2 exclusively
• Not be affected in reaction rate or pathway

Correct Answer: Possibly slow down E2 or change stereochemical outcome

Q35. Which effect does increasing ionic strength of the medium have on bimolecular ionic reactions like E2?

• Always decreases the rate drastically
• Can influence rate by screening charges and altering effective concentrations
• Has no effect on ionic reactions
• Converts mechanism to unimolecular

Correct Answer: Can influence rate by screening charges and altering effective concentrations

Q36. In an intramolecular E2, ring constraints often lead to:

• Faster rate due to favorable geometry and lower entropic cost
• No elimination possible
• Always E1 mechanism instead
• Random product distribution

Correct Answer: Faster rate due to favorable geometry and lower entropic cost

Q37. Which effect would a highly polar protic solvent have on a charged base in E2?

• It would increase base nucleophilicity dramatically
• It would solvate and decrease effective base strength
• It would have no effect on reactivity
• It would convert base into radical

Correct Answer: It would solvate and decrease effective base strength

Q38. The observed second-order rate constant for an E2 reaction doubles when base concentration doubles. This is consistent with:

• First-order dependence on base
• Zero-order dependence on base
• Second-order dependence on base
• Rate independent of base

Correct Answer: First-order dependence on base

Q39. Which of the following substituents on the β-carbon would generally speed up an E2 reaction?

• Electron-donating alkyl groups that stabilize developing negative character on hydrogen
• Electron-withdrawing groups that destabilize transition state
• A bulky group that prevents anti-periplanar alignment always
• No substituents makes it fastest

Correct Answer: Electron-donating alkyl groups that stabilize developing negative character on hydrogen

Q40. Competition experiments for E2 vs SN2 often change product ratios by altering:

• Temperature only
• Base strength, steric bulk, and solvent
• Isotope composition exclusively
• Concentration of inert salts only

Correct Answer: Base strength, steric bulk, and solvent

Q41. The term “bimolecular elimination” implies what about the transition state?

• Two molecules are involved in the rate-determining step
• Only one molecule is involved
• Many molecules aggregate before reaction
• Reaction occurs via radical intermediates

Correct Answer: Two molecules are involved in the rate-determining step

Q42. If an E2 reaction shows a negative entropy of activation (ΔS‡ < 0), this indicates:

• A less ordered transition state than reactants
• A more ordered transition state due to bimolecular association
• No change in order between reactants and TS
• That the reaction is barrierless

Correct Answer: A more ordered transition state due to bimolecular association

Q43. In teaching kinetics to B. Pharm students, why is understanding E2 important?

• It only applies to petrochemical processes
• It helps predict drug metabolite formation and stability of molecules
• It is irrelevant to pharmaceutical chemistry
• It replaces the need to learn E1 mechanisms

Correct Answer: It helps predict drug metabolite formation and stability of molecules

Q44. Which structural feature of the substrate disfavors E2?

• Accessible β-hydrogen anti to leaving group
• Fully substituted carbon with no β-hydrogen
• Good leaving group present
• Flexible chain allowing anti alignment

Correct Answer: Fully substituted carbon with no β-hydrogen

Q45. In kinetic experiments, a linear plot of 1/[substrate] vs time suggests which order with respect to substrate?

• Zero order
• First order
• Second order
• Third order

Correct Answer: Second order

Q46. Which of these molecules would most readily undergo E2 to form an alkene?

• Methyl chloride with weak base
• Tertiary bromide with strong base
• Primary chloride with no β-hydrogen
• Substrate lacking any leaving group

Correct Answer: Tertiary bromide with strong base

Q47. In reaction kinetics, the pre-exponential factor (A) in the Arrhenius equation reflects:

• Only the activation energy
• Frequency of effective collisions and orientation factors
• Solvent polarity exclusively
• Change in Gibbs free energy

Correct Answer: Frequency of effective collisions and orientation factors

Q48. A secondary alkyl halide gives mostly E2 product when reacted with potassium tert-butoxide in tert-butanol because:

• Potassium tert-butoxide is a weak base
• Bulky base favors elimination and steric hindrance prevents SN2
• tert-Butanol is polar aprotic
• Secondary substrates never undergo SN2

Correct Answer: Bulky base favors elimination and steric hindrance prevents SN2

Q49. Rate-determining step in E2 is characterized by:

• Formation of a long-lived intermediate
• Concerted bond-breaking/forming transition state with highest energy
• Subsequent fast equilibrium before slow step
• No identifiable transition state

Correct Answer: Concerted bond-breaking/forming transition state with highest energy

Q50. For B. Pharm students, integrating E2 kinetics with medicinal chemistry helps to:

• Ignore metabolic pathways of drugs
• Predict elimination pathways, stability and optimize drug design
• Only design inert molecules
• Replace the need for pharmacokinetics studies

Correct Answer: Predict elimination pathways, stability and optimize 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