Mechanisms of addition, elimination and substitution reactions and pathway determination - One Line Questions

1. Which of the following is a characteristic feature of the SN2 transition state? — A trigonal bipyramidal arrangement around the central carbon.
2. In the electrophilic addition of halogens to alkenes, what is the nature of the intermediate formed? — A cyclic halonium ion
3. An E1cB reaction typically involves: — A strong base abstracting a proton from a carbon adjacent to a carbonyl group.
4. In a nucleophilic addition to a ketone, the intermediate formed after nucleophilic attack is: — A tetrahedral alkoxide ion
5. Which of the following is an example of a nucleophilic substitution reaction? — Reaction of methyl bromide with hydroxide ion
6. Which type of reaction involves the breaking of a sigma bond and the formation of a pi bond, often leading to the loss of a small molecule? — Elimination Reaction
7. In an addition-elimination mechanism for nucleophilic aromatic substitution, what is the rate-determining step? — Formation of the Meisenheimer complex.
8. Which intermediate is formed in an SN1 reaction? — Carbocation
9. What is the stereochemical outcome of an SN1 reaction on a chiral substrate? — Racemization.
10. Which of the following reagents would favor an SN1 reaction over an SN2 reaction? — Dilute H2O in acetone
11. The E1 mechanism is characterized by which of the following steps? — Formation of a carbocation intermediate followed by deprotonation.
12. What is the primary difference between E1 and E2 mechanisms regarding the role of the base? — E1 does not involve the base in the rate-determining step; E2 involves the base in the rate-determining step.
13. Consider the reaction of propene with HBr. What type of mechanism is primarily involved? — Electrophilic Addition
14. The reaction of an alkene with ozone followed by a reducing agent is an example of: — Oxidative Cleavage
15. The reaction of an aldehyde with HCN is an example of: — Nucleophilic Addition
16. Which of the following is a common characteristic of SN2 reactions? — Backside attack by the nucleophile.
17. Which of the following is a characteristic of the E1 mechanism? — First-order kinetics.
18. The regioselectivity of electrophilic addition to unsymmetrical alkenes is governed by which rule? — Markovnikov's Rule
19. What is the primary reason for the stability of tertiary carbocations compared to primary carbocations? — Both inductive effect and hyperconjugation.
20. Which of the following is NOT a characteristic of free radical substitution reactions? — Favored by polar solvents.
21. Which of the following is a characteristic of SN1 reactions involving tertiary alkyl halides? — Racemization.
22. In an electrophilic addition reaction to an alkene, what is the role of the electrophile? — It accepts electrons from the pi bond.
23. The addition of HX to an alkene follows Markovnikov's rule primarily because: — The proton adds to the carbon with more hydrogens, forming the more stable carbocation.
24. The formation of a more substituted alkene is predicted by which rule in elimination reactions? — Zaitsev's Rule
25. Which of the following is a common method for determining the mechanism of a reaction? — Measuring the reaction rate under different conditions (kinetics).
26. What is the rate-determining step in an E2 reaction? — Concerted removal of the leaving group and proton.
27. In a substitution reaction at a chiral center, if inversion of configuration occurs, what type of mechanism is most likely involved? — SN2
28. Consider the reaction of an alkyl halide with a strong, bulky base like potassium tert-butoxide. Which reaction pathway is favored? — E2
29. Which reaction mechanism involves the formation of a cyclic intermediate with a three-membered ring? — Electrophilic addition of halogens to alkenes
30. The reaction of an alkyl halide with sodium ethoxide in ethanol is most likely to proceed via which mechanism? — E2
31. Which reaction pathway is generally favored for primary alkyl halides with strong nucleophiles? — SN2
32. The dehydration of secondary or tertiary alcohols using a strong acid typically proceeds via which mechanism? — E1
33. The formation of a carbanion intermediate is characteristic of which type of reaction mechanism? — E1cB
34. The mechanism of the reaction of an alcohol with PBr3 to form an alkyl bromide typically proceeds via: — SN2 mechanism
35. The formation of a benzyne intermediate is characteristic of which type of reaction? — Elimination reaction on an aryl halide
36. The rearrangement of a carbocation to form a more stable carbocation is a characteristic feature of which reaction types? — SN1 and E1
37. Which factor most significantly influences the rate of an SN2 reaction? — Concentration of the substrate and nucleophile
38. Which of the following conditions would favor an SN1 reaction over an SN2 reaction for a secondary alkyl halide? — Weak nucleophile, protic solvent
39. Which type of reaction is responsible for the conversion of cyclohexene to cyclohexane? — Addition
40. In the reaction of an alkene with BH3 followed by H2O2/OH-, what is the overall transformation achieved? — Hydroboration-oxidation, leading to anti-Markovnikov addition of H2O.
41. What is the stereochemistry observed in an E2 elimination reaction when starting with a chiral substrate? — Anti-periplanar elimination
42. Which of the following is a consequence of the anti-periplanar requirement in E2 reactions? — The leaving group and beta-hydrogen must be on opposite sides of the C-C bond.
43. What is the primary driving force for nucleophilic addition to carbonyl compounds? — The increased electrophilicity of the carbonyl carbon.
44. The Hoffman elimination generally favors the formation of which product? — The least substituted alkene (Hoffman product)
45. The formation of a vinyl cation is generally unfavorable. This explains why direct nucleophilic substitution on vinyl halides is difficult. — This statement is true due to the difficulty of forming a vinyl cation.
46. What is the role of a catalyst in many addition reactions to alkenes? — To polarize the pi bond or the attacking reagent.
47. What is the primary role of the solvent in SN1 reactions? — To stabilize the carbocation intermediate.
48. Which of the following is a strong base and a good nucleophile, often favoring SN2 reactions? — Hydroxide ion (OH-)
49. Which of the following solvents would best favor an SN2 reaction? — Acetone (aprotic, polar)
50. In the mechanism of addition of H2O to an alkene in the presence of an acid catalyst, what species attacks the alkene first? — Proton (H+)
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