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Questions and Answers
What is the effect of a polar solvent in an SN1 reaction?
What is the effect of a polar solvent in an SN1 reaction?
- It stabilizes the carbocation (correct)
- It facilitates the nucleophile
- It creates a solvent shell around the counter-ion
- It slows down the reaction
Which of the following factors is the most important in determining the mechanism of an alkyl halide reaction?
Which of the following factors is the most important in determining the mechanism of an alkyl halide reaction?
- Substrate structure (correct)
- Leaving group ability
- Strength of the nucleophile
- Solvent polarity
What is the difference between polar protic and polar aprotic solvents?
What is the difference between polar protic and polar aprotic solvents?
- Polar aprotic solvents are used in SN1 reactions, while polar protic solvents are used in SN2 reactions
- Polar aprotic solvents are used in elimination reactions, while polar protic solvents are used in substitution reactions
- Polar protic solvents are stronger than polar aprotic solvents
- Polar protic solvents can H-bond, while polar aprotic solvents cannot (correct)
What is the role of the solvent in an SN2 reaction?
What is the role of the solvent in an SN2 reaction?
What type of carbocation is formed in the SN1 mechanism of an allylic halide?
What type of carbocation is formed in the SN1 mechanism of an allylic halide?
What is the major product of an elimination reaction when a sterically hindered base is used?
What is the major product of an elimination reaction when a sterically hindered base is used?
Which of the following is a characteristic of a good leaving group in an alkyl halide reaction?
Which of the following is a characteristic of a good leaving group in an alkyl halide reaction?
What is the effect of a strong nucleophile on the mechanism of an alkyl halide reaction?
What is the effect of a strong nucleophile on the mechanism of an alkyl halide reaction?
What is the mechanism of an E2 reaction?
What is the mechanism of an E2 reaction?
What determines the major product in an elimination reaction?
What determines the major product in an elimination reaction?
What is the purpose of protonating a leaving group in an alkyl halide reaction?
What is the purpose of protonating a leaving group in an alkyl halide reaction?
Which of the following types of halides is most likely to undergo an SN1 mechanism?
Which of the following types of halides is most likely to undergo an SN1 mechanism?
What is the primary function of T-BuO- in Alkyl Halide Reactions?
What is the primary function of T-BuO- in Alkyl Halide Reactions?
What is the most likely mechanism for an alkyl halide reaction at high temperature?
What is the most likely mechanism for an alkyl halide reaction at high temperature?
What is the primary consideration when determining the function of a reagent in Alkyl Halide Reactions?
What is the primary consideration when determining the function of a reagent in Alkyl Halide Reactions?
What is the most important factor in predicting the regiochemical and stereochemical outcome of an Alkyl Halide Reaction?
What is the most important factor in predicting the regiochemical and stereochemical outcome of an Alkyl Halide Reaction?
What is the primary difference between a 1° and 3° alkyl halide substrate?
What is the primary difference between a 1° and 3° alkyl halide substrate?
What is the role of hyperconjugation in elimination regioselectivity?
What is the role of hyperconjugation in elimination regioselectivity?
What is the outcome of an elimination reaction when the b carbon has only 1 proton?
What is the outcome of an elimination reaction when the b carbon has only 1 proton?
What is the overall goal of the three-step approach to Alkyl Halide Reactions?
What is the overall goal of the three-step approach to Alkyl Halide Reactions?
What is the requirement for the proton and the leaving group during an elimination reaction?
What is the requirement for the proton and the leaving group during an elimination reaction?
What is the purpose of determining the function of the reagent in alkyl halide reactions?
What is the purpose of determining the function of the reagent in alkyl halide reactions?
What is the goal of alkyl halide reactions?
What is the goal of alkyl halide reactions?
What is the role of sterically hindered bases in elimination regioselectivity?
What is the role of sterically hindered bases in elimination regioselectivity?
What is the outcome of a reaction influenced by?
What is the outcome of a reaction influenced by?
What is favored at high temperatures?
What is favored at high temperatures?
What is promoted by a polar aprotic solvent?
What is promoted by a polar aprotic solvent?
What is the role of a good leaving group in a reaction?
What is the role of a good leaving group in a reaction?
What is important to predict in a reaction?
What is important to predict in a reaction?
What factors influence the regiochemical outcome of a reaction?
What factors influence the regiochemical outcome of a reaction?
Study Notes
Substitution (SN2) Product
- Predict all products of a reaction and identify major and minor products considering function of reagent, type of substrate, and regiochemical and stereochemical outcome.
SN1 vs. SN2
- High temperature favors E1
- Good leaving group promotes SN2 reaction
- Polar aprotic solvent promotes SN2 reaction
- Polar solvent stabilizes carbocation in SN1
- Polar solvent facilitates nucleophile in SN2
- SN1 mechanism: δ+ δ- (OTs) (OMs)
- SN2 mechanism: δδ+ δ+ δ- δδ+ δ+ δ-
- Polar protic solvent promotes SN1 reaction
- Polar aprotic solvent promotes SN2 reaction
Elimination Reaction
- Major product: Zaitsev product (more substituted alkene)
- Minor product: Hofmann product (less substituted alkene)
- Sterically hindered/Bulky bases produce Hofmann product as major product
- Elimination regioselectivity: controlled by careful choice of base
- Elimination stereoselectivity: consider possibility of two stereoisomeric products
Alkyl Halide Reactions
- Nomenclature, types, physical properties, and reactions of alkyl halides
- Substitution reaction: SN2 (concerted mechanism) and SN1 (step-wise mechanism)
- Inversion of configuration and substitution stereochemistry in SN2 mechanism
- Identify leaving groups that are benzylic or allylic: undergo SN1 mechanism
- Strength of nucleophile (nucleophilicity ≈ polarizability ≈ atomic size)
- Strong nucleophile favors SN2; weak favors SN1
- Good leaving group: conjugate base of a strong acid is stable
Predicting Reactions
- Determine function of reagent: is it more likely to act as a base, nucleophile, or both?
- Analyze substrate (1°, 2°, or 3°) and predict expected mechanism (SN1, SN2, E1, or E2)
- Consider regiochemistry and stereochemistry
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Description
Test your knowledge of alkyl halides, including nucleophilic substitution and elimination reactions, nomenclature, physical properties, and reaction mechanisms. Learn about SN2 and SN1 mechanisms, stereochemistry, and substrate structure. This quiz covers the key concepts in Chapter 5 of CHEM40.
