CHEM40 Chapter 5: Alkyl Halides Reactions

Questions and Answers

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?

Substrate structure (correct)

Leaving group ability

Strength of the nucleophile

Solvent polarity

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?

It facilitates the nucleophile Signup and view all the answers

What type of carbocation is formed in the SN1 mechanism of an allylic halide?

Resonance-stabilized carbocation Signup and view all the answers

What is the major product of an elimination reaction when a sterically hindered base is used?

Hofmann product Signup and view all the answers

Which of the following is a characteristic of a good leaving group in an alkyl halide reaction?

Stable conjugate base Signup and view all the answers

What is the effect of a strong nucleophile on the mechanism of an alkyl halide reaction?

Favors SN2 mechanism Signup and view all the answers

What is the mechanism of an E2 reaction?

Concerted mechanism Signup and view all the answers

What determines the major product in an elimination reaction?

The regioselectivity of the reaction Signup and view all the answers

What is the purpose of protonating a leaving group in an alkyl halide reaction?

To convert a bad leaving group into a good one Signup and view all the answers

Which of the following types of halides is most likely to undergo an SN1 mechanism?

Benzylic halide Signup and view all the answers

What is the primary function of T-BuO- in Alkyl Halide Reactions?

A base due to its high electronegativity Signup and view all the answers

What is the most likely mechanism for an alkyl halide reaction at high temperature?

E1 Signup and view all the answers

What is the primary consideration when determining the function of a reagent in Alkyl Halide Reactions?

The basicity of the reagent Signup and view all the answers

What is the most important factor in predicting the regiochemical and stereochemical outcome of an Alkyl Halide Reaction?

The type of substrate Signup and view all the answers

What is the primary difference between a 1° and 3° alkyl halide substrate?

Their size and branching Signup and view all the answers

What is the role of hyperconjugation in elimination regioselectivity?

To stabilize a neighboring sp2 carbon by delocalizing electron density Signup and view all the answers

What is the outcome of an elimination reaction when the b carbon has only 1 proton?

A stereospecific product with only one possible product Signup and view all the answers

What is the overall goal of the three-step approach to Alkyl Halide Reactions?

To predict the major and minor products Signup and view all the answers

What is the requirement for the proton and the leaving group during an elimination reaction?

They must be antiperiplanar Signup and view all the answers

What is the purpose of determining the function of the reagent in alkyl halide reactions?

To predict whether substitution or elimination will predominate Signup and view all the answers

What is the goal of alkyl halide reactions?

To predict all products Signup and view all the answers

What is the role of sterically hindered bases in elimination regioselectivity?

To control the regiochemical outcome of the elimination reaction Signup and view all the answers

What is the outcome of a reaction influenced by?

Type of substrate and reagent Signup and view all the answers

What is favored at high temperatures?

E1 reaction Signup and view all the answers

What is promoted by a polar aprotic solvent?

SN2 reaction Signup and view all the answers

What is the role of a good leaving group in a reaction?

It promotes an SN2 reaction Signup and view all the answers

What is important to predict in a reaction?

Both the major and minor products Signup and view all the answers

What factors influence the regiochemical outcome of a reaction?

Function of the reagent and type of substrate Signup and view all the answers

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.