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Questions and Answers
Which of the following statements accurately describes the role of π-bonds in electrophilic aromatic substitution (EAS)?
Which of the following statements accurately describes the role of π-bonds in electrophilic aromatic substitution (EAS)?
Benzene reacts readily with bromine in the absence of a catalyst.
Benzene reacts readily with bromine in the absence of a catalyst.
False (B)
What is the general two-step mechanism involved in all electrophilic aromatic substitution (EAS) reactions?
What is the general two-step mechanism involved in all electrophilic aromatic substitution (EAS) reactions?
The two-step mechanism of EAS involves the formation of a sigma complex (intermediate) followed by the loss of a proton to regenerate the aromatic ring.
The reaction of benzene with bromine in the presence of a catalyst is an example of ______ aromatic substitution.
The reaction of benzene with bromine in the presence of a catalyst is an example of ______ aromatic substitution.
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Match the following electrophilic aromatic substitution (EAS) reactions with their respective electrophiles:
Match the following electrophilic aromatic substitution (EAS) reactions with their respective electrophiles:
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Which type of group is characterized by accelerating reaction rates in electrophilic aromatic substitution?
Which type of group is characterized by accelerating reaction rates in electrophilic aromatic substitution?
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Meta directors favor the formation of ortho and para regioisomers.
Meta directors favor the formation of ortho and para regioisomers.
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What is the primary effect of electron-donating groups in electrophilic aromatic substitution?
What is the primary effect of electron-donating groups in electrophilic aromatic substitution?
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Electron-withdrawing groups are considered __________ groups in electrophilic aromatic substitution.
Electron-withdrawing groups are considered __________ groups in electrophilic aromatic substitution.
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Match the following groups with their effects on reaction rate:
Match the following groups with their effects on reaction rate:
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What is a likely outcome when phenol reacts with bromine?
What is a likely outcome when phenol reacts with bromine?
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Strongly activating groups can lead to mono-substituted products during electrophilic aromatic substitution.
Strongly activating groups can lead to mono-substituted products during electrophilic aromatic substitution.
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What should anilines be converted to in order to conduct electrophilic aromatic substitution reactions effectively?
What should anilines be converted to in order to conduct electrophilic aromatic substitution reactions effectively?
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A Friedel-Crafts reaction will not occur if a ______-directing deactivator is present on the ring.
A Friedel-Crafts reaction will not occur if a ______-directing deactivator is present on the ring.
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Match the following groups with their role in electrophilic aromatic substitution:
Match the following groups with their role in electrophilic aromatic substitution:
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What is the active electrophile in the nitration reaction?
What is the active electrophile in the nitration reaction?
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Sulfonation of aromatics can be reversed using water.
Sulfonation of aromatics can be reversed using water.
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Which group is replaced by a sulfonic acid group in sulfonation?
Which group is replaced by a sulfonic acid group in sulfonation?
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The combination of SO3 and H2SO4 is called __________.
The combination of SO3 and H2SO4 is called __________.
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What type of catalyst is used in Friedel-Crafts alkylation?
What type of catalyst is used in Friedel-Crafts alkylation?
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Match the following terms with their definitions:
Match the following terms with their definitions:
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What type of hydrocarbons would be most suitable for Friedel-Crafts alkylations?
What type of hydrocarbons would be most suitable for Friedel-Crafts alkylations?
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Which of the following is a reaction that results in the formation of aromatic amines?
Which of the following is a reaction that results in the formation of aromatic amines?
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Which reaction mechanism involves the creation of a carbocation as an active electrophile?
Which reaction mechanism involves the creation of a carbocation as an active electrophile?
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Friedel-Crafts acylation can produce aromatic aldehydes.
Friedel-Crafts acylation can produce aromatic aldehydes.
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What is the result of carbocation rearrangements during Friedel-Crafts reactions?
What is the result of carbocation rearrangements during Friedel-Crafts reactions?
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Friedel-Crafts reactions use an __________ to form an acylium ion.
Friedel-Crafts reactions use an __________ to form an acylium ion.
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Match the following types of alkyl halides with their classification:
Match the following types of alkyl halides with their classification:
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Which of the following affects the rate and regioselectivity of SEAr reactions?
Which of the following affects the rate and regioselectivity of SEAr reactions?
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Acid protonation of an alkene results in the formation of a stable carbocation.
Acid protonation of an alkene results in the formation of a stable carbocation.
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What type of shift do carbocations undergo to achieve more stability?
What type of shift do carbocations undergo to achieve more stability?
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Which of the following groups is considered a strong activating ortho/para director?
Which of the following groups is considered a strong activating ortho/para director?
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Meta substitution in electrophilic aromatic substitution is favored due to resonance stabilization.
Meta substitution in electrophilic aromatic substitution is favored due to resonance stabilization.
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What type of directing groups contain electron-rich groups without a lone pair capable of delocalizing into the benzene ring?
What type of directing groups contain electron-rich groups without a lone pair capable of delocalizing into the benzene ring?
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Halogens are considered __________ directors in electrophilic aromatic substitution despite being deactivating.
Halogens are considered __________ directors in electrophilic aromatic substitution despite being deactivating.
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Match the activating groups with their characteristics:
Match the activating groups with their characteristics:
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Which statement about arenium ion stability is correct?
Which statement about arenium ion stability is correct?
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Moderately activating ortho/para directors do not contain lone pairs that can delocalize.
Moderately activating ortho/para directors do not contain lone pairs that can delocalize.
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Which type of directing group is characterized by having polar π bonds and an electronegative atom?
Which type of directing group is characterized by having polar π bonds and an electronegative atom?
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The _______ position is less stable due to resonance contributors that yield a positive charge next to an electron-withdrawing group.
The _______ position is less stable due to resonance contributors that yield a positive charge next to an electron-withdrawing group.
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Which of these factors does NOT contribute to the regioselectivity of electrophilic aromatic substitution reactions?
Which of these factors does NOT contribute to the regioselectivity of electrophilic aromatic substitution reactions?
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Study Notes
Introduction to Organic Chemistry II - CHEM 2021
- Course Information:
- Introductory Organic Chemistry II, Winter 2024, York University
- Instructor: Dr. Lana Hébert
Chapter 10: Synthesis Using Aromatic Materials
- Focuses on reactions involving aromatic compounds, specifically using aromatic materials in synthesis.
Aromatic Compounds Are Everywhere!
- Many biomolecules contain aromatic rings.
- Aromatic rings are important in active research areas.
- Examples of compounds containing aromatic rings include:
- chloramphenicol (antibiotic)
- mescaline (peyote cactus active agent)
- adrenaline (hormone)
- ephedrine (bronchodilator)
- epinephrine (stress response hormone)
- amphetamine (appetite suppressant)
- methamphetamine ("speed")
- saccharin (artificial sweetener)
- p-dichlorobenzene (mothballs, air fresheners)
- coronene
- hexa-peri-hexabenzocoronene
Electrophilic Aromatic Substitution (EAS)
- General two-step mechanism:
-
- Addition of an electrophile
-
- Elimination of a leaving group to restore aromaticity
-
- Substituents can affect the rate and position of substitution.
- Different substituents can either activate or deactivate the ring for subsequent EAS reactions.
Halogenation of Aromatics: X₂ + Lewis Acid
- Aromatic rings can be halogenated using halogens (Br₂ or Cl₂) and a Lewis acid catalyst.
- Lewis acid catalysis increases the electrophilicity of a halogen.
- The halogen reacts with the aromatic ring to form an arenium ion intermediate.
- The specific halogen in the Lewis acid often corresponds to the substituted halogen.
- Fluorine does not require a catalyst.
- Iodine requires an oxidant to create I+, e.g. HNO3 or CuCl2.
Nitration of Aromatics: HNO₃ + H₂SO₄
- Nitration involves replacing a hydrogen atom with a nitro group.
- Nitric acid (HNO3) and sulfuric acid (H2SO4) are components in this reaction.
- The active electrophile in this reaction is the nitronium ion (NO2+). The nitronium ion is generated from the dehydration of HNO3 using H2SO4.
Friedel-Crafts Alkylation: Alkyl Halide + AlCl₃
- Friedel-Crafts alkylation adds alkyl groups to aromatic rings.
- The Lewis acid AlCl₃ creates a carbocation as the electrophile. A carbocation intermediate is formed when the halogen group is lost.
Friedel-Crafts Acylation: Acyl Chloride + AlCl₃
- Friedel-Crafts acylation adds acyl groups to aromatic compounds.
- Acylium ion is the electrophile.
- Acylium ion is formed when the activated leaving group is lost.
Friedel-Crafts Acylation: Variations
- Friedel-Crafts acylation can use anhydrides instead of acid chlorides.
- Carbon monoxide can be used in synthesis of aromatic aldehydes, using a Gatterman-Koch reaction.
Directing groups in EAS
- Different functional groups can either activate or deactivate the aromatic ring.
- Activating groups increase the rate of electrophilic aromatic substitution.
- Deactivating groups decrease the rate of electrophilic aromatic substitution
- Ortho-para vs. meta directing
Strongly Activating Ortho/Para Directors
- Contain heteroatoms with lone pairs.
- Lone pairs can delocalize into the ring via resonance.
Moderately Activating Ortho/Para Directors
- Contain a heteroatom involved in cross-conjugation.
- Lone pairs are delocalized into a different 𝜋-system.
Weakly Activating Ortho/Para Directors
- Mostly alkyl groups.
- Electron donating ability is predominantly through sigma bonds (inductive).
- These groups are considered comparatively weak electron donors.
Activating Ortho/Para Directing Groups: Aromatic Rings
- Aromatic rings can stabilize the arenium ion intermediate.
- Resonance is not favorable due to loss of aromaticity and increased steric strain.
Deactivating Ortho/Para Directing Groups: Halogens
- Halogens are deactivating via induction (electron withdrawing since they are electronegative)
- Show ortho/para directing behavior since they possess lone pairs.
- Resonance effect is weak.
- Orbital overlap between 2p ring orbitals and lone pair p orbitals for Cl and Br is also poor.
Deactivating Meta Directing Groups
- Electron-withdrawing groups (EWGs) typically deactivate an aromatic ring towards EAS.
- EWGs typically favor meta-substitution because one resonance form having the positive charge next to an EWG is less stable.
- These groups often contain, but aren't limited to polar bonds attached to atoms.
Limitations of EAS Reaction
- Strongly activating groups can lead to over substitution.
- Deactivating groups may decrease reaction rate or prevent the reaction entirely.
Retrosynthetic Analysis in Aromatic Synthesis
- Method for planning synthesis by reversing the reaction sequence.
- Involves identifying the fragments where the targeted molecule originates
- Identifies reagents to form the targeted substituents
Order of Synthetic Operations
- Order of reactions is critical to target product success.
- Often one must separate o/p reaction products.
Worked Examples
- Various examples are presented showing reactions using different reagents and the mechanisms underlying different reactions in the synthesis of various compounds.
Class Questions
- Different class questions are included throughout to evaluate understanding of the concepts.
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Description
This quiz tests your understanding of electrophilic aromatic substitution (EAS) reactions, particularly the role of π-bonds and the effects of different substituents on reaction rates. You'll match reactions to their electrophiles and identify key concepts related to groups that influence EAS mechanisms. Perfect for organic chemistry students!
