Podcast
Questions and Answers
In electrophilic aromatic substitution (EAS) reactions, which step is typically the rate-determining step?
In electrophilic aromatic substitution (EAS) reactions, which step is typically the rate-determining step?
- Removal of a proton from the intermediate carbocation to restore aromaticity.
- Addition of the electrophile ($E^+$) to form the intermediate carbocation ($\sigma$-complex). (correct)
- Rearrangement of the carbocation intermediate.
- Formation of the electrophile ($E^+$). (correct)
Electrophilic aromatic substitution ($S_EAr$) reactions involve the addition of a nucleophile to an aromatic ring.
Electrophilic aromatic substitution ($S_EAr$) reactions involve the addition of a nucleophile to an aromatic ring.
False (B)
What type of intermediate is formed during the electrophilic aromatic substitution ($S_EAr$) mechanism after the electrophile attacks the aromatic ring?
What type of intermediate is formed during the electrophilic aromatic substitution ($S_EAr$) mechanism after the electrophile attacks the aromatic ring?
carbocation
The first step in the electrophilic aromatic substitution ($S_EAr$) mechanism involves the formation of an ______.
The first step in the electrophilic aromatic substitution ($S_EAr$) mechanism involves the formation of an ______.
Which of the following is a characteristic of the intermediate carbocation formed during electrophilic aromatic substitution (EAS)?
Which of the following is a characteristic of the intermediate carbocation formed during electrophilic aromatic substitution (EAS)?
Which characteristic of benzene primarily dictates that it undergoes substitution reactions rather than addition reactions?
Which characteristic of benzene primarily dictates that it undergoes substitution reactions rather than addition reactions?
Benzene readily undergoes addition reactions to break its aromaticity and form saturated hydrocarbons.
Benzene readily undergoes addition reactions to break its aromaticity and form saturated hydrocarbons.
What specific criterion related to electron count must a cyclic, planar, conjugated molecule satisfy to be considered aromatic, as described by Hückel's rule?
What specific criterion related to electron count must a cyclic, planar, conjugated molecule satisfy to be considered aromatic, as described by Hückel's rule?
Due to the delocalization of $\pi$ electrons, benzene undergoes reactions involving ______ rather than addition.
Due to the delocalization of $\pi$ electrons, benzene undergoes reactions involving ______ rather than addition.
Match the properties with their description regarding benzene:
Match the properties with their description regarding benzene:
Which of the following is the active electrophile in the nitration of benzene using a mixture of $HNO_3$ and $H_2SO_4$?
Which of the following is the active electrophile in the nitration of benzene using a mixture of $HNO_3$ and $H_2SO_4$?
The given reaction of nitration is reversible.
The given reaction of nitration is reversible.
Identify the catalyst used in both bromination and chlorination reactions as described.
Identify the catalyst used in both bromination and chlorination reactions as described.
In the mechanism of electrophilic aromatic substitution, $AlCl_3$ acts as a ______ acid.
In the mechanism of electrophilic aromatic substitution, $AlCl_3$ acts as a ______ acid.
What is the overall heat profile of the nitration reaction?
What is the overall heat profile of the nitration reaction?
Which of the following conditions favors desulfonation of benzene sulfonic acid?
Which of the following conditions favors desulfonation of benzene sulfonic acid?
Friedel-Crafts acylation reactions typically result in polyacylation due to the activating effect of the acyl group.
Friedel-Crafts acylation reactions typically result in polyacylation due to the activating effect of the acyl group.
What is a major disadvantage of Friedel-Crafts alkylation compared to acylation, regarding the number of alkyl groups added to the benzene ring?
What is a major disadvantage of Friedel-Crafts alkylation compared to acylation, regarding the number of alkyl groups added to the benzene ring?
In Friedel-Crafts alkylation, rearrangement of the alkyl group can occur due to the formation of a more stable ______.
In Friedel-Crafts alkylation, rearrangement of the alkyl group can occur due to the formation of a more stable ______.
Match the following reaction conditions/species with their role in aromatic reactions:
Match the following reaction conditions/species with their role in aromatic reactions:
What is the main difference between using a fuming mixture ($H_2SO_4 + SO_3$) and concentrated $H_2SO_4$ in a reaction?
What is the main difference between using a fuming mixture ($H_2SO_4 + SO_3$) and concentrated $H_2SO_4$ in a reaction?
The presence of $SO_3$ in a fuming mixture slows down the reaction compared to using concentrated $H_2SO_4$.
The presence of $SO_3$ in a fuming mixture slows down the reaction compared to using concentrated $H_2SO_4$.
What component in the fuming mixture distinguishes it from concentrated sulfuric acid, and how does this component affect the reaction rate?
What component in the fuming mixture distinguishes it from concentrated sulfuric acid, and how does this component affect the reaction rate?
The rate of reaction is ______ when using a fuming mixture ($H_2SO_4 + SO_3$) compared to using concentrated $H_2SO_4$.
The rate of reaction is ______ when using a fuming mixture ($H_2SO_4 + SO_3$) compared to using concentrated $H_2SO_4$.
What role does the addition of $SO_3$ play in the fuming mixture? (Select the BEST answer)
What role does the addition of $SO_3$ play in the fuming mixture? (Select the BEST answer)
Which of the following is a key reason for preferring acylation over direct alkylation in synthesizing monoalkyl benzene?
Which of the following is a key reason for preferring acylation over direct alkylation in synthesizing monoalkyl benzene?
The reduction step following acylation is necessary to convert the acyl group into an alkyl group.
The reduction step following acylation is necessary to convert the acyl group into an alkyl group.
What reagents are effectively used in the reduction step following acylation to obtain N-propyl benzene?
What reagents are effectively used in the reduction step following acylation to obtain N-propyl benzene?
To convert benzene to N-propyl benzene with 100% yield, acylation is followed by ______.
To convert benzene to N-propyl benzene with 100% yield, acylation is followed by ______.
What is the overall yield expected when converting benzene to N-propyl benzene using acylation followed by reduction, as indicated in the content?
What is the overall yield expected when converting benzene to N-propyl benzene using acylation followed by reduction, as indicated in the content?
Flashcards
What is a cyclic compound?
What is a cyclic compound?
A cyclic (ring-shaped) molecule with alternating single and double bonds.
What does conjugated mean in chemistry?
What does conjugated mean in chemistry?
A system with alternating single and multiple bonds, allowing electron delocalization.
Define planar.
Define planar.
A molecule where all atoms lie in the same plane.
What is Hückel's Rule?
What is Hückel's Rule?
A rule stating that a cyclic, planar molecule with (4n+2) π electrons is aromatic.
Signup and view all the flashcards
Why does benzene favor substitution?
Why does benzene favor substitution?
Benzene undergoes substitution reactions rather than addition reactions to maintain its aromaticity.
Signup and view all the flashcards
Electrophilic Aromatic Substitution (EAS)
Electrophilic Aromatic Substitution (EAS)
Reactions where an electrophile replaces a leaving group on an aromatic ring.
Signup and view all the flashcards
Formation of E+
Formation of E+
The first stage in EAS reactions; generates a strong electrophile.
Signup and view all the flashcards
E+ Addition: Carbocation Intermediate
E+ Addition: Carbocation Intermediate
The electrophile (E+) adds to the aromatic ring forming a carbocation intermediate.
Signup and view all the flashcards
Rate Determining Step in EAS
Rate Determining Step in EAS
The step where the rate of the entire EAS reaction is determined.
Signup and view all the flashcards
Sigma-Complex
Sigma-Complex
The carbocation intermediate formed after E+ addition, is usually called a sigma-complex.
Signup and view all the flashcards
Catalyst in Aromatic Substitution
Catalyst in Aromatic Substitution
A substance that speeds up a chemical reaction without being consumed. Common catalysts in aromatic substitution include $AlCl_3$ with $Br_2$ or $Cl_2$.
Signup and view all the flashcards
Electrophile in Bromination
Electrophile in Bromination
The electrophile ($E^+$) in bromination is $Br^+$, generated by the reaction of $Br_2$ with $AlCl_3$.
Signup and view all the flashcards
Electrophile in Nitration
Electrophile in Nitration
The electrophile ($E^+$) in nitration is $NO_2^+$, generated from the reaction of $HNO_3$ with $H_2SO_4$.
Signup and view all the flashcards
Nitration Reaction Characteristics
Nitration Reaction Characteristics
Nitration of benzene using $HNO_3$ and $H_2SO_4$ is irreversible and overall exothermic.
Signup and view all the flashcards
Sulfonation
Sulfonation
Sulfonation involves adding $SO_3H$ to benzene.
Signup and view all the flashcards
Sulfonation Reaction
Sulfonation Reaction
Reaction where sulfuric acid removes water from a product.
Signup and view all the flashcards
Friedel-Crafts Acylation
Friedel-Crafts Acylation
Attaching a carbonyl group (R-C=O) to an aromatic ring using an acyl halide and a Lewis acid catalyst.
Signup and view all the flashcards
Friedel-Crafts Alkylation
Friedel-Crafts Alkylation
Attaching an alkyl group to an aromatic ring using an alkyl halide and a Lewis acid catalyst.
Signup and view all the flashcards
Polyalkylation
Polyalkylation
Multiple alkyl groups attach to the aromatic ring during Friedel-Crafts alkylation.
Signup and view all the flashcards
Rearrangement in Alkylation
Rearrangement in Alkylation
When the carbon skeleton of the alkyl group rearranges during Friedel-Crafts alkylation.
Signup and view all the flashcards
Alkylation: No Poly/Rearrangement
Alkylation: No Poly/Rearrangement
Alkylation that avoids multiple attachments and structural changes.
Signup and view all the flashcards
What is a fuming mixture?
What is a fuming mixture?
A mixture of concentrated sulfuric acid ($H_2SO_4$) and sulfur trioxide ($SO_3$).
Signup and view all the flashcards
Conc. $H_2SO_4$ role in reactions?
Conc. $H_2SO_4$ role in reactions?
Concentrated sulfuric acid ($H_2SO_4$) alone, used to facilitate reactions, but more slowly than fuming mixtures.
Signup and view all the flashcards
Monoalkyl Benzene Goal
Monoalkyl Benzene Goal
A method to get a benzene ring with only one alkyl group attached.
Signup and view all the flashcards
Acylation First
Acylation First
Solve alkylation issues by first doing acylation.
Signup and view all the flashcards
Fuming mixture vs. Conc. $H_2SO_4$?
Fuming mixture vs. Conc. $H_2SO_4$?
Reactions using fuming mixtures occur faster than those using only concentrated $H_2SO_4$.
Signup and view all the flashcards
Role of $SO_3$ in fuming mixture?
Role of $SO_3$ in fuming mixture?
Sulfur trioxide ($SO_3$) presence in a fuming mixture enhances the mixture's reactivity compared to using concentrated $H_2SO_4$ alone.
Signup and view all the flashcards
+C-C Followed by Reduction
+C-C Followed by Reduction
Acylation followed by reduction.
Signup and view all the flashcards
Zn/Hg/HCl Reduction
Zn/Hg/HCl Reduction
Reagents used for reducing a carbonyl group to a methylene group.
Signup and view all the flashcards
First step in sulfonation?
First step in sulfonation?
The first step in sulfonation involves the addition of $SO_3$ to a substrate.
Signup and view all the flashcardsStudy Notes
- Benzene is cyclic and conjugated
- Benzene is planar
- Benzene follows Huckel's rule; therefore, it is aromatic
- Benzene undergoes substitution reactions due to the delocalization of pi electrons
Electrophilic Substitution Reactions (EAS / ESAr)
- Mechanism consists of 3 steps
Formation of E+ (electrophile)
Addition of E+ to form intermediate carbocation (sigma complex)
- This is the rate-determining step
Deprotonation regenerates aromatic system
- Addition of Y+ turns into sigma complex through resonance
- After the sigma complex is formed, HB is eliminated
Halogenation [halogen + Lewis acid]
- Polarize halogen molecule to form E+
- Cat. Cl2/AlCl3 (chlorination)
- Cat. Br2/AlCl3 (bromination)
- Cl2 + AlCl3 becomes Cl-AlCl3
- Benzene + Cl-AlCl3 results into the sigma complex Cl
- The sigma complex Cl turns into chlorobenzene + AlCl3 + Hcl through deprotonation
Nitration [HNO3 + H2SO4]
- H-O-NO2 + H-O-SO3H becomes H-O-NO2+H-OSO3H
- E+ is NO2
- Benzene + NO2 results into the sigma complex NO2
- The sigma complex NO2 turns into nitrobenzene through deprotonation in the presence of H2SO4 (lewis base)
- Reaction is irreversible
- Overall reaction is exothermic
Sulphonation & desulphonation
- Adds SO3H to benzene
- Fuming mixture is conc. H2SO4 + SO3 which provides fast reaction
- Conc. H2SO4 results in a slow reaction
- H-O-S-OH is sulfuric acid
- XS sulfuric acid (H2SO4) turns into the sigma complex SO3H which forms benzenesulfonic acid through deprotonation
- Reaction is reversible
- Sulphonation: Fuming mix
- Desulphonation: dil H2SO4/V.H2O
Friedel-Crafts Acylation
- R-C=O Cl + AlCl3 becomes R-C=O +AlCl4 turns into acylium ion
- Benzene + R-group becomes R-C=O + R+
Friedel-Crafts Alkylation
- R-Cl+ AlCl3; R-Cl is made to break RX bond resulting into R+ + AlCl4
- Benzene reacts with R+ which forms R
- Adding H forms an alkyl group through deprotonation
Disadvantages of Alkylation
- Polyalkylation
- Inability to produce a mono group easily
- CH3Cl+ AlCl3 becomes CH3
- +3HCl
Rearrangement
- CH3-CH2-CH2Cl + AlCl3 becomes CH3-CH2-CH2+AlCl3 becomes n-propyl benzene versus isopropyl benzene
- Hydride shift causes the 2° cation to become more stable
EWD (NO2, SO3H, COOH, CHO)
- CH3Cl/AlCl3: No reaction; a rich ring is needed
Strong ED (NH2, OH)
- NH2 Alcl3 creates complex that does not undergo F.C
Advantages of acylation
- No polyalkylation
- No rearrangement
- Used to obtain monoalkyl benzene by Clemmenson reduction (Zn/Hg/HCl) + ✈︎
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
