Heterocyclic Ring Reactions
40 Questions
1 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the product of the reaction of pyrrole with CHCl3 and strong alkali?

  • Formylation at position 3
  • Formation of 2-chloro pyrrole
  • Formylation at position 2 and formation of 3-chloro pyridine (correct)
  • Formation of amines

    • What is the product of the reaction of pyrrole with aldehydes and ketones in acidic medium?

  • Porphyrin
  • Dipyrryl methane (correct)
  • Dipyrryl ethane
  • Tetramer

    • What is the order of reactivity in five-membered heterocycles?

  • Thiophene > Pyrrole > Furan > Benzene
  • Pyrrole > Thiophene > Furan > Benzene
  • Furan > Thiophene > Pyrrole > Benzene
  • Pyrrole > Furan > Thiophene > Benzene (correct)

    • What is the name of the reaction that forms a 3-chloro pyridine from pyrrole?

    <p>Riemer Tiemann Reaction</p> Signup and view all the answers

    What is the name of the reaction that forms amines from pyrrole?

    <p>Hoffmann Martius Rearrangement</p> Signup and view all the answers

    What is the structure of the tetramer formed by the reaction of pyrrole with aldehydes and ketones?

    <p>A planar, stable structure that can accommodate a wide range of metal ions</p> Signup and view all the answers

    What is the condition required for the reaction of pyrrole with aldehydes and ketones?

    <p>Acidic medium</p> Signup and view all the answers

    Which heterocycle is the most aromatic?

    <p>Benzene</p> Signup and view all the answers

    Why is pyrrole more reactive towards electrophiles?

    <p>Due to the electron releasing ability of trivalent nitrogen</p> Signup and view all the answers

    Why is furan less reactive than pyrrole towards electrophiles?

    <p>Due to the electronegative nature of oxygen</p> Signup and view all the answers

    Why is thiophene less reactive than furan towards electrophiles?

    <p>Due to the less effective overlapping of p-orbitals of carbon and sulfur</p> Signup and view all the answers

    What is the order of reactivity of heterocycles towards electrophiles?

    <p>Pyrrole &gt; Furan &gt; Thiophene</p> Signup and view all the answers

    What is the position of nitration in furan when reacted with a mild nitrating agent?

    <p>C-2</p> Signup and view all the answers

    What is the preferred site of electrophilic attack on furan?

    <p>C-2</p> Signup and view all the answers

    What is the reason for the lower reactivity of benzene towards electrophiles?

    <p>Greater resonance stabilisation energy</p> Signup and view all the answers

    What is the order of stability of the transition states in heterocyclic ring reactions?

    <p>Furan &gt; Thiophene &gt; Benzene</p> Signup and view all the answers

    What is the reason for the lower reactivity of phenol compared to aniline?

    <p>Due to the electronegative nature of oxygen</p> Signup and view all the answers

    Why does furan tend to give addition products rather than substitution products?

    <p>Due to the possibility of forming stable bonds like C-O bonds</p> Signup and view all the answers

    What is the main factor that determines the reactivity of heterocycles towards electrophiles?

    <p>All of the above</p> Signup and view all the answers

    What is the relative reactivity of thiophene and furan towards electrophiles?

    <p>Furan is more reactive than thiophene</p> Signup and view all the answers

    Why is electrophilic substitution in thiophene much easier than in benzene?

    <p>Due to the lower resonance stabilisation energy of thiophene</p> Signup and view all the answers

    Which of the following compounds is the most aromatic?

    <p>Benzene</p> Signup and view all the answers

    What is the correct order of reactivity in electrophilic substitution in comparison to benzene?

    <p>Pyrrole &gt; Furan &gt; Thiophene &gt; Benzene</p> Signup and view all the answers

    Which positions are more reactive in pyrrole?

    <p>2 &amp; 5 positions</p> Signup and view all the answers

    Why does the intermediate from electrophilic attack at C2 in pyrrole have more resonance structures?

    <p>Due to the ability of the nitrogen atom to donate electrons</p> Signup and view all the answers

    Which of the following compounds does not undergo Friedel-Crafts alkylation?

    <p>Furan</p> Signup and view all the answers

    What is the reason for the acid sensitivity of furan in Friedel-Crafts alkylation?

    <p>Due to the formation of polymers</p> Signup and view all the answers

    What is the condition required for Friedel-Crafts alkylation of furan substituted with electron-withdrawing substituents at the position-2?

    <p>Room temperature</p> Signup and view all the answers

    What is the role of mild catalysts such as phosphoric acid or boron trifluoride in Friedel-Crafts alkylation of furan?

    <p>They facilitate alkylation at the position-2</p> Signup and view all the answers

    What is the major difference between the reactivity of pyrrole and benzene in electrophilic substitution reactions?

    <p>Pyrrole is more reactive due to the presence of a nitrogen atom</p> Signup and view all the answers

    What is the primary reason for the difference in reactivity between the 2 and 3 positions in pyrrole?

    <p>The difference in the number of resonance structures that can stabilize the intermediate</p> Signup and view all the answers

    Which of the following heterocycles is least reactive towards electrophiles?

    <p>Benzene</p> Signup and view all the answers

    What is the role of electron-withdrawing substituents in the Friedel-Crafts alkylation of furan?

    <p>They allow furan to undergo Friedel-Crafts alkylation at room temperature</p> Signup and view all the answers

    Why does furan not undergo Friedel-Crafts alkylation under normal conditions?

    <p>Due to the acid sensitivity of furan</p> Signup and view all the answers

    What is the relative order of aromaticity of the five-membered heterocycles?

    <p>Benzene &gt; Thiophene &gt; Furan &gt; Pyrrole</p> Signup and view all the answers

    What is the primary reason for the difference in reactivity between pyrrole and furan towards electrophiles?

    <p>The difference in the number of resonance structures that can stabilize the intermediate</p> Signup and view all the answers

    What is the role of mild catalysts in the Friedel-Crafts alkylation of furan?

    <p>They allow furan to undergo Friedel-Crafts alkylation at room temperature</p> Signup and view all the answers

    Why is pyrrole more reactive than benzene towards electrophiles?

    <p>Due to the electron-donating nature of the nitrogen atom</p> Signup and view all the answers

    What is the relative order of reactivity of the five-membered heterocycles towards electrophiles?

    <p>Pyrrole &gt; Furan &gt; Thiophene &gt; Benzene</p> Signup and view all the answers

    What is the primary reason for the difference in reactivity between the 2 and 5 positions in pyrrole?

    <p>The difference in the number of resonance structures that can stabilize the intermediate</p> Signup and view all the answers

    Study Notes

    Heterocyclic Ring Reactions Overview

    • Heterocyclic compounds resemble phenols in several reactions.
    • Key reactions include the Riemer-Tiemann reaction and Kolbe-Schmitt reaction.

    Riemer-Tiemann Reaction

    • Involves pyrrole reacting with CHCl3 and strong alkali.
    • Produces formylation at position 2 or formation of 3-chloro pyridine.
    • Generates carbine, leading to a carbine insertion reaction.

    Reaction of Pyrrole with Aldehydes and Ketones

    • Pyrrole condenses with aldehydes/ketones in acidic medium.
    • Initially forms dipyrryl methane, which can polymerize to tetramers (porphyrinogens).
    • Porphyrinogens are stable, planar structures that accommodate metal ions.

    Reactivity Comparison of Five-Membered Heterocycles

    • Reactivity order: Pyrrole > Furan > Thiophene > Benzene.
    • Aromaticity order: Benzene > Thiophene > Furan > Pyrrole.
    • Pyrrole's greater reactivity is due to electron-rich carbon atoms and stabilization of positive charge on tetravalent nitrogen.

    Furan Reactivity

    • Furan is reactive but less than pyrrole, primarily at C-2.
    • Oxygen's electronegativity results in less stability of the positive transition state compared to nitrogen in pyrrole.

    Thiophene Reactivity

    • Thiophene is less reactive than furan, attributed to sulfur’s lower electronegativity.
    • The mesomeric effect of sulfur is smaller than that of oxygen, leading to weaker electron release from the aromatic system.

    Benzene vs. Heterocycles Reactivity

    • Electrophilic substitution in thiophene is easier than in benzene.
    • Benzene shows lower reactivity due to higher resonance stabilization energy and transition state energy.
    • Benzene's transition state stability is lower compared to five-membered heterocycles.

    Aromaticity and Substitution vs. Addition

    • Furan's lower aromaticity can lead to preferential formation of stable C-O bonds over substitution products.
    • Aromaticity decrease generally favors addition reactions over substitution reactions.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Organic Chemistry - Heterocyclic Compounds - Ring Reactions PDF

    Description

    Test your knowledge of heterocyclic ring reactions, focusing on pyrrole and its reactions with aldehydes and ketones, as well as its resemblance to phenol. Learn about the Riemer Tiemann reaction and more. Assess your understanding of pyrrole's reactivity and comparison with benzene.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser