Organic Chemistry: Properties of Pyridine
48 Questions
0 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 type of reaction is Bonnemann cyclization classified as?

  • Electrophilic substitution
  • Cycloaddition reaction
  • Nucleophilic substitution
  • Diels-Alder reaction (correct)

    • What is the temperature required for the Diels-Alder reaction in the given reaction?

  • 300°C (correct)
  • 350°C
  • 200°C
  • 250°C

    • What is the pKa of pyridine?

  • 7.75
  • 8.25
  • 8.75 (correct)
  • 9.25

    • What type of reactions does pyridine undergo due to its electronic structure?

    <p>Electrophilic and nucleophilic substitution</p> Signup and view all the answers

    What is the nature of pyridine?

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

    What happens when pyridine reacts with strong acids?

    <p>It reacts to form salts</p> Signup and view all the answers

    What is the name of the reaction that involves the reaction of 1,3-butadiene?

    <p>Diels-Alder reaction</p> Signup and view all the answers

    What is the role of pyridine in some reactions?

    <p>Base or nucleophile</p> Signup and view all the answers

    What is the most common example of heterocyclic compounds?

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

    What is the hybridization state of the carbon atoms and nitrogen atom in pyridine?

    <p>sp2</p> Signup and view all the answers

    What is the orientation of the lone pair of electrons of the nitrogen atom in pyridine?

    <p>In the plane of the ring</p> Signup and view all the answers

    What is the condition for a compound to be aromatic, according to Huckel's rule?

    <p>(4n+2) π-electrons</p> Signup and view all the answers

    Why is pyridine basic?

    <p>Because of the availability of the nitrogen's lone pair to react with protons</p> Signup and view all the answers

    How can pyridine be represented?

    <p>As a resonance hybrid of several structures</p> Signup and view all the answers

    What determines the rate of the overall reaction in electrophilic and nucleophilic substitution?

    <p>The rate of the first step, formation of a charged particle</p> Signup and view all the answers

    What is the charge of the intermediate in electrophilic substitution?

    <p>Positively charged</p> Signup and view all the answers

    Why are the carbanions more stable in nucleophilic attack on a pyridine derivative compared to a benzene derivative?

    <p>Due to electron withdrawal by the nitrogen atom</p> Signup and view all the answers

    What is the effect of the nitrogen atom on the carbanions in nucleophilic attack?

    <p>It stabilizes the carbanions</p> Signup and view all the answers

    What is the hybrid of structures resulting from nucleophilic attack at the 4-position?

    <p>I, II, and III</p> Signup and view all the answers

    Why is the rate of the reaction affected by the ability of the ring to accommodate the charge?

    <p>Because it affects the stability of the intermediate</p> Signup and view all the answers

    What is the charge of the intermediate in nucleophilic substitution?

    <p>Negatively charged</p> Signup and view all the answers

    What is the effect of nucleophilic attack at the 2-position compared to the 4-position?

    <p>It resembles attack at the 4-position</p> Signup and view all the answers

    What is the other name of the compound shown in the figure?

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

    What is responsible for the basicity of Piperidine?

    <p>Unshared pair of electrons</p> Signup and view all the answers

    How would you classify Pyridine?

    <p>Aromatic compound</p> Signup and view all the answers

    What type of reactions is Pyridine nucleus highly deactivated towards?

    <p>Electrophilic substitution reactions</p> Signup and view all the answers

    What is the Kb value of Piperidine?

    <p>2 x 10^(-5)</p> Signup and view all the answers

    What is the name of the compound with a cyclic structure shown in the figure?

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

    What is the characteristic of Pyridine towards electrophilic substitution reactions?

    <p>Highly deactivated</p> Signup and view all the answers

    What is the name of the compound with an unsaturated ring shown in the figure?

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

    Why is structure Il especially stable?

    <p>Because the negative charge is located on the atom that can best accommodate it, the electronegative nitrogen atom</p> Signup and view all the answers

    What is the reason for pyridine being highly reactive towards nucleophilic substitution?

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

    What is the result of the reaction of pyridine with potassium hydroxide?

    <p>Formation of a keto-enol tautomerism</p> Signup and view all the answers

    What is the reactivity of pyridine towards electrophilic substitution?

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

    What is the nature of pyridine as a nucleophile?

    <p>As a tertiary amine, pyridine has nucleophilic properties</p> Signup and view all the answers

    What is the product of the reaction of pyridine with butyllithium?

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

    What is the role of the nitrogen atom in pyridine?

    <p>To decrease the reactivity of pyridine towards electrophiles</p> Signup and view all the answers

    What is the result of the reaction of pyridine with sodium amide?

    <p>Formation of a sodium salt</p> Signup and view all the answers

    Attack at the 3-position in pyridine is especially slow.

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

    Nitrogen in pyridine shares electrons readily and resists the removal of electrons.

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

    A structure in which nitrogen bears a positive charge is especially stable in pyridine.

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

    Substitution in pyrrole occurs predominantly at the 4-position.

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

    Pyridine is more reactive towards nucleophilic substitution than pyrrole.

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

    In pyrrole, nitrogen accommodates the positive charge by sharing three pairs of electrons.

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

    Attack at the 4-position is less favored in pyridine.

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

    Pyrrole is less reactive towards electrophilic substitution due to its electronic structure.

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

    The nitrogen atom in pyridine has an octet of electrons.

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

    Substitution in pyridine occurs predominantly at the 2-position or 4-position.

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

    Study Notes

    Structure and Properties of Pyridine

    • Pyridine is a planar molecule, similar to benzene, due to sp2-hybridized carbon and nitrogen atoms.
    • The lone pair of electrons on the nitrogen atom lies in the plane of the ring.
    • Pyridine is an aromatic compound, following the Huckel rule of aromaticity (4n+2 π-electrons).
    • The nitrogen's lone pair of electrons is in an sp2 orbital, perpendicular to the p orbitals of the ring, making it basic.

    Synthesis of Pyridine

    • Pyridine can be represented as a resonance hybrid of several structures.
    • It can be synthesized through Bonnemann cyclization and Diels-Alder reaction.

    Reactions of Pyridine

    • Pyridine undergoes electrophilic and nucleophilic substitution reactions typical of aromatic rings.
    • Pyridine acts as a base or nucleophile, with reactions involving the nitrogen atom directly.

    Basic Character of Pyridine

    • Pyridine is basic in nature, with a pKa of 8.75.
    • It reacts with strong acids to form salts and is also known as piperidine.

    Electrophilic Substitution Reactions

    • Pyridine is less aromatic than benzene and pyrrole, making it a highly deactivated aromatic nucleus towards electrophilic substitution reactions.
    • The reaction proceeds in two steps, with the rate of the first step determining the overall reaction rate.

    Nucleophilic Substitution Reactions

    • Nucleophilic attack at the 4-position yields a carbanion that is a hybrid of structures, which is especially stable due to the negative charge on the nitrogen atom.
    • Attack at the 3-position yields a carbanion that is also a hybrid of structures.
    • Pyridine is more reactive towards nucleophilic substitution than benzene, and more reactive at the 2- and 4-positions than at the 3-position.

    Other Reactions of Pyridine

    • Reaction with potassium hydroxide yields 2-hydroxypyridine through keto-enol tautomerism.
    • Reaction with organometallic compounds, such as butyllithium, yields 2-butylpyridine.
    • Reaction with sodium amide yields pyridinium chloride.

    Pyridine as a Nucleophile

    • As a tertiary amine, pyridine has nucleophilic properties, reacting with electrophiles to form products such as pyridinium chloride.

    Pyridine Synthesis

    • Hantzsch Synthesis: condensation of beta-dicarbonyl compound, ammonia, and aldehyde leads to 1,4-dihydropyridine derivative, which on oxidation with HNO3 yields pyridine derivative.
    • From Pyrrole: Pyrrole heated with methylene chloride in presence of sodium ethoxide forms pyridine.
    • From Picoline: Beta-picoline on oxidation with potassium dichromate and sulfuric acid gives nicotinic acid, which on decarboxylation with calcium oxide gives pyridine.

    Electrophilic Substitution in Pyridine

    • Pyridine is less reactive towards electrophilic substitution reactions due to:
      • Higher electronegativity of nitrogen atom reduces electron density on nitrogen atom.
      • Pyridine forms pyridinium cation with electrophile, decreasing electron density on nitrogen atom.
    • Substitution reactions occur mainly at the 3-position (or β-position) due to the stability of the resulting intermediate.

    Comparison with Pyrrole

    • In pyrrole, nitrogen bears a positive charge, which is a stable state due to every atom having an octet of electrons.
    • In pyridine, nitrogen bearing a positive charge is unstable due to nitrogen having only a sextet of electrons.

    Reactivity of Pyridine

    • Pyridine undergoes nitration, sulfonation, and halogenation only under vigorous conditions.
    • Pyridine does not undergo Friedel-Crafts reaction.

    Studying That Suits You

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

    Quiz Team

    Related Documents

    Organic Chemistry 3, Lecture 4, Dr. Yusuf (PDF)

    Description

    This quiz covers the properties of pyridine, a heterocyclic compound, including its planar molecular structure and aromaticity. It also discusses the hybridization of carbon and nitrogen atoms and the arrangement of electrons.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser