Organic Chemistry Chapter 5: Addition Reactions
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Questions and Answers

What type of derivative is produced when alkenes react with halogens?

  • 1,2-dihalogen derivatives (correct)
  • Alkyl halides
  • Trihalogen derivatives
  • Monohalogen derivatives

What occurs first in the mechanism of halogenation of alkenes?

  • Departure of the further halogen as a halide
  • Flow of electrons from the Ï€ bond to the nearer halogen (correct)
  • Formation of ring intermediates
  • Formation of alkenyl halides

Which of the following halogens readily reacts with alkenes?

  • Chlorine (Cl2) (correct)
  • Argon (Ar)
  • Fluorine (F2)
  • Iodine (I2)

What role does the farther halogen play during the reaction mechanism?

<p>It departs as a halide nucleophile (A)</p> Signup and view all the answers

Which step correctly follows after the reactants get closer in the halogenation mechanism?

<p>Departure of the further halogen (D)</p> Signup and view all the answers

What defines an addition reaction?

<p>All reagent atoms are added to the reactant, resulting in a product that contains all atoms from both. (B)</p> Signup and view all the answers

Which type of addition reaction involves electron pair donation for bond formation?

<p>Both A and B (D)</p> Signup and view all the answers

Which of the following compounds is most likely to undergo addition reactions?

<p>Alkenes (B)</p> Signup and view all the answers

What type of addition reaction occurs at a conjugated system?

<p>Both B and C (A)</p> Signup and view all the answers

What is a unique characteristic of rearrangement reactions?

<p>They involve the reorganization of existing bonds and atoms within a molecule. (C)</p> Signup and view all the answers

Flashcards

Addition Reaction

A chemical reaction where all atoms of the reagent are added directly to the reactant, forming a new molecule that contains all atoms from both the reactant and reagent.

Addition Reaction: Unsaturated Compounds

Reactions where the reagent adds to a carbon-carbon double or triple bond in an unsaturated molecule.

Electrophilic Addition

A type of addition reaction where an electron-seeking species (electrophile) attacks a site of high electron density, often a double or triple bond.

Nucleophilic Addition

A type of addition reaction where a nucleophile, a species with an electron pair, attacks a site of low electron density, often a carbocation.

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Nucleophilic Addition at Conjugated System

A type of addition reaction where a nucleophile attacks a conjugated system, a system of alternating double and single bonds.

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Halogenation of Alkenes

A chemical reaction where a halogen molecule (like Cl2 or Br2) adds across a carbon-carbon double bond in an alkene to form a dihaloalkane.

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Rate Law for Halogenation

The rate of a halogenation reaction is directly proportional to the concentrations of both the alkene and the halogen.

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Halogenation Mechanism

The mechanism of halogenation involves a two-step process. In the first step, the π electrons of the alkene attack one of the halogen atoms, forming a cyclic halonium ion intermediate. In the second step, the halide ion attacks the halonium ion to form the dihaloalkane.

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Halonium Ion

The halonium ion is a three-membered ring intermediate that is formed during the halogenation reaction.

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Electrophile

It is a species that seeks out electrons. In halogenation, it is the halogen molecule (Cl2, Br2) that acts as the electrophile because it is attracted to the electron-rich double bond of the alkene.

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Study Notes

Lecture 5: Addition Reactions and Their Mechanisms

  • Addition reactions involve adding all reagent atoms to the reactant, resulting in a product containing all original and added atoms.
  • Unsaturated compounds (alkenes and alkynes) feature double or triple bonds, which act as electron-pair donors for bond formation in these reactions.
  • Different types of addition reactions exist: electrophilic addition, nucleophilic addition, nucleophilic addition to conjugated systems, and free radical addition.

Types of Addition Reactions

  • Electrophilic Addition: A characteristic reaction of alkenes where pi electrons react with electrophiles.

    • Electrophiles include proton donors (Brønsted-Lowry acids), neutral reagents (like bromine), and Lewis acids (like BH3, BF3, AlCl3).
    • Carbocation formation is the rate-determining step.
    • Rate = k[alkene][ENu]
    • Halogen addition (halogenation) is a type of electrophilic addition involving halogens like chlorine (Cl2) and bromine (Br2). This leads to 1,2-dihalogen derivatives. The mechanism involves Ï€-electron polarization of the halogen, electrophilic addition, and bromide attack on the carbocation.
    • Addition of bromine to an alkene results in a racemic mixture (R,R and S,S isomers) in the addition to cis-alkene, while it forms a meso isomer (R,S isomer) in the addition to trans-alkene. The addition is anti-addition, which places the halogen atoms on opposite faces of the double bond.
    • Electrophilic addition of hydrogen halides (HX) to alkenes (hydrohalogenation) follows Markovnikov's rule. The hydrogen atom adds to the carbon atom with the most hydrogen atoms. The result is a pair of enantiomers, while the resulting addition to symmetric alkenes forms a single product.

  • Nucleophilic Addition:

    • The nucleophile attacks a carbon atom, forming a carbanion intermediate.

  • Nucleophilic Addition to Conjugated Systems: Conjugate addition (or 1,4-addition) occurs when a nucleophile adds to a conjugated system (e.g., a conjugated diene).

  • Free Radical Addition: Free radical addition occurs when peroxides are present, producing an anti-Markovnikov product; with this process, the hydrogen attaches to the carbon atom with fewer hydrogen atoms. The addition of HBr to a conjugated diene proceeds with 1,2-addition and 1,4-addition.

Rearrangement Reactions

  • Rearrangement reactions involve a change in the carbon skeleton of a molecule forming a structural isomer of the original molecule. A substituent in the molecule moves from one atom to another atom. Migrating groups don't leave the molecule.
  • Classification includes those to electron-deficient carbon (Wagner-Meerwein, Pinacol, Benzilic Acid, Arndt-Eistert) and those to electron-deficient nitrogen (Hofmann, Curtius, Schmidt, Lossen, Beckmann).

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Addition Reactions and Their Mechanism Lecture Notes PDF

Description

Explore the mechanisms of addition reactions in unsaturated compounds such as alkenes and alkynes. This quiz covers various types of addition reactions, including electrophilic and nucleophilic additions, and the role of electron-pair donors in bond formation.

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