Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Preparation from Alcohols: Alcohols react with halogen acids (), phosphorus halides (, ), or thionyl chloride () to form haloalkanes. Thionyl chloride is preferred because the byproducts and are gases and escape easily.
Free Radical Halogenation: Alkanes react with or in the presence of UV light or heat. This usually results in a complex mixture of mono-, di-, and polyhaloalkanes.
Electrophilic Substitution: Haloarenes are prepared by the halogenation of aromatic hydrocarbons in the presence of Lewis acid catalysts like or in the dark.
Addition to Alkenes: Hydrohalic acids () add to alkenes. Symmetrical alkenes give one product, while unsymmetrical alkenes follow Markovnikov's Rule (the halogen attaches to the carbon with fewer hydrogen atoms).
Anti-Markovnikov Addition (Peroxide Effect): In the presence of organic peroxides, the addition of (not or ) to unsymmetrical alkenes occurs contrary to Markovnikov's rule.
Finkelstein Reaction: Used specifically for preparing iodoalkanes by reacting alkyl chlorides/bromides with in dry acetone.
Swarts Reaction: Used for preparing fluoroalkanes by heating alkyl chlorides/bromides in the presence of metallic fluorides like , , or .
Sandmeyer Reaction: Primary aromatic amines react with at to form diazonium salts, which then react with or to form haloarenes.
📐Formulae
💡Examples
Problem 1:
Identify the major product formed when Prop-1-ene reacts with in the absence of peroxide.
Solution:
The product is -Bromopropane.
Explanation:
According to Markovnikov's Rule, the negative part of the addendum () attaches to the doubly bonded carbon atom carrying the lesser number of hydrogen atoms. Thus, .
Problem 2:
Write the chemical equation for the preparation of Chloroethane from Ethanol using .
Solution:
Explanation:
Alcohols react with Phosphorus pentachloride to yield alkyl chlorides, phosphorus oxychloride, and hydrogen chloride.
Problem 3:
How is Iodobenzene prepared from Benzenediazonium chloride?
Solution:
Explanation:
Unlike chloro and bromoarenes, iodobenzene is prepared simply by shaking the diazonium salt solution with potassium iodide (); it does not require cuprous halides.