Chemical Reactions
Chapter Name : Haloalkanes And Haloarenes |
Sub Topic Code : 102_12_10_06_03 |
Topic Name : Chemical Reactions |
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Sub Topic Name : Elimination Reactions |
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Introduction
• When a haloalkane with b-hydrogen atom is heated with alcoholic solution of potassium hydroxide, there is elimination of hydrogen atom from b-carbon and a halogen atom from the a-carbon atom. • As a result, an alkene is formed as a product. Since b-hydrogen atom is involved in elimination, it is often called b-elimination. • If there is possibility of formation of more than one alkene due to the availability of more than one b-hydrogen atoms, usually one alkene is formed as the major product. • This was first observed by Russian chemist, Alexander Zaitsev (also pronounced as Saytzeff) who in 1875 formulated a rule which says that “in dehydrohalogenation reactions, the preferred product is that alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms.”
Pre-Requisites:
Elements, bond, halides
Activity:
• Synthetic halogen compounds, viz. • chloroquine is used for the treatment of malaria; • Halothane is used as an anaesthetic during surgery.
Real Life Question:
What are haloarenes and haloalkanes?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| - Haloalkanes - Haloarenes | • Haloalkanes contain halogen atom(s) attached to the sp3 hybridised carbon atom of an alkyl group. • Haloarenes contain halogen atom(s) attached to sp2 hybridised carbon atom(s) of an aryl group. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| • Chlorine containing antibiotic, chloramphenicol, produced by soil microorganisms is very effective for the treatment of typhoid fever. |
Real life uses :
• Synthetic halogen compounds, viz. ? chloroquine is used for the treatment of malaria; ? Halothane is used as an anesthetic during surgery..
Places to visit :
Pharmacy.
Practical examples around us
| Examples | Explainations |
|---|---|
| • Synthetic halogen compounds, viz. ? chloroquine is used for the treatment of malaria; ? Halothane is used as an anesthetic during surgery. |
What you learn in Theory:
• When a haloalkane with b-hydrogen atom is heated with alcoholic solution of potassium hydroxide, there is elimination of hydrogen atom from b-carbon and a halogen atom from the a-carbon atom. • As a result, an alkene is formed as a product. Since b-hydrogen atom is involved in elimination, it is often called b-elimination. • If there is possibility of formation of more than one alkene due to the availability of more than one b-hydrogen atoms, usually one alkene is formed as the major product. • This was first observed by Russian chemist, Alexander Zaitsev (also pronounced as Saytzeff) who in 1875 formulated a rule which says that “in dehydrohalogenation reactions, the preferred product is that alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms.”
What you learn in Practice:
• Haloalkanes and Haloarenes are classified based on the number of halogen compounds contained in them,