Unsaturated compounds 2024
Unsaturated Compounds
By: Dr. Zahra Kassem
Page 1: Overview of Alkenes
Objectives:
Understand naming methods for organic compounds.
Provide both IUPAC and common names for Alkenes.
Recognize important methods for Alkenes synthesis.
Learn about different reactions of Alkenes:
Hydrogenation (Reduction)
Electrophilic Addition (includes Markovnikov’s & Anti-Markovnikov’s rules)
Oxidation of Alkenes
Page 2: Alkynes and Dienes
Objectives:
Understand naming methods for organic compounds.
Provide both IUPAC and common names for Alkynes.
Recognize important methods for Alkynes synthesis.
Learn about reactions of Alkynes and Conjugated Dienes.
Classification of Unsaturated Compounds:
Alkenes
Alkynes
Conjugated Dienes
Page 3: Nomenclature of Alkenes
IUPAC Nomenclature:
Replace the –ane suffix with –ene.
Determine the parent name by identifying the longest chain containing the double bond.
Assign numbers to give the double bond the lowest number possible.
Indicate substituent location by the carbon numbers they are attached to.
Page 4: Multiple Double Bonds
For compounds with multiple double bonds:
Indicate each double bond's location using the same numbering principle.
Use di- for two double bonds, tri- for three before the -ene suffix.
Examples:
CH₂=CH-CH₂-CH=CH₂: 1,4-pentadiene
CH₂=CH-CH=CH₂: 1,3-butadiene
Page 5: Preparation of Alkenes
Action of concentrated sulfuric acid on primary alcohols at 160-170°C (dehydration).
Action of ethanolic potassium hydroxide on mono-halo derivatives.
Zinc dust on methanolic solutions of dihalogen derivatives.
Page 6: Chemical Reactions of Alkenes
I. Hydrogenation: Addition of H₂ to Alkenes.
II. Electrophilic Addition:
Addition of electrophilic reagents (HX) to the double bond forming carbocations.
Page 7: Markovnikov’s Rule
Markovnikov’s Rule:In HX addition to alkene, H+ adds to the carbon with more hydrogen atoms.
Example question: Product of Markovnikov’s addition of HCl to propene.
Page 8: Anti-Markovnikov Addition
Radical Addition:
Addition of hydrogen halide in presence of peroxide (Free Radical Condition).
Addition of Halogens:
Cl₂/CCl₄ or Br₂/CCl₄ under free radical or ionic conditions.
Test for Alkene:
Reddish-brown color of Br₂ disappears upon addition to alkene.
Page 9: Hydration of Alkenes
Mechanism:Acid-catalyzed hydration follows Markovnikov’s Rule; the acid is not consumed during the reaction.
Page 10: Oxidation of Alkenes
Oxidation with KMnO₄:
Purple color disappears, distinguishes between alkanes and alkenes; Syn-addition of hydroxyl groups.
Alkynes (Acetylenes):
M.F.= CnH2n-2, simplest member is acetylene.
Named similarly to alkenes with suffix –yne for triple bonds.
Page 11: Preparation of Alkynes
Action of ethanolic KOH on ethylene bromide (vicinal dihalide).
Page 12: More Preparations
KOH/EtOH on ethylidene chloride (geminal dihalide).
Sodamide in liquid ammonia.
Page 13: Acidity of Terminal Alkynes
Acetylene and terminal alkynes form metal derivatives with silver and copper (used to differentiate terminal vs. non-terminal alkynes).
Page 14: Reactions of Alkynes
Addition of H₂/Pt
Addition of Cl₂ or Br₂
Addition of HBr or HCl
Page 15: Conjugated Dienes
Dienes have more than one double bond:
Dieness (two), Trienes (three), Tetraenes (four).
Conjugation: Alternating double and single bonds.
Page 16: Reactions of Conjugated Dienes
1,2- vs. 1,4- Addition:
Reactions yield both products, depending on reaction temperature.
Lower temperatures favor 1,2-addition (kinetic control).
Higher temperatures favor 1,4-addition (thermodynamic control).
Page 17: Diels-Alder Reaction
A type of 1,2-addition involving cyclic transition state to yield products.
Promoted by electron-withdrawing substituents in dienophile.
Page 18: References
Textbooks by Wilson and Gisvold, T. W. Graham Solomons, and others provide comprehensive background on Organic Chemistry.