1. Alkenes
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2. Alkenes Ethene (ethylene) C2H4 C3H6 Propene C4H8 Butene C5H10 Pentene
Name
Alkenes
Molecular formula
Ethene (ethylene)
Propene
Butene
Pentene
C2H4
C3H6
C4H8
C5H10
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3. Alkenes are also called olefins.
Alkenes contain a carbon—carbon double bond.
Terminal alkenes have the double bond at the end of the carbon chain
Internal alkenes have at least one carbon atom bonded to each end of the double bond.
Cycloalkenes contain a double bond in a ring.
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5. The double bond consists of a  bond and a  bond.
Each carbon is sp2 hybridized and trigonal planar, with bond angles of approximately 120°.
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6. Terpenes
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10. Terpenes
Any of a large group of volatile unsaturated hydrocarbons found in the essential oils of plants, especially conifers and citrus trees. They are based on a cyclic molecule having the formula C10H16.
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11. Alkenes and alkene derivatives are responsible for the odor of many plants
Structure is based on a five-carbon diene called Isoprene (2-methyl-1,3-butadiene)
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12. The isoprene structural unit is encountered in Terpenes in several variant forms that differ in location and in number of double bonds
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13. The number of carbon atoms present on a Terpene is always a multiple of the number 5(10.15,20…….)
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14. β-carotene Responsible for yellow color of carrots
Structure is 40 carbon atoms
Many isoprene 8 isoprene unit
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15. Beta-carotene serves as a precursor for vitamin A
Splitting of beta carotene molecule produces two vitamin A molecules
It also function as an antioxidant
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16. Two isoprene unit
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17. α -Phellandrene
( eucalptus)
Myrcene
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18. Geranoil
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19. α- Farnesene (natural apple coating)
Zingiberene (ginger)
α- Farnesene (natural apple coating)
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20. Menthol
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21. Physical properties Insoluble in water Soluble in non polar solvent
Physical properties similar to alkanes
Alkenes with 1-4 carbon atoms are gases at room temperature
5-17 carbon atoms are liquids at room temperature
Above 17-all are solids
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22. Chemical Properties of Alkenes
Addition Reactions
Combustion Reactions
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23. Addition Reactions Why do alkenes undergo addition reactions?
Carbon-carbon double bonds in alkenes are reactive.
readily undergoes addition reactions
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24. Unsaturated hydrocarbon
Addition Reactions +
Unsaturated hydrocarbon
Saturated organic
compound
In an addition reaction, carbon-carbon double bonds become single bonds. This means that an unsaturated hydrocarbon becomes a saturated organic compound.
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25. Types of Addition Reactions
General Equation:
Reaction with ethene
Reaction Conditions
Equation (Write it yourself)
Bromination
(Addition of bromine) -
Hydrogenation
(Addition of hydrogen)
200 °C, nickel catalyst
Hydration
(Addition of steam)
phosphoric(V) acid catalyst, °C, 60 atm C H Br +
Br2 C H + H2 C H OH +
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26. Explanation
C-c double bond has σ-bond component and a π- bond component
The π- bond is weaker than the σ-bond and can be broken while the σ-bond remains intact
This happens in alkenes addition reactions
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27. Classification of addition reaction
Symmetrical addition
Unsymmetrical addition
Example:
Hydrogenation and Halogenation
Hydrohalogenation
Hydration
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28. Types of Addition Reactions
General Equation:
Reaction with ethene
Reaction Conditions
Equation (Write it yourself)
Bromination
(Addition of bromine) -
Hydrogenation
(Addition of hydrogen)
200 °C, nickel catalyst
Hydration
(Addition of steam)
phosphoric(V) acid catalyst, °C, 60 atm C H Br +
Br2 C H + H2 C H OH +
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29. Five addition reactions of cyclohexene
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30. Hydrogenation
Involves addition of a hydrogen atom to each carbon of the double bond
It is done by heating alkene and H2 in the presence of catalysis
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32. The identity of the catalyst used in the hydrogenation is specified by writing it above the arrow in the chemical equation
The hydrogenation of vegetable oils is very important commercial process today
Vegetable oils from sources as soyabeans and cottonseeds are composed of long chain organic molecules that contain double bonds
On hydrogenation these oils are converted to low-melting solids that are used in margarines
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33. Halogenation of alkenes
It involves the addition of a halogen atom to each carbon of the double bond
It involves chlorination and bromination
No catalysis is needed
Product is always a dihalogenated alkene derivative
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34. Bromine in water or CCl4 is reddish brown
Bromination often used to test for the presence of C=C double bonds in organic substances
Bromine in water or CCl4 is reddish brown
The dibromides formed from symmetrical addition of bromine to an organic compound are colorless
The decolrization of a bromine solution indicates the presence of C=C
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35. Unsymmetrical Additions Hydrohalogenation Hydration
Addition of HCl, HBr or HI to a C=C
No catalyst is required
Hydrohalogenation—Markovnikov’s Rule
With an unsymmetrical alkene, HX can add to the double bond to give two constitutional isomers, but only one is actually formed:
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36. The rule states that, with the addition of HX to an alkene, the hydrogen (H) becomes attached to the carbon with fewer alkyl substituents, and the halide (X) group becomes attached to the carbon with more alkyl substituents
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37. Transversely, the hydrogen atom is added to the carbon with the greater number of hydrogen atoms while the X component is added to the carbon with the least number of hydrogen atoms
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39. Markovnikov’s rule
States that in the addition of HX to an unsymmetrical alkene, the H atom adds to the less substituted carbon atom—that is, the carbon that has the greater number of H atoms to begin with.
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40. Halogenation—Addition of Halogen
Halogenation is the addition of X2 (X = Cl or Br) to an alkene to form a vicinal dihalide(“X” on adjacent Carbon)
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41. Example of Markovnikov’s Rule Hydration—Addition of H-OH
Hydration of 1-propene to form 2-propanol (major) and 1-propanol (minor)
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42. More than one C=C dienes, trienes
Addition occurs at every C=C bond but amount is as per double bonds
CH2 =CH-CH2-CH2-CH2CH3 + H CH3-(CH2)4-CH3
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43. Polymerization
A Polymerization reaction is a reaction in which the repetitious combining small molecules produces a very large molecule
The large unit is called Polymer
It’s a large molecule composed of many identical repeating units
The small repeating units are called Monomers
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44. Addition polymers
An addition polymer is a polymer in which the monomers simply “add together” with no other products formed besides the polymer
The monomers for addition polymers are most often alkenes or substituted alkenes
π- bond bonds present in the alkene monomers are broken
Electrons involved in π- bond make σ-bond with C-C between the monomers
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45. How are these formed The π- bonds of alkenes are broken
The electrons are now involved in carbon-carbon bonds between the monomers
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47. Applications Telecom Ducts Containers Folding tables and chairs
Chemical-resistant, heat-resistant pipes
The exact formula for a polymer cannot be written because the length of the carbon chain varies from polymer molecule to polymer molecule
Formula of polyethylene
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48. Addition Polymers
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