1. ALKENES

2. Unsaturated chemical compound containing at least one carbon-carbon double bond, where rotation about the C=C is very difficult.
To show the presence of the double bond, the –ane suffix from the alkane name is changed to –ene.
Also called olefins( fat dissolving)
sp2 atomic orbitals
Trigonal planar, 120o degree

3. Geometric Isomerism
Cis-trans isomerism
-isomers that have same order of atom attachment but a different arrangement of their atoms in space.

5. CnH2n where n is the number of carbon atoms in the molecule
General Formula
CnH2n
where n is the number of carbon atoms in the molecule

6. Physical Properties
Physical state -The first lower member like ethene, propene and butene are colorless gases.
 Density - lighter than water.  
Solubility - insoluble in water and soluble in nonpolar organic solvents.
more reactive than alkanes due to their double carbon-carbon bond.

7. Boiling point -The boiling points of alkenes gradually increase with an increase in the molecular mass.
 The cis isomer ( example cis-2-butene, b.p.= 3.7°C) is higher in bpt than its trans isomers (example, trans-2-butene, b.p.= 1°C) 

8. Melting point 
The melting points of alkenes increase with an increase in the molecular mass.

9. Natural Sources Isolated from petroleum.
Plant material like plant hormone, like Ethylene – a natural ripening agent and Terpenes – found in essential oil.

10. Some Common Alkene Polymers and their Uses
Ethylene H2C=CH2 Polyethene, Polythene Packaging, cable insulation, films and sheets
Tetrafluoroethene F2C=CF2 Polytetrafluoroethene, PTFE, Teflon Coatings, gaskets.
Chloroethene (vinyl chloride) H2C=CHCl Polyvinyl chloride, PVC, Tedlar Insulation, films, pipes
Styrene H2C=CHC6H5 Polystyrene, Styron Foam for packaging etc.
Vinyl acetate H2C=CHOCOCH3 poly(vinyl acetate), PVA
Paints, adhesives.

11. Preparations of Alkenes
1. Dehydrohalogenation of Alkyl halides
2. Dehydration of Alcohol
3. Dehalogenation of Vicinal Halides
4. Reduction of Alkynes

12. Preparations of alkenes
1. Dehydrohalogenation of alkyl halides
Preparations of alkenes
3° > 2° > 1°
Example:
n-butyl chloride 1-butene

13. Dehydrohalogenation of Alkyl Halides
Is an Elimination reaction. The term "elimination" describes the fact that a small molecule is lost during the process.
Different mechanisms are possible:
Loss of the LG to form a carbocation,  removal of H+ and formation of C=C bond
Simultaneous H+ removal, C=C bond formation and loss of the LG
Removal of H+ to form a carbanion, loss of the LG and formation of C=C bond.

14. 2. Dehydration of alcohol
3° > 2° > 1°
ex.

15. n-butyl alcohol 1-butene 2-butene
(chief product)
sec-butyl alcohol butene butene
(chief product)

16. Dehydration of Alcohols
It is the elimination of water molecule from alcohol to convert into alkene.
Lost of H and OH from adjacent carbons
An acid catalyst alkene.

17. Mechanism of Alcohol Dehydration
Step 1 : Alcohol unites with a hydrogen ion to form the protonated alcohol Step 2 : Alcohol associates into water and carbonium ion. Step 3 : The carbonium ion then loses a hydrogen ion to form alkene.

18. Dehalogenation of vicinal dihalides (same side)
Example:
2,3- Dibromobutane 2- butene

19. 4. Reduction of alkynes

20. Reduction of Alkynes Reducing Alkynes to form trans or cis Alkenes.
Using Na/ NH3
Step 1:
Sodium transfer an electron to the alkyne giving a radical anion.
Step 2: The radical anion removes a proton from the ammonia in an acid/base reaction

21. Step 3: A second atom of sodium transfers another electron to the alkyne giving an anion. Step 4 : the anion removes proton from the ammonia in an acid/base reaction.

22. Reactions of Alkene Halogenation Hydration Hydrogenation
Addition of hydrogen Halides
Addition of sulfuric acid
Addition of Carbenes
Addition of Free Radical

23. Allylic Hydrogenation
Dimerazation
Alkylation
Polymerization
Hydroxylation
Halohydrins formation
Ozonolysis
Hydroboration-oxidation
Epoxidation

24. Reactions of Alkenes
1. Addition of Halogens (X2)
Example.

25. Halogenations – Addition of Halogens
When an alkene is treated at room temperature with a solution of bromine or chlorine in carbon tetrachloride or some other inert solvent, the halogens adds rapidly to the double bond of the alkene to give the corresponding vicinal dihalide ( two halogens attached adjacent carbons

26. 2. Addition of Hydrogen (catalytic hydrogenation)
Ex.

27. Hydrogenation of Alkenes
The relationship between reactants and products in addition reactions can be illustrated by the hydrogenation of alkenes yield alkanes.Hydrogenation is the addition of H2 to a multiple bond.

28. 3. Addition of hydrogen halides

29. Ex.
The presence or absence of peroxide has no effect on the orientation of addition of HCl and HI, sulfuric acid and water.

30. Ex.

32. Addition of hydrogen halides
In the addition of an acid to the C=C of an alkene, the hydrogen of the acid attaches itself to the carbon that already holds the greater number of hydrogens
The reactivity of alkene, with halogen acids is in the order;.
HI > HBr > HCl

33. 4. Addition of sulfuric acid
Ex.

34. Follows Markovnikov addition

35. 5. Addition of water. HYDRATION

36. Ex.
FOLLOWS MARKOVNIKOV’S RULE

37. Addition of Water - Hydration
When heated with water in the presence of an acid catalyst, alkenes yield alcohol ROH.
The process is called hydration of alkenes because it involves the addition of water across the double bond.
The addition of the HOH across the double bonded carbon that bears the greater number of hydrogen atoms and the hydroxyl groups goes to the other double-bonded carbon

38. 6. Halohydrin formation
Ex.

39. Sterospecific:

40. 7. Dimerization (di = two, mer = part, product contains exactly twice
the # of C & H atom as the original).

41. Mechanism:
Addition of the tert-butyl cation to iso butylene; the orientation of addition is duch to yield the more stable tertiary cation. Step(2) brings about the union of two : isobutylene units, which is of course necessary for the product.

42. 8. Alkylation
ex.

43. mechanism: Addition of a hydrogen ion to form carbocation
Addition of a tert-butyl carbocation to isobutylene
Carbocation abstracts a hydrogen atom with its pair of electrons from a molecule of alkane. This abstraction of hydride ion yields an alkane of 8 carbons and a new carbocation to continue the chain.

44. A carbocation may:
a.) combine with a negative ion or other basic molecule
b.) rearrange to a more stable cabocation
c.) eliminate a hydrogen ion to form an alkene
d.) add to an alkene to form a larger carbocation
e.) abstract a hydride ion from an alkane

45. 9. Oxymercuration - demercuration
Oxymercuration – involves addition to the C=C of OH and HgOAc (mercuric ion)
Demercuration – the HgOAc is replaced by H

46. Ex. Follows Markovnikov addition
Undergo the process of oxymercuration, involves addition to the carbon – carbon double bond of –OH+ -HgOAc
Follows Markovnikov
addition
Mercury acetate in the presence of water to give hydroxy-mercurial compounds which on reduction yields alcohol. Oxymercuration involves addition to C=C of OH and –HgOAc is replaced by H. Sodium borohydride used to reduced the cmp to alcohol

47. 10. Hydroboration – oxidation
With the reagent Diborane, alkenes undergo hydroboration to yield alkylboranes, which on oxidation give alcohols.

48. Mechanism:
Hydroboration involves the addition of the double bond of BH3 w H becoming attach to one doubly bonded carbon and boron to the other. The alkylborane can then undergo oxidation in which the boron is replaced by –OH. Thus, the 2 – stage reaction process of hydroboration oxidation permits the effect. The addition to the carbon – carbon double bond of elements of H-OH.

50. 11. Addition of free radicals

51. Mechanism:

52. Electrophilic addition : Markonikov orientation

53. Free – radical Addition : Anti – Markovnikov orientation

54. 12. Polymerization of Alkenes
Polymerization – the joining together of many small molecules to form very large molecules.
Monomers – the simple compounds form which polymers are made.
Ex.
5 processes of polymerization
1. Free - radical polymerization
2. Cationic polymerization
3. Anionic polymerization
4. Condensation polymerization
5. Coordination polymerization

55. Free – radical polymerization
Polyvinyl chloride - use to make phonograph, records, plastic pipes, when plasticized with high boiling esters – raincoats, shower curtains and coatings for metal and upholstery fabrics.
Peroxide – initiator, required in small amount in polymerization
Free radical initiator
Mechanism:
Free radical adds to molecule of alkenes which for another free radical

56. This radical adds to another molecule of alkene to generate another free radical. This radical adds to another molecule of alkene to generate a still larger radical

57. 13. Addition of Carbenes. Cycloaddition
carbenes – derivative of methylene
Methylene is highly reactive

58. Methylene exist into 2 different forms
singlet methylene – unshared electrons are paired, less stable & generated first in photolysis : stereospecific addition
triplet methylene – unshared electrons are not paired, free radical (diradical) : nonstereospecific addition

59. Cycloaddition: addition of the carbon – carbon double bond
Sterospecific: (addition of methylene can occur with 2 different kinds of stereochemistry.)
Photolysis of diazomethane into in liquid
And in liquid

60. Singlet methylene
Stereospecific
Electrophilic addition
Electron deficient and
can find electrons at
the C-C double bondingle
Non – stereospecific: cis/trans2 – butene both cis and trans 1,2 -
dimethylcyclopropane
Triplet methylene
Non - Stereospecific
Free radical addition
ff. by addition

61. Methylene undergoes intersection
Addition of substituted carbenes: 1,1 - elimination
Potassium t-butoxide yields cycloalkane

62. Mechanism:
Reaction involves a divalent carbon compound, a derivative of methylene: dichlorocarbene: CU2.
Generated in 2 steps, initiated by attack on chloroform by the strong base tert-butoxide ion and then adds to the alkene.
Because of the presence of halogen atom, the singlet form is the more stable form of dichlorocarbene and is the one adding to the double bond.

63. Addition of Carbenes
Carbenes are intermediates of the general formula CH2:. The derivatives of methylene (CH2) are the carbenes.
Methylene is formed by the photolysis of either diazomethane, CH2N2 or ketene, CH2=C=O.

64. 14. Hydroxylation. Glycol formation
Example.
Oxidizing agents that bring about hydroxylation
cold alkaline potassium permanganate, KMnO4
b. peroxy acids, such as peroxyformic acid HCO2OH

66. 15. Halogenation. Allylic substitution ( same mechanism with substitution in alkenes)
Ex.

68. Can we direct the attack to just one of these sites
Can we direct the attack to just one of these sites? Yes, by our choice of rxn. Conditions.
Conditions:
alkenes undergo substitution by halogen at high temp. or under the influence of UV light, generally in gas phase.
it can also undergo addition of halogen at low temp. in the absence of light and generally in liquid state(phase).

69. N – bromosuccinimide a reagent used for the specific purpose of brominating alkenes at the allylic position provides a constant low conc. of bromine.

70. . Ease of abstraction of hydrogen atoms:
Vinylic hydrogen- hydrogens attached to C=C
Alylic hydrogen – hydrogens attached to a carbon atom next to a double bond
Ease of abstraction of hydrogen atoms:
Allylic >3º > 2º > 1º > CH4 > Vinylic
Ease of formation of free radicals: allyl > 3º > 2º > 1º > CH3. > vinyl

71. Example:

72. 16. Ozonolysis (Cleavege rxn)
Cleavage – a rxn in which the double bond is completely broken and the alkene molecules converted into 2 smaller molecule.
Reducing agent (Zn) – prevent formation of hydrogen peroxide
will not react with aldehyde and ketone (aldehyde are often
converted to acid, RCOOH for ease of isolation.)

74. Ozonolysis – is a typical means of degradation

75. 17. Cleavage with periodate ( cleavage with a diol)
RCOOH are generally obtained instead of aldehydes, RCHO a terminal ==CH2 group is oxidized to CO2.

76. Example.

77. Cleavage of cycloalkenes

78. 18. Epoxidation of Alkenes
C=C +CH3COOH C C CH3COH O
Alkene
Peroxyacetic Acid
Epoxide
Carboxylic acid

79. Example H2C=CH(CH2)9CH3 + CH3COOH CH2-CH(CH2)9CH3 + CH3COH O O
1-Dodecane
Peroxyacetic acid
1,2-epoxydodecane
Acetic acid