1. Alkene
Simple alkenes are named much like alkanes, using the root name of the longest chain containing the double bond. The ending is changed from -ane to -ene. For example, “ethane” becomes “ethene,” “propane” becomes “propene,” and “cyclohexane” becomes “cyclohexene.”

2. In a cis-disubstituted alkene, the vector sum of the two dipole moments is directed perpendicular to the double bond.
In a trans-disubstituted alkene, the two dipole moments tend to cancel out. If an alkene is symmetrically trans disubstituted, the dipole moment is zero.
For example, cis-but-2-ene has a nonzero dipole moment, but trans-but-2-ene has no measurable dipole moment.

3. Alkene Alkanes – saturated CnH2n
Alkenes – unsaturated – not all bonds are saturated
Nomenclature
Common Names –ylene
Ethylene CH2=CH2
Propylene CH2=CH-CH3
Butelene
IUPAC
Replace –ane ending with –ene
Examples - Rules

4. To name alkenes, select the longest carbon chain which includes the carbons of the double bond. Remove the -ane suffix from the name of the alkane which corresponds to this chain. Add the suffix -ene.
2. Number this chain so that the first carbon of the double bond has the lowest number possible.
3-Methyl-3-hexene

5. C=C Double Bond Two bonds One -bond One -bond
sp2 hybridization – planar shape
Bond strength
-bond 108 kcal/mol
-bond kcal/mol (poor overlap of -orbitals)
Weak -bond accounts for functional group character (reactivity of alkenes)

6. Physical Properties of Alkenes
Significant effect of molecular geometry of cis-alkenes on melting points [oC]
Butane –138 trans-2-Butene –106 cis-2-Butene -139
Pentane –130 trans-2-Pentene –135 cis-2-pentene -180
Hexane –95 trans-2-Hexene –133 cis-2-Hexene –141
-bond weak electron-withdrawing character – slight polarity of Cs involved (imbalanced in cis-disubstituted alkenes)

7. Synthesis of Alkenes Dehydrohalogenation of alkyl halides
dehydrohalogenation takes place in one step, in which a strong base abstracts a proton from one carbon atom as the leaving group leaves the adjacent carbon.

8. Formation of the Hofmann Product Bulky bases can also accomplish dehydrohalogenations that do not follow the Zaitsev rule. Steric hindrance often prevents a bulky base from abstracting the proton that leads to the most highly substituted alkene. In these cases, it abstracts a less hindered proton, often the one that leads to formation of the least highly substituted product, called the Hofmann product. The following reaction gives mostly the Zaitsev product with the relatively unhindered ethoxide ion, but mostly the Hofmann product with the bulky tert-butoxide ion.

9. 2. Dehalogenation of vicinal dibromides
Vicinal dibromides (two bromines on adjacent carbon atoms) are converted to alkenes by reduction with iodide ion in acetone.

10. 3. Dehydration of alcohols
Dehydration of alcohols is a common method for making alkenes. The word dehydration literally means “removal of water.”
4. Dehydrogenation of alkanes
Dehydrogenation is the removal of H2 from a molecule

11. 5-Reduction of alkynes

12. 6-Wittig reaction

13. Synthesis of Alkenes
KOH / EtOH
C. H2SO4
1800C
Zn / AcOH

14. Reactions of alkenes
1- Addition of hydrogen halides

15. Electrophilic Addition of HX
Attack of electron-deficient atom at -bond H2C=CH2 + H-I  H2CH-CIH2
Mechanism via Carbocation
Attack of H+ at -bond H2C +-C HH2
I- attacks carbocation
Markovnikov Rule
Proton will attach at less substituted carbon (form the more stable carbocation)
H3CCH=CH2 + H-I  H3CCHI-CHH2
not formed: H3CCHH-CIH2
Carbocation stability: 3o> 2o > 1o > Methyl

16. Radical Additions – Anti-Markovnikov Products
H3CCH=CH2 + H-I  H3CCHI-CHH2
Markovnikov Product
H3CCH=CH2 + H-I  H3CCHH-CIH2
Anti-Markovnikov Product
Caused by contamination of alkene with peroxyradicals (exposure to air)
Mechanism via radicals

19. 2- Acid-catalyzed hydration

20. Alcohol Synthesis – Electrophilic Hydration
Follows Markovnikov rule
Reverse of acid-catalyzed dehydration of alcohols
(H3C) 2CH=CH2 + H-OH  (H3C) 2COH-CH2 (92% yield, Rx in 50% H2O:H2SO4)
Attack of H+ at -bond RC +-C HR
Nucleophilic attack of H2O at Carbocation
Equilibrium: Dependent on Rx conditions
Alcohol  conc. H2SO4 high temp.  Alkene
Alcohol  dil. H2SO4, low temp.  Alkene

21. 3-Hydroboration–oxidation

22. Hydroboration

24. 4- Polymerization

26. 5- Reduction: Catalytic Hydrogenation 6- Addition of Carbenes: Cyclopropanation

27. Oxidation of Alkenes with Peroxycarboxylic Acids
Overall transformation :  C=C to epoxide
Reagent : a peroxycarboxylic acid, RCO3H
Regioselectivity : not relevant since both new bonds are the same, C-O-
Stereoselectivity : syn since the two new C-O s bonds form at the same time from the peroxyacid.

28. 7- Addition of halogens

29. Electrophilic Additions of Halogens to Alkenes
Synthesis of vicinal halides
H2C=CH2 + X2  H2CX-CXH2
Reaction requires no heat or UV light to initiate (as in Alkane halogenation)
Reactivity F>> Cl> Br >>> I
Reaction Mechanism via anti-addition
Polarizable X-X bond leads to heterolytic cleavage - formation of cyclic Bromonium [(+)ive charge] intermediate at double bond

30. 8-Halohydrin formation
9- Epoxidation

31. 10- Ozonolysis

33. 11- Potassium permanganate

35. Reactions of alkenes H2 / Pd X= Cl, Br, I X= Cl, Br or Ni CCl4 CCl4 O3+
Zn / H2O
KMnO4 /OH or
X2 / H2O