1. Chapter 3 Adel M. Awadallah Islamic University of Gaza
Organic chemistry for medicine and biology students
Chem 2311
Chapter 3
Alkenes and Alkynes
By Prof. Dr.
Adel M. Awadallah
Islamic University of Gaza

2. Hydrocarbons (contain only carbon and hydrogen)
Alkenes and Alkynes
Hydrocarbons (contain only carbon and hydrogen)
Saturated: (Contain only single bonds)
Alkanes (CnH2N + 2 )
Cycloalkanes (CnH2N )
b) Unsaturated: contain
Alkenes: double bonds (,,,CnH2N)
Alkynes: triple bonds ((CnH2N - 2)
Aromatic: benzene like compounds

3. Facts about double and triple bonds

4. Nomenclature of alkenes and Alkynes
The ending ene is used for alkenes and yne for alkynes
Select the longest chain that includes both carbons of the multiple bond
Number the chain from the end nearest to the multiple bond
Indicate the position of the multiple.
Examples

5. Isomers and common names of simple alkenes

6. Assigning Priority
Alkenes and alkynes are considered to have equal priority
In a molecule with both a double and a triple bond, whichever is closer to the end of the chain determines the direction of numbering.
In the case where each would have the same position number, the double bond takes the lower number.
In the name, “ene” comes before “yne” because of alphabetization.

8. Compounds containing more than one double bond

9. Cis-Trans (Z-E) Isomerism in Alkenes
If each end of the double bond is attached to two different groups, then the compound exists in two different forms called (Diastereomers; These are non mirror image stereoisomers).
If the two groups are identical we distinguish the two isomers by adding the prefix cis (same side) or trans (opposite sides)
Example

10. If the groups attached to the double bond are different, we distinguish the two isomers by adding the prefix Z (same side) or E (opposite sides) depending on the atomic number of the atoms attached to each end of the double bond

13. Hydrogen is a symmetric reagent

16. Bromine is a symmetric reagent

20. Water is unsymmetric reagent

22. Acid Catalized Hydration of Alkenes

24. Rearrangement of Carbocations

29. Addition of HBr (Unsymmetric reagent):