Organic chemistry for medicine and biology students Chem

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

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

Facts about double and triple bonds

Nomenclature of alkenes and Alkynes 1) 2) 3) 4) 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

Isomers and common names of simple alkenes

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.

Compounds containing more than one double bond

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

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

Hydrogen is a symmetric reagent

Bromine is a symmetric reagent

Water is unsymmetric reagent

• Addition of HBr (Unsymmetric reagent):