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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) Saturated: (Contain only single bonds) Alkanes (C n H 2N + 2 )
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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) • 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
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
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.
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