Alkene and Alkynes..pdf

Medical Chemistry Almaaqal University Collage of Dentistry Alkenes and Alkynes Dr/ Wael Sobhy Darwish Lec-10 1ST stage&2024 Definition Alkene and A...

Medical Chemistry Almaaqal University Collage of Dentistry Alkenes and Alkynes Dr/ Wael Sobhy Darwish Lec-10 1ST stage&2024 Definition Alkene and Alkynes Alkenes: an unsaturated hydrocarbon that contain one or more carbon–carbon double bonds Ethene (ethylene) is the simplest alkene. Alkynes: an unsaturated hydrocarbon that contain one or more carbon–carbon triple bonds. Ethyne (acetylene) is the simplest alkyne:  Alkenes Alkenes are sometimes called olefins General Formula:- CnH2n Functional group :- Carbon-carbon double bond Unsaturated due to the = double bond Why isn’t there a methene? CH2 = CH2 CH3CH = CH2 CH3CH2CH = CHCH3  Alkynes General Formula:- CnH2n-2 Functional group :- Carbon-carbon triple bond  Naming alkenes and Alkynes STEP 1: Name the main chain. Find the longest continuous chain of carbons containing the double or triple bond. The names of alkenes end with –ene, and the names of alkynes end with –yne. STEP 2: Number the carbon atoms in the main chain. Begin at the end nearer the multiple bond. If the multiple bond is at the same distance from both ends, begin numbering at the end nearer the first branch point.  Physical Properties of Alkenes and Alkynes Alkenes and alkynes are nonpolar compounds, and the only attractive forces between their molecules are dispersion forces. Therefore, their physical properties are similar to those of alkanes with the same carbon skeletons. They do not dissolve in water. Instead, they form two layers when mixed with water or another polar organic liquid such as ethanol.  Preparation of alkene Alcohol Dihalide Alkyl halide Alkyne Saytzeff rule :- Elimination of H is taken from the carbon containing less number of hydrogen atoms Reactions of Alkenes Hydrogenation Halogenation Hydration Polymerisation Ozonolysis  Hydrogenation In this reaction, the double bond is broken, and two extra hydrogen molecules are added to the molecule. H2 gas is used to achieve this, along with a nickel catalyst that helps lower the activation energy of the reaction.  Halogenation In halogenation reactions, the double bond of the alkene is broken in a manner similar to hydrogenation. However, instead of adding two molecules of hydrogen, a halogen substituent is bonded to the carbon atom.  Hydration The hydration reaction is what turns alkenes into alcohols. Sulphuric acid and water are mixed with an alkene to form the corresponding alcohol. The figure shows the conversion of ethene to ethanol.  Polymerisation Polymerisation reactions are one of the most commercially used reactions of alkenes and are how all plastics are made. The most basic example of this reaction occurs between molecules of ethene. Polymerisation of ethene to form polyethylene.  Ozonolysis Ozonolysis is the most complicated reactions and one of the most useful. In this reaction, ozone gas, which is an important part of the earth's atmosphere, is added to an alkene. The mixture splits the alkene at the double bond into two molecules with a carbon compound double bonded to an oxygen. This is also known as a carbonyl compound. Ozonolysis of an alkene to form two carbonyl products  Uses of alkenes Alkenes are extremely useful in manufacturing industrial chemicals and pharmaceuticals. They can even be used to make alcohol and many kinds of plastic, including polystyrene and PVC. Alkenes are also found in important natural substances, such as vitamin A and rubber. Even ethene, the simplest alkene, has an important role in the ripening of fruit.