1 / 14

Alkenes

Alkenes. Lec.4. Alkenes( Olefins ). Hydrocarbons that contain a carbon–carbon double bond are called alkenes. General formula C n H 2 n . Unsaturated , because they contain fewer hydrogens per carbon than alkanes The simplest alkene is ethylene(H2C  CH2).

umeko
Download Presentation

Alkenes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Alkenes Lec.4

  2. Alkenes(Olefins) • Hydrocarbons that contain a carbon–carbon double bond are called alkenes. • General formula CnH2n. • Unsaturated, because they contain fewer hydrogens per carbon than alkanes • The simplest alkene is ethylene(H2C  CH2)

  3. The physical properties of Alkenes: Because alkenes are essentially nonpolar compounds and the only attractive forces between their molecules are dispersion forces, their physical properties are similar to those of alkanes.

  4. Nomenclature:(A) IUPAC • The IUPAC rules for naming alkenes are similar to those for alkanes, but a few rules must be added for naming and locating the multiple bonds. • The ending -eneis used to designate a carbon–carbon double bond. When more than one double bond is present, the ending is -diene, -triene, and so on. • Select the longest chain that includes both carbons of the double.

  5. 3. Number the chain from the end nearest the multiple bond so that the carbon atoms in that bond have the lowest possible numbers. NOTE: If the multiple bond is equidistant from both ends of the chain, number the chain from the end nearest the first branch point. 4. Indicate the position of the multiple bond using the lower numbered carbon atom of that bond

  6. 5. If more than one multiple bond is present, number the chain from the end nearest the first multiple bond. EXAMPLE(1):

  7. EXAMPLE(2):

  8. NOTE:

  9. EXAMPLE (3): Write the structural formula for 3-methyl-2-pentene. SOLUTION: In this case, note that the chain has five carbons and that the double bond is located between carbon-2 and carbon-3:

  10. PROBLEMS: Draw the structure for each of the following compounds: 3,3-dimethylcyclopentene b. 6-bromo-2,3-dimethyl-2-hexene

  11. (B)Common Method: • Rules for common names are the same as alkanes except that the ending (ylene) is used instead of (ane): • Ethane CH3­ – CH3 → ethylene CH2 = CH2 • Propane CH3 – CH2 – CH3 → propylene CH2 = CH – CH3

  12. Cis–Trans Isomerism • Because rotation at carbon–carbon double bonds is restricted, cis–trans isomerism (geometric isomerism) is possible in appropriately substituted alkenes. Cis: In cis, trans-alkene nomenclature, it refers to molecules in which the carbon atoms of the main chain are on the same side of the double bond. Trans: In cis, trans-alkene nomenclature, it refers to molecules in which the carbon atoms of the main chain are on opposite sides of the double bond.

  13. For example: 1,2-dichloroethene exists in two different forms:

  14. EXAMPLE: Are cis–trans isomers possible for 1-butene and 2-butene? Solution : 2-Butene has cis–trans isomers, but 1-butene does not. For 1-butene, carbon-1 has two identical hydrogen atoms attached to it; therefore, only one structure is possible.

More Related