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Understanding Alkenes, Alkynes & Aromatic Compounds

Learn about unsaturated hydrocarbons, bond angles, naming conventions, and examples of alkenes and alkynes with detailed explanations and examples.

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Understanding Alkenes, Alkynes & Aromatic Compounds

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  1. Chapter 12 Alkenes, Alkynes, and Aromatic Compounds 12.1Alkenes and Alkynes

  2. Unsaturated Hydrocarbons Unsaturated hydrocarbons • have fewer hydrogen atoms attached to the carbon chain than do alkanes • are alkenes with double C=C bonds • are alkynes with triple C≡Cbonds

  3. Bond Angles in Alkenes According to VSEPR theory: • Three groups in a double bond are bonded at 120° angles. • Alkenes are flat because the atoms in a double bond lie in the same plane.

  4. Bond Angles in Alkynes According to VSEPR theory: • The atoms in a triple bond have a 180° angle.

  5. Naming Alkenes The names of alkenes • use the corresponding alkane name • change the ending from -ane to -ene Alkene IUPAC Common H2C=CH2 Ethene Ethylene H2C=CH─CH3 Propene Propylene Cyclohexene

  6. Ethene (Ethylene) Ethene, or ethylene, • is the alkene C2H4 • has two carbon atoms connected by a double bond • has two H atoms bonded to each C atom • is flat with all the C and H atoms in the same plane • is used to accelerate the ripening of fruits

  7. Naming Alkynes The names of alkynes • use the corresponding alkane name • change the ending from -ane to -yne Alkyne IUPAC Common HC≡CH Ethyne Acetylene HC≡C─CH3 Propyne

  8. Guide to Naming Alkenes and Alkynes

  9. Example of Naming Alkenes Write the IUPAC name for CH2═CH─CH2─CH3 and CH3─CH≡CH─CH3. STEP 1Name the longest carbon chain with a double of triple bond: butene, butyne STEP 2Number the chain from the end nearer the double or triple bond: CH2═CH─CH2─CH3 1 2 3 4 CH3─CH≡CH─CH3 1 2 3 4 STEP 3Give the location and name of the double or triple bond. 1-butene 2-butyne

  10. Names for Alkanes, Alkenes, and Alkynes

  11. Examples of Naming Alkenes with Substituents Write the IUPAC name for STEP 1Name the longest carbon chain: pentene STEP 2Number the chain from the end nearer the double or triple bond: STEP 3Give the location and name of the substituent and double or triple bond: 4-methyl-2-pentene

  12. Naming Alkynes with Substituents Write the IUPAC name for STEP 1Name the longest carbon chain: butyne STEP 2Number the chain from the triple bond: STEP 3Give the location and name of the substituent and double or triple bond:3-Methyl-1-butyne

  13. Learning Check Write the IUPAC name for each of the following:

  14. Solution Write the IUPAC name for each of the following: 1-butene 2-butene 2-methyl-2-butene 4-methyl-2-pentyne

  15. Learning Check Draw the condensed structural formula for each of the following: A. 2-Hexyne B. 3-Methyl-3-hexene

  16. Solution Draw the condensed structural formula for each of the following: A. 2-hexyne B. 3-methyl-3-hexene

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