Naming Alkynes Using IUPAC System

Recognition of Alkynes

• Alkynes feature a carbon-carbon triple bond (two pi bonds between the same two carbons).
• The carbon holding the alkyne is sp hybridized.
  • Bond angle: 180 degrees
  • Molecular shape: Linear

Example of a Simple Alkyne

• Consider C≡C−H (known as acetylene).
• Compare with a two-carbon alkane (H-C-C-H with additional hydrogens).
• Alkyne has a hydrogen deficiency index of 2 (formula: CnH2n-2).
• Alkanes have the formula CnH2n+2.

Drawing Alkynes

• Bond angle must be 180 degrees – draw as a straight line.
• Triple bond starts and ends on two carbons.
• Include additional carbons on the ends of the chain.

Naming Alkynes

• Follow standard IUPAC naming rules.
• Identify the Parent Chain
  • Number the chain starting closest to the alkyne.
  • Total number of carbons determines the base name (e.g., "bute" for 4 carbons).
• Indicate the Triple Bond
  • Add "yne" as a suffix (e.g., "2-butyne").
  • Number indicates the position of the triple bond.

Examples

1. 2-Butyne

   • Alkyne in the middle of a 4-carbon chain.
   • Number from the direction that gives the lowest position to the triple bond.

2. 1-Pentyne

   • Terminal alkyne (triple bond at end of chain).
   • Number from the side giving the lowest number to the triple bond.

3. 2-Methyl-5-Heptyne

   • Substituted alkyne.
   • Prioritize substituents and triple bonds when numbering.
   • Methyl group on carbon 2, triple bond on carbon 5.

Diynes

• Compounds with two carbon-carbon triple bonds.
• Example: Terminal alkyne on a chain with 7 carbons.
  • Naming: First name based on the number of carbons ("hept").
  • Use "diyne" to indicate two triple bonds.
  • Include positions of both triple bonds (e.g., 1,5-heptadiyne).

Special Naming Rule

• If the numbers and "yne" prefix create a consonant clash (e.g., 1,5-heptadiyne), insert an "a" for flow.

Further Learning

• For more guidance, download the ebook "10 Secrets to Acing Organic Chemistry."
• Online tutoring information available at "layoversai.com/orgtutor."

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