Overview
This lecture covers how to name alkynes using both common names and IUPAC nomenclature, including various examples and rules for prioritizing functional groups.
Common Naming of Alkynes
- Acetylene (C≡CH) is the simplest alkyne; its common name is acetylene.
- Adding a methyl group: methyl acetylene (CH₃C≡CH).
- Two methyl groups: dimethyl acetylene.
- Adding an ethyl group: ethyl acetylene (CH₃CH₂C≡CH).
- Phenyl group attached: phenylacetylene (phenyl + acetylene).
- Two phenyl groups: diphenylacetylene.
- Two isopropyl groups: diisopropylacetylene.
- For common names, list alkyl groups alphabetically before "acetylene", written as one word.
IUPAC Nomenclature of Alkynes
- Identify the longest carbon chain containing the triple bond.
- Number the chain to give the triple bond the lowest possible number.
- Replace "-ane" with "-yne"; indicate the position of the triple bond (e.g., but-1-yne for a four-carbon chain with a triple bond at carbon 1).
- Name and number substituents; list them alphabetically.
- When multiple triple bonds: use "-diyne," "-triyne," etc. (e.g., 1,5-nonadiyne).
- Triple bond gets priority in numbering over alkyl and halogen substituents.
Functional Group Priority in Naming
- Triple bond (alkyne) takes priority over alkyl and halo substituents in numbering.
- Alkene (double bond) has higher priority than alkyne; number to give the alkene the lowest number.
- Alcohol group (–OH) has higher priority than alkyne; number chain to give the alcohol the lowest number.
Key Terms & Definitions
- Alkyne — Hydrocarbon with at least one carbon-carbon triple bond (–C≡C–).
- Acetylene — The simplest alkyne (C₂H₂ or HC≡CH).
- IUPAC Name — Systematic chemical name following International Union of Pure and Applied Chemistry rules.
- Common Name — Traditional or simpler name, often based on "acetylene" plus substituent names.
- Phenyl — The substituent derived from benzene (C₆H₅–).
- Isopropyl — The substituent derived from propane (–CH(CH₃)₂).
Action Items / Next Steps
- Practice naming more alkyne examples using both common and IUPAC methods.
- Review functional group priority in nomenclature.
- Complete any assigned exercises or textbook readings on alkynes.