Overview
This lecture covers the naming of alcohols using both common and IUPAC nomenclature, highlighting key rules and priority for functional groups, multiple substituents, and cyclic structures.
Common Names of Alcohols
- CH₃OH is called methyl alcohol (methanol).
- CH₃CH₂OH is called ethyl alcohol (ethanol).
- (CH₃)₂CHOH is isopropyl alcohol.
- (CH₃)₃COH is tert-butyl alcohol.
IUPAC Nomenclature Principles
- The parent chain includes the longest carbon chain containing the OH group.
- Replace the “-e” in the alkane name with “-ol” to indicate an alcohol.
- Number the carbon chain to give the OH group the lowest possible number.
- For isopropyl alcohol: propan-2-ol (2-propanol).
- For tert-butyl alcohol: 2-methyl-2-propanol.
Naming with Multiple OH Groups
- Use “-diol”, “-triol” for two or more OH groups.
- Example: 3,4-hexanediol for a six-carbon chain with OH on carbons 3 and 4.
Substituents and Priority Rules
- Alcohols take naming priority over alkyl halides (e.g., bromine).
- Number to give the OH group the lowest number; substituents are numbered and named alphabetically.
- Example: 4-bromo-1-pentanol (OH on carbon 1, Br on carbon 4).
- Place substituent numbers in ascending order after alphabetizing.
Condensed Structures and Methoxy Groups
- Convert condensed to line/expanded structure for clarity.
- The hydroxy (OH) group has naming priority over methoxy (OCH₃) groups.
- Example: 4-methoxy-1-butanol (methoxy on carbon 4, OH on carbon 1).
Naming Alcohols on Rings
- For a single OH group: Numbering starts on the carbon with OH; specify "cycloalkanol".
- No need to state "1-cycloalkanol" unless there are other substituents.
- For substituents: Alphabetize and number to give lowest possible numbers.
- Example: 3-ethylcyclohexanol (ethyl on carbon 3).
Multiple Substituent Numbering on Rings
- Choose numbering to give the lowest sum of substituent numbers.
- Example: 2-ethyl-5-methylcyclohexanol (ethyl on 2, methyl on 5, OH on 1).
Key Terms & Definitions
- Alcohol — Organic compound with an OH (hydroxyl) group attached to a saturated carbon.
- Parent chain — The longest continuous carbon chain containing the functional group.
- Substituent — An atom or group attached to the parent chain not part of the main chain.
- Diol/Triol — Compounds with two/three hydroxyl groups.
- Cycloalkanol — A cyclic compound containing an alcohol group.
Action Items / Next Steps
- Practice naming additional alcohols, including those with multiple substituents and rings.
- Review assigned textbook problems on alcohol nomenclature.