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🥼Organic Chemistry Unit 17 Review

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17.1 Naming Alcohols and Phenols

🥼Organic Chemistry
Unit 17 Review

17.1 Naming Alcohols and Phenols

Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
🥼Organic Chemistry
Unit & Topic Study Guides

Naming Alcohols

IUPAC Naming of Alcohols

Naming alcohols follows a systematic process. The hydroxyl group (-OH) is the defining feature, and IUPAC rules make sure every name points to one specific structure. Here's how to build the name step by step:

  1. Find the longest carbon chain that includes the carbon bonded to the -OH group. If two chains of equal length qualify, pick the one with more substituents.

  2. Number the chain starting from the end nearest to the hydroxyl group, so the -OH gets the lowest possible number.

  3. Classify the alcohol by how many other carbons are attached to the carbon bearing the -OH:

    • Primary (1°): one carbon attached (e.g., 1-propanol)
    • Secondary (2°): two carbons attached (e.g., 2-butanol)
    • Tertiary (3°): three carbons attached (e.g., 2-methyl-2-propanol)

  4. Replace the "-e" ending of the parent alkane name with "-ol" to indicate the hydroxyl group.

  5. Add a locant (position number) for the -OH group right before the "-ol" suffix.

  6. Name and number all substituents, then list them alphabetically as prefixes.

Putting it all together, the final name reads: substituent locants and names (alphabetical), then the parent chain name with the -OH locant and "-ol" suffix. For example, 3-methyl-1-butanol tells you there's a methyl group on carbon 3 and a hydroxyl group on carbon 1 of a four-carbon chain.

IUPAC naming of alcohols, Functional Groups | Introduction to Chemistry

Hydroxyl Group Positioning in Alcohols

Getting the -OH position right is the most important part of naming an alcohol, because it determines the locant that appears in the name.

  • Number the chain so the -OH carbon gets the lowest possible number. This takes priority over giving substituents low numbers.
  • If the -OH is equidistant from both ends, break the tie by numbering from the end that gives substituents the lowest set of locants (e.g., 2,3-dimethyl-2-butanol).
  • Multiple hydroxyl groups: use "-diol" for two, "-triol" for three, and so on. Include a locant for each -OH (e.g., 1,2-ethanediol, commonly known as ethylene glycol).
  • When a higher-priority functional group is present (such as a carboxylic acid or aldehyde), that group dictates the suffix. The -OH is then treated as a substituent using the prefix "hydroxy-" instead of the "-ol" suffix. For example, 3-hydroxybutanoic acid has both an -OH and a -COOH, but the carboxylic acid takes naming priority.

Keep in mind that different positions of the -OH group on the same carbon skeleton produce constitutional isomers with distinct physical and chemical properties (e.g., 1-propanol vs. 2-propanol).

IUPAC naming of alcohols, Alcohols and Ethers · Chemistry

Naming Phenols

Phenol Nomenclature vs. Aromatics

A phenol is a benzene ring with a hydroxyl group bonded directly to the ring carbon. This direct attachment to an aromatic ring makes phenols behave quite differently from ordinary alcohols, but the naming process is straightforward.

  1. Identify the benzene ring bearing the -OH group. If -OH is the only substituent, the compound is simply called phenol.
  2. Number the ring starting from the carbon bonded to the -OH (carbon 1). Go clockwise or counterclockwise, whichever direction gives substituents the lowest set of locants.
  3. Name and number each substituent, then list them alphabetically before "phenol."

For example, a phenol with a chlorine on carbon 2 and a methyl group on carbon 4 is named 2-chloro-4-methylphenol.

If the ring carries a functional group with higher naming priority than -OH (like -COOH or -CHO), the compound is named as a derivative of that group, and the hydroxyl becomes the prefix "hydroxy-". For instance, 4-hydroxybenzoic acid has both an -OH and a carboxylic acid on the ring, but the acid takes the suffix.

Functional Groups and Organic Acids

  • The hydroxyl group (-OH) defines both alcohols and phenols, but context matters: in alcohols it's bonded to a saturated carbon, while in phenols it's bonded directly to an aromatic ring. This difference affects acidity, reactivity, and physical properties.
  • Carboxylic acids contain a carboxyl group (-COOH) and are significantly more acidic than alcohols or phenols. When -COOH is present in the same molecule as -OH, the carboxylic acid group takes naming priority.
  • Recognizing which functional group is present (and which has higher priority) is essential for choosing the correct suffix and predicting how the molecule will behave in reactions.