20.1 Naming Carboxylic Acids and Nitriles

Carboxylic acids and nitriles are key players in organic chemistry. These compounds have unique structures and naming conventions that set them apart. Understanding their nomenclature is crucial for identifying and working with these important molecules.

IUPAC naming rules provide a systematic approach to naming these compounds. For carboxylic acids, the -oic acid ending is key, while nitriles use the -nitrile suffix. Common names are still used for simple acids, and acyl groups play a role in naming acid derivatives.

Carboxylic Acids and Nitriles

IUPAC naming of carboxylic acids

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• Identify the longest carbon chain containing the carboxyl group (-COOH) as the parent chain
• Replace the -e ending of the corresponding alkane with -oic acid to indicate the presence of a carboxylic acid functional group
• Number the carbon chain starting from the carboxyl carbon to give the lowest possible numbers to substituents
• Indicate the positions and names of any substituents using numbers and prefixes (2-methylpentanoic acid)
• Common names for simple carboxylic acids still widely used (examples of functional groups)
  • Formic acid (HCOOH), simplest carboxylic acid
  • Acetic acid (CH3COOH), found in vinegar
  • Propionic acid (CH3CH2COOH), used as a preservative
  • Butyric acid (CH3CH2CH2COOH), responsible for the smell of rancid butter
• Acyl groups (RCO-) derived from carboxylic acids by removing the -OH group
  • Named by replacing the -ic acid ending with -yl (acetyl, propionyl, butyryl)
  • Represent the carboxylic acid minus the hydroxyl group
  • Used in naming acid derivatives (acetyl chloride, propionyl bromide)

Nomenclature of nitriles

• Nitriles contain the -CN functional group, a carbon atom triple-bonded to a nitrogen atom
• IUPAC nomenclature for nitriles
  • Identify the longest carbon chain containing the -CN group as the parent chain
  • Replace the -e ending of the corresponding alkane with -nitrile (pentanenitrile)
  • Number the carbon chain starting from the nitrile carbon to give the lowest possible numbers to substituents
  • Indicate the positions and names of any substituents using numbers and prefixes (2-methylbutanenitrile)
• Prefix nomenclature for nitriles
  • Use the prefix cyano- to indicate the presence of a -CN group
  • Name the parent compound as usual (based on the longest carbon chain)
  • Indicate the position of the -CN group using numbers (2-cyanopentane)

Structures from acid and nitrile names

• Drawing carboxylic acids
  1. Identify the parent alkane from the name (pentane from pentanoic acid)
  2. Replace the -oic acid ending with a carboxyl group (-COOH) at the end of the chain
  3. Attach any substituents at the indicated positions (2-methylpentanoic acid has a methyl group on the second carbon)
• Drawing nitriles (IUPAC)
  1. Identify the parent alkane from the name (butane from butanenitrile)
  2. Replace the -nitrile ending with a -CN group at the end of the chain
  3. Attach any substituents at the indicated positions (2-methylbutanenitrile has a methyl group on the second carbon)
• Drawing nitriles (prefix)
  1. Draw the structure of the parent compound (pentane for 2-cyanopentane)
  2. Attach a -CN group at the position indicated by the number preceding the cyano- prefix (2-cyanopentane has the -CN on the second carbon)

IUPAC Nomenclature and Common Names

• IUPAC nomenclature provides systematic naming rules for organic compounds
• Common names are still widely used for some simple compounds
• Substituents are groups attached to the parent chain and are named using prefixes
• Functional groups determine the compound's class and are prioritized in naming