Edexcel International A Level (IAL) Chemistry (YCH11) - Unit 4 - 15.9 Nomenclature and structures-Study Notes - New Syllabus
Edexcel International A Level (IAL) Chemistry (YCH11) -Unit 4 – 15.9 Nomenclature and structures- Study Notes- New syllabus
Edexcel International A Level (IAL) Chemistry (YCH11) -Unit 4 – 15.9 Nomenclature and structures- Study Notes -International A Level (IAL) Chemistry (YCH11) – per latest Syllabus.
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Edexcel International A Level (IAL) Chemistry (YCH11) -Concise Summary Notes- All Topics
15.9 Nomenclature and Formulae of Carboxylic Acids
Carboxylic acids are organic compounds containing the carboxyl group:
\( \mathrm{-COOH} \)
The carboxyl group contains both:
- A carbonyl group \( \mathrm{(C=O)} \)
- A hydroxyl group \( \mathrm{(O-H)} \)
General formula:
\( \mathrm{RCOOH} \)
Naming Carboxylic Acids
- Choose the longest carbon chain containing the carboxyl group.
- Replace the alkane ending -e with:
-oic acid
Important Rule
- The carboxyl carbon is always carbon 1.
- Numbering of the carboxyl group is usually unnecessary.
Examples of Names
- \( \mathrm{HCOOH} \) → methanoic acid
- \( \mathrm{CH_3COOH} \) → ethanoic acid
- \( \mathrm{CH_3CH_2COOH} \) → propanoic acid
- \( \mathrm{CH_3CH_2CH_2COOH} \) → butanoic acid
Structural Formulae
Structural formulae show how atoms are connected without displaying every bond.
Examples
- Ethanoic acid:
\( \mathrm{CH_3COOH} \)
- Propanoic acid:
\( \mathrm{CH_3CH_2COOH} \)
Displayed Formulae
Displayed formulae show every atom and bond in the molecule.
Important Features
- Carbonyl double bond shown explicitly.
- Hydroxyl group attached to same carbon.
Skeletal Formulae
- Carbon atoms represented by line ends/intersections.
- Hydrogens attached to carbon omitted.
- Functional group \( \mathrm{-COOH} \) shown clearly.
Examples of Skeletal Structures
- Straight-chain acids shown as zig-zag chain ending in \( \mathrm{COOH} \).
Properties Related to Structure
- Carboxylic acids are polar.
- Can form hydrogen bonds because of \( \mathrm{O-H} \) group.
- Have relatively high boiling points.
Key Naming Points
- Suffix is always -oic acid.
- Carboxyl carbon included in main chain count.
- Carboxyl carbon always carbon 1.
Key Features
- Carboxylic acids contain the \( \mathrm{-COOH} \) group.
- Named using suffix -oic acid.
- Structural, displayed and skeletal formulae must be recognised and drawn.
- Carboxyl carbon is always part of main chain.
Example 1:
Name the compound \( \mathrm{CH_3CH_2CH_2COOH} \).
▶️ Answer/Explanation
The molecule contains four carbon atoms including the carboxyl carbon.
Prefix = butan-.
Suffix for carboxylic acids = -oic acid.
Name:
\( \mathrm{butanoic\ acid} \)
Example 2:
Explain why methanoic acid is classified as a carboxylic acid.
▶️ Answer/Explanation
Methanoic acid contains the \( \mathrm{-COOH} \) functional group.
This group consists of a carbonyl group and hydroxyl group attached to the same carbon atom.
Therefore, it is a carboxylic acid.