Edexcel International A Level (IAL) Chemistry (YCH11) - Unit 4 - 15.6 Nomenclature and structures-Study Notes - New Syllabus

Edexcel International A Level (IAL) Chemistry (YCH11) -Unit 4 – 15.6 Nomenclature and structures- Study Notes- New syllabus

Edexcel International A Level (IAL) Chemistry (YCH11) -Unit 4 – 15.6 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

15.6 Nomenclature and Formulae of Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds containing the carbonyl group:

\( \mathrm{C=O} \)

They differ in the position of the carbonyl group within the molecule.

Aldehydes

  • Carbonyl group is at the end of the carbon chain.
  • General formula:

\( \mathrm{RCHO} \)

Ketones

  • Carbonyl group is within the carbon chain.
  • General formula:

\( \mathrm{RCOR’} \)

Naming Aldehydes

  • Choose the longest carbon chain containing the aldehyde group.
  • Replace the alkane ending -e with:

-al

  • Aldehyde carbon is always carbon 1, so numbering is usually unnecessary.

Examples

  • \( \mathrm{HCHO} \) → methanal
  • \( \mathrm{CH_3CHO} \) → ethanal
  • \( \mathrm{CH_3CH_2CHO} \) → propanal

Naming Ketones

  • Choose the longest chain containing the carbonyl group.
  • Replace the alkane ending -e with:

-one

  • Number the chain to give the carbonyl carbon the lowest possible number.

Examples

  • \( \mathrm{CH_3COCH_3} \) → propanone
  • \( \mathrm{CH_3COCH_2CH_3} \) → butan-2-one

Structural Formulae

Shows how atoms are connected without displaying every bond.

Examples

  • Ethanal:

\( \mathrm{CH_3CHO} \)

  • Propanone:

\( \mathrm{CH_3COCH_3} \)

Displayed Formulae

Show every atom and bond in the molecule.

Example Principles

  • Carbonyl group drawn explicitly as:

\( \mathrm{C=O} \)

  • All hydrogen atoms shown.

Skeletal Formulae

  • Carbon atoms represented by line ends/intersections.
  • Hydrogen atoms attached to carbon omitted.
  • Functional groups shown clearly.

Important Naming Rules

  • Aldehyde carbon always terminal.
  • Ketones require numbering for carbonyl position.
  • Carbonyl carbon counts as part of main chain.

Key Features

  • Aldehydes contain terminal \( \mathrm{C=O} \).
  • Ketones contain internal \( \mathrm{C=O} \).
  • Aldehydes use suffix -al.
  • Ketones use suffix -one.
  • Must be able to draw structural, displayed and skeletal formulae.

Example 1:

Name the compound \( \mathrm{CH_3CH_2COCH_3} \).

▶️ Answer/Explanation

Longest chain has four carbons → butane.

Carbonyl group is on carbon 2.

Suffix is -one.

Name:

\( \mathrm{butan\text{-}2\text{-}one} \)

Example 2:

Explain why propanal is classified as an aldehyde and not a ketone.

▶️ Answer/Explanation

In propanal, the carbonyl group is at the end of the carbon chain.

The carbonyl carbon is bonded to a hydrogen atom.

Therefore, it is an aldehyde.

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