Aldehydes and ketones

Made using OCR Chemistry textbook. Pages 20- 27. Gent and Richie.

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  • Created by: M
  • Created on: 27-12-12 17:01
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  • Aldehydes and ketones
    • Functional group: C=O bond
      • comprises of sigma and pi- bond
        • pi bond= overlap of p orbitals on O and C atoms.
      • O atom is more electronegative = dipole in C=O bond as e- more attracted to O
      • Functional group= part of organic molecule thats responsible for its chemical reactions
    • Naming
      • Aldehydes: end in -al
      • Ketones: end in -one
        • Parent chain= longest chain containing C=O. Numbered so smallest number is used.
    • Aromatic aldehydes and ketones
      • Compounds containing both a benzene ring and a carbonyl group
        • Benzaldehyde (almond)
        • Phenylethanone
    • Oxidation
      • Oxidising mixture of potassium dichromate and sulphuric acid
        • Orange to  green
        • Primary alcohol to aldehyde, secondary to ketone
      • Ketone cannot be oxidised further
      • Aldehyde oxidised to a carboxylic acid
    • Reduction
      • Reverses oxidation, i.e. aldehyde back to primary alcohol etc.
    • Testing
      • 1. Detecting presence of carbonyl group
        • Use  Brady's reagent (solution of 2,4-DNPH)
          • Orange precipitate forms
            • Only +ve for aldehydes & ketones
            • 3. Identify
              • Precipitate: filter, purify, recrystallise, measure m.p., compare to known values.


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