Carbonyl Compounds
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Carbonyl Compounds

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Revision of carbonyl compounds

Revision of carbonyl compounds

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Carbonyl Compounds Carbonyl Compounds Presentation Transcript

  • Carbonyl Compounds Aldehydes and Ketones
  • Contents
    • Aldehydes vs. Ketones
    • Testing for Carbonyl Compounds
    • Distinguishing Between Aldehydes and Ketones  Mild Oxidation
    • Oxidation of Aldehydes (Primary Alcohols)
    • Oxidation of Ketones (Secondary Alcohols)
    • Neucleophilic Addition Reaction
    • Definitions
    • Summary
  • Aldehydes vs. Ketones
    • The functional group is: >C=O
    • Polar bond
    • The aldehyde has the functional group attached to one carbon
    • Suffix = -al
    • Oxidation of primary alcohols
    • Has a low boiling point
    • Soluble in water
    • The functional group is:
    • >C=O
    • Polar bond
    • The ketone has the functional group attached to two carbon
    • Suffix = -one
    • Oxidation of secondary alcohols
    • Has a low boiling point
    • Soluble in water
    Back to Contents
  • Testing for Carbonyl Compounds
    • Brady’s reagent or a 2,4-DNPH solution
    • When added to a carbonyl compound it produces a yellow-orange precipitate
    • Works with ketones and aldehydes
    • Does not work with carboxylic acids, esters, esters, acid clorides and amides which contains the >C=O group
    • Find the boiling point of the precipitate and the identity of the carbonyl compound can be found
    Back to Contents
  • Distinguishing Between Aldehydes and Ketones  Mild Oxidation
    • Tollen's Reagent
    • Involves a ammoniacal silver nitrate solution
    • A aldehyde or ketone is shaken with the ammoniacal silver nitrate solution
    • If there is an aldehyde then the test tube will form a “silver mirror”  silver precipitate
    • This is due to the silver ion being reduced
    • The silver may be formed as a black precipitate
    • This works with all aldehydes
    • Fehling's Reagent
    • Involving copper (II) ions
    • When added to a aldehyde and placed into a water bath, it will form a red precipitate
    • The red precipitate is Cu₂O
    • But it only works with aliphatic aldehydes
    In both tests the aldehyde is oxidised to a carboxylate salt Tollen’s Reagent is better because it works with all aldehydes. Both don’t work with ketones but vigorous oxidation will work Back to Contents
  • Oxidation of Aldehydes (Primary Alcohols)
    • Mild oxidation
    • CH₃CH₂OH (l) [O]  CH₃CHO (l) + H₂O(l)
    • This is done by distillation
    • CH₃CHO (l) + [O]  CH₃COOH (l)
    • This is done by refluxing
    • Easily oxidised to acids unlike ketones
    Back to Contents
  • Oxidation of Ketones (Secondary Alcohols)
    • CH₃CHOHCH₃ (l) + [O]  CH₃OCOCH₃ (l) + H₂O
    • C₂HCOCH₂CH₃ (l) + 3[O]  C₂HCOOH (l) + CH₃COOH (l)
    • Only oxidised under vigorous conditions to acids
    Back to Contents
  • Neucleophilic Addition Reaction
    • Occurs with both aldehydes and ketones
    • Reagent: NaBH₄
    • Conditions: Aqueous/ alcoholic solution
    • Nucleophile: H⁻
    • CH₃CHO + 2[H]  CH₃CH₂OH
    • CH₃COCH₃ + 2[H]  CH₃CHOHCH
    • Mechanism:
    Primary alcohol Secondary alcohol Back to Contents
  • Definitions
    • Redox reaction – both reduction and oxidation take place
    • Reflux – continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry
    • Neucleophile – an atom or group of atoms attracted to an electron-deficient centre, where it donates a pair of electrons to form a new covalent bond
    • Functional group – the part of an organic molecule responsible for its chemical reactions
    • Electronegativity – a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
    • Stem – the longest carbon chain present in an organic molecule
    • Suffix – the part of the name added after the stem
    Back to Contents
  • Summary Back to Contents Aldehyde Reacts with 2,4-DNP(H) Yellow/orange precipitate Reduced to Primary alcohol Oxidised to Carboxylic acid Ketones Reacts with 2,4-DNP(H) Yellow/orange precipitate Reduced to Secondary alcohol Not oxidised