CARBONYL COMPOUNDS
carbonyl cpds: ketones + aldehydes
MF: C_nH_2nO
functional group: aldehyde: R-C=(O)H, ketone: R-C(=O)-R

Physical properties
-methanal: only carbonyl cpd gas at rtp
-aldehydes: strong, pungent smell
-ketones: pleasant smell
-polar bonds > permanent dipole-dipole attraction > higher mp, bp than expected
-lower members of carbonyl cpds: soluble in H₂O, higher members (stronger attraction) > only in organic solvents

Formation of carbonyl cpds
aldehydes:
oxidation of 1° alcohols
condition: heat + distil

ketones:
oxidation of 2° alcohols
condition: heat under reflux


Nucleophilic addition to carbonyl group
O atom draws e^-s from C atom > polar bond, C atom δ+
-ve nucleophile attaches to C atom

reagent: conc sol of aq KCN [KCN > K⁺ + CN^-, H₂O OH^- + H⁺ => H⁺ + CN^- HCN]
condition: room temp

Mechanism of nuclephilic addition


Condensation reaction
reagent: 2,4-denitrophenylhydrazine (dissolved in aq alcoholic solvent > orange yellow sol)
condition: room temp

observation: immediate orange-yellow precipitate formed

Reduction to alcohol
reagent: LiAlH₄
condition: ice-cold temp (0°C -10°C)
R-C(=O)H + 2[H] >(LiAlH₄/dry ether, < 10°C)> R-CH₂OH

Triodomethane test
reagent: alkaline aq I sol
condition: warm reaction mixture

observation: yellow ppt of CHI₃

Reactions to test for aldehydes
Tollen's Reagent reagent: diammine silver ion in alkaline sol (Tollen's reagent) (colourless)
[preparation of Tollen's reagent:
  NaOH(aq) + AgNO₃(aq) > AgOH(s)(brown ppt)
  AgOH(s) + 2NH₃(aq)(excess) > Ag(NH₃)₂⁺(aq) + OH^-(aq)]
condition: warm mixture over water bath
observation: shiny reflecting metallic silver
R-C(=O)H + 2Ag(NH₃)₂⁺ + 3OH^- > 2Ag + RC(=O)O^- + NH₃ + H₂O (redox reaction)

Fehling's solution
reagent: Fehling's solution (deep blue sol- contains Cu²⁺(aq) in alkaline sol)
[Fehling's solution: from Fehling's sol A (CuSO₄(aq)-blue sol) + Fehling's sol B (aq Na K tartrate + aq NaOH-colourless)]
condition: warm over water bath
observation: red ppt of Cu₂O formed (copper(I) oxide-red, copper(II) oxide-black)
R-C(=O)H + 2Cu²⁺ + 5OH^- > Cu₂O + R-C(=O)O^- + 3H₂O (redox reaction)

Oxidation
reagent: acidified oxidising agent: K₂Cr₂O₇/H⁺ or KMnO₄/H⁺
condition: heat under reflux
observation: excess aldehyde- K₂Cr₂O₇: orange > green (KMnO₄: purple > colourless)
R-C(=O)H + [O] >(KMnO₄, heat, reflux)> R-C(=O)OH

(ketones: resistant to oxidation > no reaction w/ Tollen's reagent, Fehling's sol or oxidising agent)


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