Carbonyl Compounds

Carbonyl Compounds
Aldehydes
Name
Methanal (Formaldehyde) Ethanal (Acetaldehyde) Propanal

Ketones
Name Structural Formula

Structural Formula
HCHO

CH3CHO CH3CH2CHO CH3CH2CH2CHO Propanone (Acetone) Butanone (CH3)2CO CH3COCH2CH3

Butanal

Glucose & Fructose (Simplest sugars)

Glucose (Chain Form)

Glucose (Ring Form)

Fructose (Chain Form) Fructose (Ring Form)

Naturally Occurring Carbonyls with Odours

Carvone

Typical odour of Heptan – 2- one

Almond Flavours

Spearmint

Caraway Seeds

Gen Properties
• General Formula: CnH2nO • Polarity:

• Miscibility: The polarity is sufficient to enable the lower members of the homologous series of Aldehydes and Ketones to be completely miscible with water. Water will form H- bonds to the carbonyl group.

Redox Reactions
1. Reduction: Aldehydes and ketones may be reduced to 10 alcohols and 20 alcohols, respectively using the reducing agent sodium tetrahydridoborate, NaBH4. (Water or ethanol is used as a solvent.) (a) Reduction of Ethanal CH3CHO + 2[H] NaBH4 in water CH3CH2OH (b) Reduction of Propanone CH3COCH3 + 2[H] NaBH4 in ethanol

CH3CH(OH)CH3

Regarded basically as the addition of H2 across the C=O double bond.

SAQ 19.4
• Draw the structural formulae for products obtained when the ff are treated with NaBH4: (i) Butanone (ii) Pentanal (iii) 2-Methylhexan-3-one

Redox Reactions
2. Oxidation:
Aldehydes require only mild conditions to oxidize to carboxylic acids CH3CHO + [O] K2Cr2O7/H+ CH3COOH
(reflux)

This reaction must be done with refluxing and not by distilling. Why….?

Addition of Hydrogen Cyanide
• Both Aldehydes and Ketones react with Hydrogen Cyanide to form a series of 2-Hydroxynitrile products with 1 more C. • Example 1:

Ethanal

2-Hydroxypropanenitrile

• Example 2:

Propanone

2-Hydroxy-2-methylpropanenitrile

The Mechanism…?
• Nucleophilic addition (check pg…. Of text book)