Aldehydes and Ketones



- Aldehydes and Ketones

• Structure

• carbonyl groups consists of a carbon-oxygen double bond

• the bond is polar due to the difference in electronegativity

aldehydes and ketones differ in what is attached to the carbon.

• ALDEHYDES - at least one H attached

• KETONES - two carbons attached


• Functional group: CHO, and is always at the end.

• Replace the “e” of the alkane with “ al ”

• Isomers of C




CHO (x2)

• C=O strongly polar

• No hydrogen bonding, high boiling point

• • substituent's are numbered based on the C with the O being number 1

Preparation of ethanal

• Chemicals: ethanol and sodium dichromate

• Word equation: ethanol + sodium dichromate

= ethanal + water

• Chemical equation:

• Sodium dichromate is an oxidising agent.

• Cr(+6) + 3e = Cr(+3)

• Orange green

• Alcohol is in excess to prevent further oxidation to the acid.

• Ice around the collecting flask to cool the ethanal as it has a low boiling point.

• Set up is for distillation.

Reactions of ethanal

• Fehlings 1 and 2: royal blue to red brick precipitate.

• Cu


O formed

• Cu(+2) + e = Cu(+1)

• Blue red

• Ammoniacal silver nitrate(Tollen’s reagent)

• Warmed

• Ethanal oxidised to ethanoic acid

• Ag(+) + e = Ag

• Aldehydes reduced the silver/ ketones don’t

• Acidified potassium permanganate:

• Purple to colourless

• Mn(+7) oxidised to Mn(+2)


• The carbon with the C = O must be attached to two other carbons.

remove E from the equivalent alkane name and add ONE

• if necessary, the position of the C=O is given

(lower number counting from one end)

• Draw up to 4 carbons and name