Aldehydes and Ketones

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CARBONYL COMPOUNDS

- 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

Aldehydes

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

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

Isomers of C

3

H

7

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

2

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)

ketones

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

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