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C26.1 Introduction to aldehydes and ketones AQA A2 Compount Containing Carbonyl Groups: Page No. 157
1:
a Pentan-3-one
b Propanal
2
A ketone must have a C= O group with two carbon-containing groups attached to it, so at least three carbon atoms are required.
The C=O group can only be on carbon 2, otherwise the compound would be an aldehyde.
c The C=O group must always be on the end of the chain.
3 A hydrogen bond requires a molecule with a hydrogen atom covalemly bonded to an atom of fluorine, oxygen, or nitrogen. There is no such carbon atom in propanone.
4 The hydrogen atom in a.n -OH group in a water molecule can hydrogen bond with the oxygen atom in the C=O bond of propanone.
26.2 Reactions of the carbonyl group in aldehydes and ketonesAQA A2 Compount Containing Carbonyl Groups: Page No. 160
1 w, cr, Cl •
Cl
–
2 a
No
b A negatively charged nucleophile will be repelled by the high electron density in the C= C.
c
3
4 The cN-ions can at.tack the planar C= O group from above or below. In the case of CHCHO this will produce a compound with a chiral centre (four different groups attached to it). This will be a pair of optical isomers. As attack from above or below is equally likely it will be a 50:50 mixture (racemic). In the case of CH
3COCH3′ the product will not have a carbon atom with four groups attached to it. It will not therefore be chiral and will be a single compound.
26.3 Carboxylic acids and esters AQA A2 Compount Containing Carbonyl Groups : Page No. 163
1
3-brornobutanoic acid
2
3 The carboxylic acid must be at the end of a chain and therefore in the 1 position.
4
Ethyl ethanoate; methyl propanoate
26.4 Reactions of carboxylic acids and esters AQA A2 Compount Containing Carbonyl Groups: Page No. 167
- They react with carbonates and hydrogencarbonates to give carbon dioxide, metal oxides to give salts, and alkalis to give salts.
2 Methanol and ethanoic add
3 Ethanol and methanoic acid
4 They have the same molecular formula but have a different arrangement of their atoms in space.
26.5 Acylation AQA A2 Compount Containing Carbonyl Groups: Page No. 172
1 The carbon of the C= O group is strongly cO+ because, as well as oxygen, it is also bonded to an electronegative chlorine atom whid1 draws electrons away from it.
2
OH-, because it is negatively charged and contains a lone pair of electrons.
3
Because the nucleophile and the acylating agent join together and then a small molecule is lost.
4
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Practice questions: Page No. 173
1 (a) CH
3OH + CH
3CH
2COOH → CH
3CH
2COOCH
3 + H
2O
(b) Nucleophilic addition–elimination
(c)
(d) (i) A selection of answers are correct here. These are : faster/ not reversible/ bigger yield /purer product/ no acid catalyst required
(ii) Anhydride less easily hydrolysed or reaction less exothermic.
2
(a) Nucleophilic addition
(b) (i) Name compound Q.
2-hydroxybutanenitrile
(ii)
(c) (i) methanol in the presence of a few drops of concentrated sulfuric acid;
(ii)
(iii) CH
3CH=CHCOOH
3 (a) (Nucleophilic) addition – elimination;
(b)
4
(a)
Propan(e)-1,2,3-triol
(b)
CH
3(CH
2)
16COONa
or C
17H
35COONa
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References:
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