HIGHER CHEMISTRY REVISION. Unit 2:- Reactions of Carbon Compounds 1. Although aldehydes and ketones have different structures, they both contain the carbonyl functional group. (a) In what way is the structure of an aldehyde different from that of a ketone? (b) As a result of the difference in structure, aldehydes react with Fehling’s (or Benedict’s) solution and Tollen’s reagent but ketones do not. What colour change would be observed when propanal is heated with Fehling’s (or Benedict’s) solution? (c) In the reaction of propanal with Tollen’s reagent, silver ions are reduced to form silver metal. Complete the following ion-electron equation for the oxidation. C 3 H 6 O  C 2 H 5 COOH (d) Name the compound with the formula C 2 H 5 COOH. (a) The carbonyl group is on the end of the carbon chain in the aldehyde. It is not on the end of the carbon chain in a ketone. (b) Colour changes from Blue to orange-red. (c) C 3 H 6 O+ H 2 O  C 2 H 5 COOH + 2H + + 2e - (d) Propanoic acid

2. As a result of both containing the carbonyl group, aldehydes and ketones react in a similar way with hydrogen cyanide. The equation for the reaction of propanal with hydrogen cyanide is shown. (i) Suggest a name for this type of reaction. (ii) Draw a structure for the product of the reaction between propanone and hydrogen cyanide. (a) Addition. (b) H H O H H –C - C - C-H H CN H

3. Alkenes can react to produce unstable compounds called peroxides. These peroxides break down rapidly to form compounds which have the same functional groups. For example, alkene X reacts to produce compounds Y and Z. (In the following structural formula R’ and R’’ are used to represent different alkyl groups). O R’ - C H Compound Y H H H H R’ - C = C - R’’  R’ - C - C - R’’  + alkene X O O O peroxide R’’ - C H Compound Z (a ) To which homologous series do both compounds Y and Z belong? (b) In one reaction, alkene X reacts to produce the two compounds shown below. O CH 3 O CH 3 - C CH 3 - C - C H H H Name alkene X in this reaction. +O 2 (a) Y and Z are both aldehydes. (b) 4-methylpent-2-ene

4. Propan-2-ol can be prepared from propane as follows. CH 3 —CH 2 —CH 3 CH 3 —CH = CH 2 CH 3 —CH—CH 3 O H condensation crackingdehydration hydration hydrolysisoxidation (a) Identify the name of the type of reaction taking place at Step 1. (b) Identify the name of the type of reaction taking place at Step 2. Step 1Step 2 (a)Cracking. (b)Hydration

5. Propanone and propanal both contain the same functional group. (a) Name this functional group. (b) This diagram show how to distinguish between propanone and propanal. Explain what is observed in the reaction between propanal and Tollen’s reagent. Tollens Reagent (a)Carbonyl group. (b)A silver mirror forms on the side of the test tube. The silver ions in the Tollen’s reagent are reduced to silver atoms. Ag + (aq) + e -  Ag(s) The propanal is oxidised to propanoic acid.

6. Peeled apples turn brown due to reactions of compounds called phenols. The first two steps in the reaction of one phenol, A, are :- (a) The same type of reaction takes place in both steps. Give the name of this type of reaction. (b) The molecular formula for compound A can be written as C7HxO. What is the value of x? (c) An enzyme called phenolase, present in apples, acts as a catalyst during the browning of apples. It has been discovered that covering a slice of apple with lemon juice stops it from going brown. Suggest a reason for this. (a)Oxidation. (b)X = 8 (c) The acid changes the pH conditions which denatures the enzyme so that it no longer acts as a catalyst. When an enzyme is denatured its shape is changed irreversibly.