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. C3H6O  C2H5COOH   (d) Name the compound with the formula C2H5COOH. (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) C3H6O + H2O  C2H5COOH + 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. 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 CH3 O CH3 - C CH3 - C - C H H H Name alkene X in this reaction. +O2 (a) Y and Z are both aldehydes. (b) 4-methylpent-2-ene

4. Propan-2-ol can be prepared from propane as follows. CH3 —CH2—CH3 CH3 —CH = CH2 CH3 —CH—CH3 O H condensation cracking dehydration hydration hydrolysis oxidation (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 1 Step 2 Cracking. 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 Carbonyl group. 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. Oxidation. 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.

7. Glucose is produced in plants by photosynthesis. (a) Plants convert glucose into a condensation polymer for storing energy. Name the condensation polymer. (b) One way of representing the structure of glucose in aqueous solution is shown below.   In this structure the aldehyde group is circled. What would be seen when glucose is oxidised using Tollen’s reagent? Complete the structure below to show the product formed when glucose is oxidised.  Starch. (b) (i) A deposit of shiny, silver coloured metal – silver would appear on the side of the test tube. (ii) See diagram above. O -O-H

8. . The structures of two antiseptics are shown. Both are aromatic.   TCP phenol (a) (i) What gives the aromatic ring its stability? (ii) Write the molecular formula for TCP. (iii) The systematic name for TCP is 2,4,6-trichlorophenol The systematic name for Dettol, another antiseptic, is 4-chloro-3,5-dimethylphenol. Draw the structural formula for Dettol. The feedstocks for the production of antiseptics are made by reforming the naphtha fraction of crude oil. Give another use for reformed naphtha. (a) (i) Delocalised electron ring. (ii) C6H3Cl3O. (iii) (b) Petrol.

9. Compound X is secondary alcohol.   compound X (a) Name compound X. (b) Draw the structural formula for the tertiary alcohol that is an isomer of compound X. (c) When passed over heated aluminium oxide, compound X is dehydrated, producing isomeric compounds Y and Z. Both compounds Y and Z react with hydrogen bromide, HBr. Compound Y reacts to produce two products while compound Z reacts to produce only one product. compound Y 2 products compound Z 1 product Name compound Z. HBr HBr Butan-2-ol (b) CH3 CH3 - C – O – H CH3 (c) But-2-ene.