Esters (Cambridge (CIE) AS Chemistry): Exam Questions

Two isomeric compounds are shown below in Fig. 1.1.

Fig. 1.1

i) State the systematic name of each isomer.

[1]

ii) Suggest a chemical reagent to distinguish between these isomers and deduce the type of reaction taking place.

[2]

iii) State the observations made in each case.

[2]

i) Compound B, CH₃CH(CH₃)CH(OH)COOH, can be oxidised into compound C.

Construct an equation for this oxidation, using [O] to represent the oxidising agent.

[1]

ii) The half-equation for the reduction of acidified potassium dichromate(VI) is:

Cr₂O₇^2- (aq) + 14H⁺ (aq) + 6e^– → 2Cr³⁺ (aq) + 7H₂O (l)

Deduce the overall ionic equation for the oxidation of compound B to compound C using acidified dichromate(VI).

[2]

Acidified dichromate(VI) can be used to oxidise ethanol into ethanal or ethanoic acid, depending on the reaction conditions.

Outline how the reaction conditions can be changed to produce ethanal or ethanoic acid.

Under the right conditions, two molecules of compound A can react together to produce a dimer.

i) Name the type of reaction taking place and state the reaction conditions.

[2]

ii) Draw the structure of the product, showing clearly how the two molecules are joined.

[1]

An organic ester, B, has the empirical formula C₂H₄O. The relative molecular mass, M_r, of B is 88.0.

Deduce the molecular formula of B.

Draw the skeletal formulae of four isomers of B that are esters.

The student hydrolysed his sample of B by heating with aqueous mineral acid and then separating the alcohol, C, that was formed. He heated the alcohol C under reflux with acidified dichromate(VI) ions and collected the product D.

A sample of D gave a yellow/orange precipitate with 2,4-dinitrophenylhydrazine (2,4-DNP) reagent. A second sample of D gave no reaction with Tollens' reagent.

i) State the functional group shown to be present in D by the reaction with 2,4-DNP reagent.

[1]

ii) State what the result of the test with Tollens' reagent shows about D.

[1]

iii) Deduce the structural formula of the alcohol C.

[1]

iv) Which ester has the same structure as that of the ester B?

[1]

Which ester, if any, is chiral? Explain your answer.

The ester methyl butanoate, CH₃(CH₂)₂CO₂CH₃, contributes to the aroma of apples.

i) State the reagents and conditions needed for the hydrolysis of this ester.

[2]

ii) Construct an equation for the hydrolysis of this ester.

[1]

iii) Apart from their use as perfumes and food flavourings, state one major commercial use of esters.

[1]

Leaf alcohol has the structure shown below.

i) Draw the other stereoisomer of leaf alcohol.

[1]

ii) Draw the structure of the ester formed when leaf alcohol reacts with ethanoic acid. Show all bonds in the ester linkage.

[2]

i) Calculate the relative molecular mass, M_r, for leaf alcohol.

[1]

ii) Leaf alcohol was reacted to form a product with an M_r value 18 units less.

Suggest a structure for this product and deduce the type of reaction that took place.

[2]

Describe a simple chemical test to distinguish between leaf alcohol and your product in part (c)(ii).

State the reagent and the observation for each compound.

Ester S is 2-methylpropyl propanoate.

State the systematic names of the carboxylic acid and the alcohol used to form ester S.

State the catalyst and one condition for this reaction.

Construct an equation for the formation of ester S.

Draw the skeletal formulae of the organic products formed when ester S is:

i) heated under reflux with dilute aqueous sulfuric acid

[2]

ii) heated under reflux with aqueous sodium hydroxide

[2]

Ester T has the molecular formula C₅H₁₀O₂. When ester T is hydrolysed, one of the organic products is 2-methylpropan-1-ol.

Deduce the systematic names of the carboxylic acid and the alcohol used to prepare ester T.

Draw the displayed formula of ester T and state its systematic name.