Aldehydes & Ketones (CIE AS Chemistry)

Calcium and its compounds have a large variety of applications.

Calcium metal reacts readily with most acids.

When calcium metal is placed in dilute sulfuric acid, it reacts vigorously at first.

After a short time, a layer of calcium sulfate forms on the calcium metal and the reaction stops. Some of the calcium metal and dilute sulfuric acid remain unreacted.

Suggest an explanation for these observations.

Calcium ethanedioate is formed when calcium reacts with ethanedioic acid, HOOCCOOH.

Calcium ethanedioate contains one cation and one anion.

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Calcium chlorate(I), Ca(ClO)₂, is used as an alternative to sodium chlorate(I), NaClO, in some household products.

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Deduce the oxidation number of chlorine in each species for the equation in (c)(ii).

Complete the boxes.

Calcium carbonate reacts with 2-hydroxypropanoic acid to form product Y.

Fig. 1.1

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Two possible methods of making 2-hydroxypropanoic acid are shown in Fig. 1.2.

Fig. 1.2

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Compound W can be converted into three different organic compounds as shown by the reaction scheme in Fig. 2.1.

Fig. 2.1

Write an equation for the formation of X. Use [H] to represent the reagent in the equation.

Identify the specific type of isomerism shown by the product Y, in Fig. 2.1. 

Draw the mechanism to show the formation Y and explain how this leads to the isomers of Y. 

When 5.00 cm³ of propanal (Mr = 58.0) were reacted with an excess of acidified potassium dichromate (VI) solution, 4.25 g of propanoic acid (Mr  = 74.0) were obtained.

The density of propanal is 0.810 g cm⁻³. 

Calculate the percentage yield for this reaction.

A different carbonyl compound, Q, (M_r = 72) reacts with 2,4-dinitrophenylhydrazine but not with Tollens’ reagent.

Q can be reduced to compound R. For this reaction

2-hydroxybutanoic acid can be made from propanal by via a reaction with hydrogen cyanide and the subsequent hydrolysis of 2-hyrdoxybutanenitrile. A possible pathway is shown in Fig. 3.1.The incomplete mechanism for reaction 2 is shown in Fig. 3.2. 

Fig. 3.1

Fig. 3.2

2-hydroxybutanenitrile contains a chiral centre. Draw the three-dimensional structures of the two optical isomers.

State the reagent(s) for reaction 3.

Compound A forms propanal when reacted with acidified potassium dichromate. Give the structural formula of compound A. 

Compound A and propanal were tested using a series of reagents outlined in Table 3.1. For each of the tests listed: 

• State the positive result
• Identify which compound(s) would give a positive result

Table 3.1 

Aqueous sodium tetrahydridoborate, NaBH₄, is a common reducing agent.

Identify two isomers with the formula C₃H₆O that cannot be reduced by aqueous NaBH₄.

Identify the two isomers with the formula C₃H₆O that can be reduced by aqueous NaBH₄.

When NaBH₄ is used as a reducing agent followed by the addition of acid, the reduction products of ketones can exhibit optical isomerism, while the reduction products of aldehydes cannot.

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Explain why the reduction product of a carbonyl compound, by NaBH₄ and acid, cannot be a tertiary alcohol.

This question is about the reactions of an organic compound R.

Analysis of 15.0 g of an organic compound, R, showed it to contain 69.8% carbon, 2.79 g of oxygen and the remaining mass was hydrogen.

Compound R is a straight chain organic compound. One isomer of compound R produces optical isomers of compound S when reacted with hydrogen cyanide followed by dilute acid.

Compounds R and S were tested with acidified potassium dichromate(VI) and Tollens reagent. The results are shown in Table 2.1.

Table 2.1

Using this information and your answer from part (a), identify compounds R and S.
Justify your answer.

Draw 3D representations of the two optical isomers of compound S.

There are some isomers of compound S that do not display optical isomerism.

Draw the skeletal formula of these isomers.