Nucleophilic addition

This question is about carbonyl compounds.

The three compounds below each contain a ketone and one other functional group.

Pyruvic acid
Methylglyoxal
Acetol

What is a functional group ?

A chemical test is carried out which gives a positive result for all three compounds.

Suggest the reagent and observation of this chemical test.

Reagent........

Observation........

A student is provided with three unlabelled sample tubes, containing either pyruvic acid, methylglyoxal or acetol.

The student carries out three chemical tests on each sample.

Complete the table with the expected observations, including ‘no change’ where appropriate.

Complete the flowchart for the reactions of pyruvic acid.

This question is about two metal hydrides, lithium aluminium hydride, LiAl H₄, and sodium borohydride, NaBH₄. Both hydrides are used as reducing agents in organic chemistry.

What is the systematic name of the alcohol C₆H₅CH₂OH?

Calculate the mass of LiAl H₄ that the student should use in Step 2 and the percentage yield of pure C₆H₅CH₂OH obtained in Step 4.

Give the mass of LiAl H₄ and the percentage yield of pure C₆H₅CH₂OH to 3 significant figures.

Percentage yield of pure C₆H₅CH₂OH =........ %

In the preparation, LiAl H₄ behaves as a nucleophile.

What is meant by the term nucleophile ?

The mechanism for Step 2 in the reduction of C₆H₅COOC₂H₅ is shown below. In the mechanism, LiAl H₄ can be represented as H^–.

Complete the mechanism by adding curly arrows to the three boxes.

Suggest why the student heated the mixture from Step 2 with dilute aqueous acid in Step 3.

NaBH₄ contains Na⁺ and BH₄^– ions.

Draw a ‘dot‑and‑cross’ diagram for NaBH₄.

Use a different symbol for the electrons from each element.

Show outer electrons only.

NaBH₄/ O₂ cells are being investigated as potential fuel cells.

• The positive electrode contains O₂.

• The negative electrode contains NaBH₄.

The reaction at the positive electrode and the overall cell reaction for a NaBH₄/ O₂ fuel cell are shown below.

Overall cell reaction: NaBH₄ + 2O₂ NaBO₂ + 2H₂O E = 1.64 V

What is the standard electrode potential of the negative electrode in this cell?

Construct the equation for the reaction at the negative electrode of this cell.

19* Alkenes and carbonyl compounds take part in addition reactions.

Describe one addition reaction of an alkene and one addition reaction of a carbonyl compound.

Include reagents and reaction mechanisms.

This question is about reactions of acrolein, H₂C=CHCHO.

Acrolein reacts with sodium cyanide in acidic conditions, NaCN(aq) / H + (aq).

Outline the reaction mechanism for this reaction, showing the intermediate and the organic product.

The structure of acrolein has been provided.

Include curly arrows and relevant dipoles.

Name this type of mechanism.

This question is about compounds that contain the carboxylic acid functional group.

Carboxylic acids react with alkalis, metals and carbonates to form salts.

Write full equations for the following three reactions. Show structures for organic compounds.

• the reaction of propanoic acid with aqueous potassium hydroxide:

• the reaction of aqueous methanoic acid with magnesium:

• the reaction of the –amino acid, aspartic acid (R=CH₂COOH), with an excess of aqueous sodium carbonate, Na₂CO₃:

This part is about polymers derived from carboxylic acid monomers.

Poly(pent-3-enoic acid) is an addition polymer.

Draw the structure of pent-3-enoic acid and two repeat units of this polymer.

Butanedicarboxylic acid and 1,4-dihydroxy-2-methylbenzene react to form a condensation polymer.

Draw one repeat unit of this condensation polymer.

Three repeat units of a condensation polymer are shown below.

Draw the structure of the monomer required to form this polymer.

A polymer is formed from 400 molecules of 2-aminopropanoic acid.

Draw one repeat unit of this polymer.

What is the relative molecular mass, M_r, of the polymer?

Which reaction is not a reduction?

This question is about organic synthesis.

Prenal, shown below, is used in the synthesis of some pharmaceuticals.

What is the systematic name for prenal?

* A student intends to synthesise compound A using the two-stage route below.

(chloromethyl)benzene Compound A

Plan a two-stage synthesis to prepare 5.44 g of compound A starting from (chloromethyl)benzene, C₆H₅CH₂Cl. Assume that the overall percentage yield of compound A from (chloromethyl)benzene is 25%.

In your answer, include the mass of C₆H₅CH₂Cl required, reagents, and equations where appropriate.

Purification details are not required.

The carbonyl compounds, F and G, shown below, contribute to the flavour of coffee.

Compound F is a member of a homologous series.

Explain the term homologous series.

Predict the molecular formula for the member of this homologous series containing 24 carbon atoms.

Describe suitable chemical tests, with observations, that would confirm the presence of the functional groups in F and G.

Explain why the mechanism in (c)(i) involves heterolytic fission.

This question is about organic compounds containing nitrogen.

Salt H, (CH₃)₂CHNH₃Cl, is used in the manufacture of garden weedkillers.

The flowchart shows the synthesis of the salt H from propanone.

Complete the flowchart. Show structures for organic compounds.

Aspartame, shown below, is an artificial sweetener commonly used as a sugar substitute.

Aspartame contains several functional groups.

Apart from the benzene ring, name the functional groups in aspartame.

A sample of aspartame is hydrolysed with aqueous acid.

Draw the structures of the three organic products of the complete acid hydrolysis aspartame.

A carbonyl compound is reacted with NaBH₄.

Which compound(s) could be formed?

1 2-Methylpentan-2-ol

2 2-Methylpentan-1-ol

3 3-Methylpentan-2-ol

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

This question is about benzene.

Over time, the Kekulé and delocalised models have been used to describe the bonding and structure of a benzene molecule.

Describe, in terms of orbital overlap, the similarities and differences between the bonding in the Kekulé model and the delocalised model of benzene.

Experimental evidence led to the general acceptance of the delocalised model over the Kekulé model.

Describe two pieces of evidence to support the delocalised model of benzene.

Benzene can be used as the starting material for the synthesis of compounds D and E, shown below.

In the diagrams C₆H₅ is a phenyl group.

Compounds D and E can be converted into polymers.

Draw two repeat units of these polymers.

Two repeat units of polymer formed from D

Two repeat units of polymer formed from E

State the type of polymer formed from compounds D and E.

From compound D........

From compound E........

In the synthesis of compounds D and E, benzene is first reacted with ethanoyl chloride, CH₃COCl, to form phenylethanone, shown below.

The reaction takes place in the presence of aluminium chloride, Al Cl₃, which acts as a catalyst.

In the mechanism for this reaction,

• ethanoyl chloride first reacts with aluminium chloride to form the CH₃–C⁺=O cation

• the CH₃–C⁺=O cation then behaves as an electrophile.

Complete the mechanism for the reaction.

Include equations to show the role of the Al Cl₃ catalyst, relevant curly arrows and the structure of the intermediate.

Formation of electrophile........

Regeneration of catalyst........

Complete the flowchart for the synthesis of compounds D and E from phenylethanone.

Cinnamaldehyde and methylcinnamaldehyde are naturally occurring organic compounds.

Methylcinnamaldehyde is an E stereoisomer.

Explain this statement in terms of the Cahn-Ingold-Prelog (CIP) rules.

A student plans to carry out some chemical tests on both cinnamaldehyde and methylcinnamaldehyde.

Suggest a suitable chemical test to confirm that both compounds contain an unsaturated carbon chain.

Your answer should include the reagent and observations.

Describe a chemical test to confirm that both compounds contain an aldehyde functional group.

Your answer should include the reagent and observations.

Describe a chemical test to confirm that cinnamaldehyde and methylcinnamaldehyde contain a carbonyl group.

How could the products of this test be used to distinguish between the two compounds?

Your answer should not include spectroscopy.

This question is about alcohols.

Construct an equation for the complete combustion of an unsaturated alcohol with 5 carbon atoms.

Many alcohols, including ethanol, are soluble in water.

Explain, with the aid of a diagram, why ethanol is soluble in water.

Include relevant dipoles and lone pairs.

The solubility of hexan-1-ol and hexane-1,6-diol in water is shown below in Table 19.1

Explain the difference in solubility of hexan-1-ol and hexane-1,6-diol.

Alcohols are important in organic synthesis and can be formed by the reduction of carbonyl compounds.

Complete the flowchart by filling in each box.

What is the name of compound K ?

Butan-1-ol can be oxidised to form two different organic products, depending on the reaction conditions used.

Describe both oxidation reactions of butan-1-ol.

For each reaction include

• the structure of the organic product

• a balanced equation

• the essential reaction conditions.

In your equations you may use [O] to represent the oxidising agent.