Organic Synthesis (Cambridge (CIE) AS Chemistry): Exam Questions

But-2-ene can be converted into butan-2-ol by two different synthetic routes. One route is a one-step process and the other is a two-step process.

State the reagents and conditions required for the one-step process. Construct an equation for this reaction using structural formulae.

reagents and conditions

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equation

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For the two-step process, identify the intermediate organic compound and state the reagents and conditions required for each step.

intermediate

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step 1 reagents and conditions

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step 2 reagents and conditions

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But-1-ene can also be used to form butan-2-ol by both the one-step and two-step reaction routes.

Explain why using but-1-ene gives a lower yield of butan-2-ol compared to using but-2-ene.

Draw the fully displayed formula of the organic product(s) formed when but-2-ene is:

• reacted with cold dilute acidified KMnO₄

• reacted with hot concentrated acidified KMnO₄

A series of reactions based on butan-1-ol is shown in Fig. 2.1.

Fig. 2.1

State the reagent and conditions required for reaction 1.

reagent

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conditions

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i) Construct an equation for reaction 2. Use [O] to represent one atom of oxygen from an oxidising agent.

[1]

ii) State the reagents and conditions required for reaction 2.

[2]

Draw the structural formulae of compounds U and V.

U ......................................................................................................................

V ......................................................................................................................

State the reagent and conditions required for reaction 3.

reagent

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conditions

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Some reactions of compound A are shown in Fig. 3.1.

Fig. 3.1

Draw the skeletal formulae of compounds B, C and D in the table below.

State the colour change observed during the reaction to form compound D.

from ....................................... to .......................................

Compound A reacts with alkaline I₂ (aq) to form a yellow precipitate and an organic ion.

Identify the yellow precipitate and draw the skeletal formula of the organic ion.

identity of yellow precipitate

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skeletal formula of organic ion

State the systematic name of compound A.

The reaction scheme shows three steps to synthesise 2-hydroxy-2-methylpropanenitrile.

propene propan-2-ol compound G 2-hydroxy-2-methylpropanenitrile

Name the mechanism for reaction 1 and reaction 3.

reaction 1

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reaction 3

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State the reagents and conditions required for reaction 1 and reaction 2.

reaction 1:

reaction 2:

Complete the diagram to show the mechanism for reaction 3. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. Draw the structure of the organic intermediate.

Explain why 2-hydroxy-2-methylpropanenitrile does not exhibit optical isomerism.

The following reaction pathway in Fig. 5.1 is used to produce compounds A and B, which when reacted together, form a branched ester molecule, compound C.

State the reagents and conditions for the synthesis of compound A via step 1 and state the type of reaction.

Fig. 5.1

reagents and conditions

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type of reaction

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In order for the ester to be produced, the ketone shown in Fig. 5.1 must be converted to another compound, B.

i) State the systematic name and draw the fully displayed formula of compound B that is produced from step 2.

[2]

ii) State the type of reaction involved in step 2 and state the reagents and conditions required.

[2]

Outline how ethanol can be synthesised from ethane in two steps. State the reagents, conditions and type of reaction for each step.

Step 1 (ethane to intermediate)

reagents and conditions

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type of reaction

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Step 2 (intermediate to ethanol)

reagents and conditions

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type of reaction

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The four-step synthesis shown in Fig. 5.2 produces propan-1-ol from a ketone.

Fig. 5.2

i) State the systematic name of compound D.

[1]

ii) State the reagents and conditions required for step 4.

[2]

1-bromo-1-methylcyclohexane can be produced by the following reaction steps, as shown in Fig. 1.1.

compound D compound E 1-bromo-1-methylcyclohexane

Fig. 1.1

i) Name the mechanism for the reaction between compound E and hydrogen bromide.

[1]

ii) Complete the diagram to show the mechanism for this reaction. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. Draw the structures of the organic intermediate and the major organic product.

[4]

Explain why a major product and a minor product are produced in the reaction outlined in part (a).

Compound E can be synthesised from compound D in step 1.

i) Draw the skeletal formula of a possible structure for compound D.

[1]

ii) State the reagents and conditions required for step 1, based on your suggested structure for compound D.

[2]

A reaction scheme starting from 1-chlorobutane is shown in Fig. 2.1.

1-chlorobutane compound G compound H

Fig. 2.1

State the type of reaction for each of step 1 and step 2.

Step 2 is carried out by heating under reflux.

State the systematic name of compound H.

1-chlorobutane can be produced as the minor product when an unbranched alkene reacts with hydrogen chloride.

Draw the skeletal formula of this alkene and state the reagent required.

2-chlorobutane can be used instead of 1-chlorobutane as the starting compound in the reaction scheme in Fig. 2.1.

Identify the homologous series of the final organic compound formed and explain why this is different from compound H.

Compounds W, X, Y and Z contain carbon, hydrogen and oxygen only. Compounds X and Y are unbranched molecules, each containing five carbon atoms. X reacts with Y in the presence of an acid catalyst to form W and a by-product, Z. X can be oxidised by heating with acidified potassium dichromate(VI) to give Y.

2.754 g of compound Y contains 0.0270 mol.

Calculate the relative molecular mass of compound Y and use this to state its systematic name.

Draw the structural formula of compound W and identify by-product Z.

By altering the reaction conditions, the oxidation of compound X can be stopped before compound Y is produced.

Identify the homologous series of the organic compound produced at this intermediate stage and state the conditions required to favour its formation.

Draw the skeletal formula of a structural isomer of compound X that does not react with acidified potassium dichromate(VI), H⁺/K₂Cr₂O₇, and state its systematic name.