Organic Synthesis — Structured Questions (Cambridge International AS Chemistry): Exam Questions

Butan-1-ol can be converted directly into 1-bromobutane.

State the reagents and conditions required for this conversion.

Butan-1-ol is heated with concentrated sulfuric acid.

State the type of reaction involved and state the systematic name of the alkene formed.

Extract:

Butan-1-ol is heated with concentrated sulfuric acid.

State the type of reaction involved and state the systematic name of the alkene formed.

The type of reaction and the systematic name of the alkene formed are:

• Elimination / dehydration
• But-1-ene

The alkene formed in part (b) reacts with hydrogen bromide.

State the systematic name of the major organic product formed.

Describe one simple test-tube reaction that allows you to distinguish between compounds G and H shown in Fig. 2.1.

Fig. 2.1

Describe one simple test-tube reaction that allows you to distinguish between compounds I and J, shown in Fig. 2.2.

Fig. 2.2

Describe one simple test-tube reaction that allows you to distinguish between compounds K and L, shown in Fig. 2.3.

Fig. 2.3

A reaction pathway is shown in Fig. 3.1.

Fig. 3.1

State the reagents and conditions required for the conversion of:

i) compound A to compound B

ii) compound A to compound C

Extract:

A reaction pathway is shown in Fig. 3.1.

State the systematic name of compound C shown in Fig. 3.1 in part (a).

Extract:

A reaction pathway is shown in Fig. 3.1.

Compound A (1-bromopropane) converting to propene (compound B) via elimination, and to butanenitrile (compound C) via nucleophilic substitution

i) Compound B reacts with cold dilute acidified potassium manganate(VII) to form compound D. Draw the skeletal formula of compound D.

ii) Compound B also reacts with hot concentrated acidified potassium manganate(VII) to form compounds E and F. Draw the skeletal formulae of compounds E and F.

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

......................................................................................................................

equation

......................................................................................................................

Extract:

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.

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

intermediate

......................................................................................................................

step 1 reagents and conditions

......................................................................................................................

step 2 reagents and conditions

......................................................................................................................

Extract:

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.

The reagents, conditions and equation for the one-step process (hydration) are:

• Steam / water vapour / H₂O (g)
• Concentrated phosphoric acid / H₃PO₄ catalyst OR Concentrated sulfuric acid / H₂SO₄ catalyst
• CH₃CH=CHCH₃ + H₂O → CH₃CH(OH)CH₂CH₃

For the two-step process:

• Intermediate: 2-bromobutane
• Step 1 reagent: hydrogen bromide / HBr
• Step 2 reagent: aqueous sodium hydroxide / NaOH (aq) AND heat under reflux OR Aqueous potassium hydroxide / KOH (aq) AND heat under reflux

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

......................................................................................................................

conditions

......................................................................................................................

Extract:

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

{align=center} Fig. 2.1

Reaction scheme showing butan-1-ol converting to but-1-ene via reaction 1, to butanoic acid via reaction 2, and further reactions producing compounds U and V

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

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

Extract:

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

Fig. 2.1

Reaction scheme showing butan-1-ol converting to but-1-ene via reaction 1, to butanoic acid via reaction 2, and further reactions producing compounds U and V

Draw the structural formulae of compounds U and V.

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

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

Extract:

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 3.

reagent

......................................................................................................................

conditions

......................................................................................................................

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.

Extract:

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

Compound D is formed from compound A using cold dilute acidified KMnO4.

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

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

Extract:

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

(compound A is a molecule containing both a C=O and a C=C group)

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

......................................................................................................................

skeletal formula of organic ion

Extract:

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

Fig. 3.1 shows compound A (a molecule containing both a C=O and a C=C group) undergoing three reactions: LiAlH4 to give compound B, H2 with Ni catalyst to give compound C, and cold dilute acidified KMnO4 to give compound D

State the systematic name of compound A.

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

propene $\overset{\mathrm{reaction}1}{\rightarrow}$ propan-2-ol $\overset{\mathrm{reaction}2}{\rightarrow}$ compound G $\overset{\mathrm{reaction}3}{\rightarrow}$ 2-hydroxy-2-methylpropanenitrile

Name the mechanism for reaction 1 and reaction 3.

reaction 1

......................................................................................................................

reaction 3

......................................................................................................................

Extract:

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

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

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

reaction 1:

reaction 2:

Extract:

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

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

reaction 1, reaction 2, reaction 3

Reaction 3: nucleophilic addition

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.

Extract:

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

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

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

......................................................................................................................

type of reaction

......................................................................................................................

Extract:

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.

{align=center} Fig. 5.1

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.

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

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

......................................................................................................................

type of reaction

......................................................................................................................

Step 2 (intermediate to ethanol)

reagents and conditions

......................................................................................................................

type of reaction

......................................................................................................................

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.

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

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

compound D $\overset{\mathrm{step}1}{\rightarrow}$ compound E $\overset{\mathrm{HBr}}{\rightarrow}$ 1-bromo-1-methylcyclohexane

Fig. 1.1

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

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.

Extract:

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

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

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.

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

Extract:

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

compound D → (step 1) → compound E → (HBr) → 1-bromo-1-methylcyclohexane

Fig. 1.1

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

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

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

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

1-chlorobutane $\overset{\mathrm{Step}1}{\rightarrow}$ compound G -> from K _ 2 Cr _ 2 O _ 7 / H _ 2 SO _ 4 to Step 2 of compound H

Fig. 2.1

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

Extract:

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

1-chlorobutane → compound G → compound H (K₂Cr₂O₇/H₂SO₄)

Step 1: nucleophilic substitution Step 2: oxidation

In step 1, 1-chlorobutane reacts with NaOH (aq). The hydroxide ion is a nucleophile that displaces the chloride ion, forming butan-1-ol (compound G).

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.

Extract:

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

1-chlorobutane → compound G → compound H (K₂Cr₂O₇/H₂SO₄)

Step 1: nucleophilic substitution Step 2: oxidation

Step 2 is carried out by heating under reflux.

The systematic name of compound H is: Butanoic acid

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.

Extract:

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.

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

Extract:

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.

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.

Extract:

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.

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.