Nitriles & Hydroxynitriles — Structured Questions (Cambridge International A-Level Chemistry): Exam Questions

When 1-chloropropane is heated under reflux with ethanolic potassium cyanide, KCN, the following reaction occurs.

CH₃CH₂CH₂Cl + KCN → CH₃CH₂CH₂CN + KCl

i) Draw the displayed formula of the organic product formed in this reaction.

ii) State the systematic name of this organic product.

Extract:

When 1-chloropropane is heated under reflux with ethanolic potassium cyanide, KCN, the following reaction occurs.

CH3CH2CH2Cl + KCN → CH3CH2CH2CN + KCl

Suggest why this reaction is useful to chemists during the synthesis of other organic compounds.

The CH₃CH₂CH₂CN can undergo hydrolysis.

i) Construct an equation for the acid hydrolysis of CH₃CH₂CH₂CN.

ii) Draw the displayed formula of the intermediate formed when CH₃CH₂CH₂CN is hydrolysed by sodium hydroxide.

This question is about hydroxynitriles.

The hydroxynitrile shown in Fig. 2.1 can be prepared from the reaction between propanal and hydrogen cyanide.

Fig. 2.1

Give the systematic name of this hydroxynitrile.

Using 'curly arrows', complete the reaction mechanism shown in Fig. 2.2 for the reaction between propanal and the cyanide ion, CN^–.

Include any lone pairs of electrons and partial or whole charges.

Fig. 2.2

Extract:

Using 'curly arrows', complete the reaction mechanism shown in Fig. 2.2 for the reaction between propanal and the cyanide ion, CN⁻.

Name the type of reaction mechanism shown in Fig. 2.2.

Propanal undergoes nucleophilic addition with a mixture of HCN and NaCN to make 2-hydroxybutanenitrile, CH₃CH₂CH(OH)CN.

The mechanism for this reaction occurs in two main steps. The first step involves a nucleophile attacking the carbonyl carbon of propanal.

Explain which species acts as the nucleophile during this reaction.

Extract:

Propanal undergoes nucleophilic addition with a mixture of HCN and NaCN to make 2-hydroxybutanenitrile, CH3CH2CH(OH)CN.

The mechanism for this reaction occurs in two main steps. The first step involves a nucleophile attacking the carbonyl carbon of propanal.

The second step in the mechanism involves an intermediate species, CH₃CH₂C(O)HCN^–, reacting with HCN to form 2-hydroxybutanenitrile.

Draw the mechanism for this step.

• Identify the intermediate species that reacts with HCN.
• Include all charges, partial charges, lone pairs and curly arrows.

The structure of the 2-hydroxybutanenitrile product is shown in Fig. 1.1.

Fig. 1.1

Predict the values for the bond angles a and b shown in the diagram.

Extract:

Propanal undergoes nucleophilic addition with a mixture of HCN and NaCN to make 2-hydroxybutanenitrile, CH₃CH₂CH(OH)CN.

The product 2-hydroxybutanenitrile exists as a pair of stereoisomers.

i) Name the type of stereoisomerism shown by 2-hydroxybutanenitrile.

ii) Draw three-dimensional diagrams of this pair of stereoisomers. Indicate with an asterisk (*) the chiral centre on one of the structures drawn.

Two students try to prepare butanoic acid from a halogenoalkane in the laboratory.

Both students perform a nucleophilic substitution reaction to form P in reaction 1 of Fig. 2.1.

They both form butanoic acid from P but student A uses a single reaction, while student B uses two reactions.

Fig. 2.1

i) State the reagents and conditions required for reaction 1.

ii) Student A uses 1-bromopropane to form P.

Student B uses a different halogenoalkane which forms P at a slower rate.

Suggest the identity of the halogenoalkane that student B uses. Explain your answer.

Extract:

Two students try to prepare butanoic acid from a halogenoalkane in the laboratory.

Both students perform a nucleophilic substitution reaction to form P in reaction 1 of Fig. 2.1.

They both form butanoic acid from P but student A uses a single reaction, while student B uses two reactions.

Student A converts P into butanoic acid in a single step, reaction 2.

i) Name the type of reaction occurring in reaction 2.

ii) State an appropriate reagent for reaction 2 and name the other product of the reaction.

Extract:

Two students try to prepare butanoic acid from a halogenoalkane in the laboratory.

Both students perform a nucleophilic substitution reaction to form P in reaction 1 of Fig. 2.1.

They both form butanoic acid from P but student A uses a single reaction, while student B uses two reactions.

The reagents and conditions required for reaction 1 are:

• Heated under reflux
• With a solution of sodium cyanide / NaCN in ethanol OR With a solution of potassium cyanide / KCN in ethanol

Reaction 3 is alkaline hydrolysis and reaction 4 is acidification. Together, reactions 3 and 4 also produce butanoic acid.

Student B converts P into Q using dilute sodium hydroxide in reaction 3. This is followed by acidification of the product in reaction 4 to form butanoic acid.

Draw the structural formula of Q.

Extract:

Two students try to prepare butanoic acid from a halogenoalkane in the laboratory.

Both students perform a nucleophilic substitution reaction to form P in reaction 1 of Fig. 2.1.

They both form butanoic acid from P but student A uses a single reaction, while student B uses two reactions.

Explain why it is likely that student A will have a higher overall yield of butanoic acid from their halogenoalkane than student B.

Halogenoalkanes are often used as intermediates in organic reactions.

Three reactions of bromoethane, CH₃CH₂Br, are shown in Fig. 3.1.

Fig. 3.1

For each reaction, state the reagent and solvent used.

reaction 1

reagent ............................................................

solvent ............................................................

reaction 2

reagent ............................................................

solvent ............................................................

reaction 3

reagent ............................................................

solvent ............................................................

Extract:

Halogenoalkanes are often used as intermediates in organic reactions.

Three reactions of bromoethane, CH3CH2Br, are shown in Fig. 3.1.

Fig. 3.1

Reaction scheme showing three reactions of bromoethane: reaction 1 forming an alcohol with aqueous NaOH, reaction 2 forming an amine with ethanolic NH₃, reaction 3 forming a nitrile with ethanolic KCN

Reactions 1 and 3 require specific reaction conditions to occur as shown in Fig. 3.1.

For each reaction, give another solvent and the alternative product that will be formed.

reaction 1

alternative solvent ............................................................

alternative product............................................................

reaction 3

alternative solvent ............................................................

alternative product............................................................

Extract:

Halogenoalkanes are often used as intermediates in organic reactions.

Three reactions of bromoethane, CH3CH2Br, are shown in Fig. 3.1.

reaction 2 forming an amine with ethanolic NH₃

The product of reaction 2 can be converted into CH₃CN.

i) Name the compound CH₃CN.

ii) Name the type of reaction used to form CH₃CN.

Extract:

Halogenoalkanes are often used as intermediates in organic reactions.

Three reactions of bromoethane, CH3CH2Br, are shown in Fig. 3.1.

Reaction scheme showing three reactions of bromoethane: reaction 1 forming an alcohol with aqueous NaOH, reaction 2 forming an amine with ethanolic NH₃, reaction 3 forming a nitrile with ethanolic KCN

The product of reaction 3 can be used to produce propanoic acid by two different hydrolysis reactions.

Compare the two types of hydrolysis reaction in the production of propanoic acid from the product of reaction 3.

2-hydroxy-2-phenylpropanenitrile is shown in Fig. 1.1.

Fig. 1.1

Deduce the number of sigma (σ) and pi (π) bonds in 2-hydroxy-2-phenylpropanenitrile.

sigma ..............................

pi ..............................

Extract:

2-hydroxy-2-phenylpropanenitrile is shown in Fig. 1.1.

A molecule of 2-hydroxy-2-phenylpropanenitrile contains sp, sp² and sp³ hybridised carbon atoms.

State the number of sp, sp² and sp³ hybridised carbon atoms in a molecule of 2-hydroxy-2-phenylpropanenitrile.

Extract:

2-hydroxy-2-phenylpropanenitrile is shown in Fig. 1.1.

{align=center} Fig. 1.1

2-hydroxy-2-phenylpropanenitrile can be produced from compound X, a secondary alcohol, in a two-step synthesis.

compound X $\overset{\mathrm{step}1}{\rightarrow}$ compound Y $\overset{\mathrm{step}2}{\rightarrow}$ 2-hydroxy-2-phenylpropanenitrile

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

step 1

reagent ............................................................

conditions ............................................................

step 2

reagent ............................................................

conditions ............................................................

Extract:

2-hydroxy-2-phenylpropanenitrile is shown in Fig. 1.1.

2-hydroxy-2-phenylpropanenitrile can be produced from compound X, a secondary alcohol, in a two-step synthesis.

compound X → step 1 → compound Y → step 2 → 2-hydroxy-2-phenylpropanenitrile

i) Draw the mechanism for the second step in the synthesis of 2-hydroxy-2-phenylpropanenitrile.

You should clearly show the structure of compound Y and any intermediate formed and include all relevant charges, partial charges, curly arrows and lone pairs.

ii) Draw the structure of compound X.

2,2-dimethylpentanenitrile is useful in the synthesis of a variety of medicines and pharmaceuticals.

Draw the skeletal formula of 2,2-dimethylpentanenitrile.

2,2-dimethylpentanenitrile undergoes hydrolysis when heated with dilute hydrochloric acid.

Construct an equation for the hydrolysis of 2,2-dimethylpentanenitrile.

2,2-dimethylpentanoic acid can also be produced by the hydrolysis of 2,2-dimethylpentanenitrile using sodium hydroxide but this occurs in two steps.

i) Draw the fully displayed formula of the intermediate organic product.

ii) State the other product formed with this intermediate organic product.

iii) State the type of reaction that is required to produce 2,2-dimethylpentanoic acid from this intermediate organic product.