Electrophilic addition

Ethene can be reacted with hydrogen bromide.

Which statement about this reaction is correct?

A H – acts as a nucleophile.

B Br + acts as an electrophile.

C H⁺— Br^– acts as an electrophile.

D H⁺— Br^– acts as a nucleophile.

This question is about hydrocarbons with six carbon atoms.

Compound A is a hydrocarbon:

Compound A

What is the systematic name of compound A ?

The table below shows incomplete information about two hydrocarbons.

Complete the table.

Compound B, CH₃CH=C(CH₃)CH₂CH₃, exists as E and Z stereoisomers.

Draw the structures of the E and Z stereoisomers of compound B.

Explain why compound B can form E and Z stereoisomers.

Hexane, C₆H₁₄, is used as a fuel.

1.0 mol of hexane is mixed with 6.0 mol of oxygen and combusted.

Construct an equation for the incomplete combustion of 1.0 mol of hexane with 6.0 mol of oxygen.

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 aromatic compounds.

Ethylbenzene, C₆H₅CH₂CH₃, can be prepared by reacting benzene with chloroethane, CH₃CH₂Cl, in the presence of Al Cl₃. The Al Cl₃ acts as a halogen carrier.

Ethylbenzene

In the mechanism, chloroethane reacts with the halogen carrier to form a carbocation, which acts as the electrophile.

What is meant by the term electrophile ?

Outline the mechanism for this reaction, including the role of Al Cl₃ as a halogen carrier.

The table shows directing effects for different groups in the electrophilic substitution of aromatic compounds.

The reactions of C₆H₅NH₂ are similar to the reactions of phenol.

Write an equation for the tri-substitution of C₆H₅NH₂ with chlorine.

Explain why chlorine reacts much more readily with C₆H₅NH₂ than with benzene.

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 unsaturated hydrocarbons.

What is the systematic name of hydrocarbon A ?

Compounds B and C are branched hydrocarbons that are structural isomers of C₆H₁₂.

Compounds B and C both have stereoisomers.

• Compound B has cis and trans isomers but does not have optical isomers.

• Compound C has optical isomers but does not have cis and trans isomers.

What is meant by the term structural isomers ?

What is meant by the term stereoisomers ?

Draw structures for the cis and trans isomers of the branched hydrocarbon B.

Draw 3D structures for the optical isomers of compound C.

Compounds D and E are two more structural isomers of C₆H₁₂.

Compounds D and E do not show stereoisomerism.

Table 16.1 shows NMR and infrared (IR) spectral data for D and E.

Draw the structures of D and E and explain how the spectral data in Table 16.1 provides evidence for the structures.

Draw the structures of the products you would expect from the ozonolysis of the two compounds below.

This question is about the chemistry of aromatic compounds.

What chemical test(s) could be used to confirm the presence of the phenol group in compounds K and L ?

A student thought that¹³C NMR spectroscopy could be used to distinguish between compounds J, K and L.

Explain, with reasoning, whether the student is correct.

Compound J is substituted at the 2-and 4-positions by chlorine in the presence of a catalyst.

Outline the mechanism for the 4 substitution of compound J by chlorine in the presence of a catalyst.

Show the role of the catalyst.

Compounds K and L react with chlorine much more readily than compound J.

Explain why.

Compound J, C₆H₅CH₂CH₂OH, is reacted with acidified potassium dichromate(VI) under reflux to form organic product M.

Write an equation for this reaction.

Use [O] to represent the oxidising agent and show the structure of M.

A two-stage synthesis of an amine from compound J is shown below.

Add the reagents for each stage of this synthesis.

Compound J

But-1-ene, H₂C=CHCH₂CH₃, and buta-1,3-diene, H₂C=CH–CH=CH₂, are unsaturated compounds used to make many organic products.

But-1-ene and buta-1,3-diene have -bonds and -bonds.

How many - and -bonds are in one molecule of buta-1,3-diene?

-bonds:........ -bonds:........

But-1-ene is reacted with hydrogen bromide, forming a mixture of two saturated organic products.

One of the organic products is formed in a much greater quantity than the other organic product.

Explain why one organic product is formed in a much greater quantity than the other organic product.

Buta-1,3-diene is reacted with an excess of hydrogen bromide, forming a mixture of saturated organic products.

How many saturated organic products could be present in this mixture?

A student thought that buta-1,3-diene can show stereoisomerism.

The student drew out skeletal formulae for the stereoisomers of buta-1,3-diene:

Explain the term stereoisomerism.

Explain, with a reason, whether the student is correct or incorrect.

‘Diels-Alder’ reactions are used in the synthesis of many important organic compounds.

The Diels-Alder reaction of buta-1,3-diene with ethene is shown below.

Add curly arrows to the diagram below to complete the mechanism for this Diels-Alder reaction.

Two more Diels-Alder reactions of buta-1,3-diene are shown below.

In the boxes, draw the organic product of each reaction.

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.

Compounds B and C, shown below, are unsaturated hydrocarbons containing nine carbon atoms.

Compound B reacts with chlorine at room temperature, but compound C requires the presence of a halogen carrier.

In both reactions, the organic compound reacts with chlorine in a 1:1 molar ratio.

Draw the structures of the organic product of each reaction.

Outline the mechanism for the reaction of compound C with chlorine.

Show the role of the halogen carrier.

Compound C can be prepared by ‘trimerisation’ of propanone using concentrated sulfuric acid as a catalyst.

Suggest an equation for this reaction, using molecular formulae.

An organic chemist is investigating compound D for possible use as a medicine.

The chemist proposes a synthesis of compound D from compound C.

The chemist develops a three-stage synthesis of compound D from compound C.

Complete the flowchart. Show structures for organic compounds.

This question is about unsaturated aldehydes and alcohols.

Outline the reaction mechanism for the formation of one of the organic products.

Include curly arrows and relevant dipoles.

Explain why one of the organic products forms in a much greater quantity than the other organic product.

Describe how the observations from a chemical test would distinguish between geraniol and citronellal.

What is the molecular formula of geraniol?

Explain why geraniol and citronellal are structural isomers of each other.

Explain the term stereoisomerism.

This question is about reactions of organic compounds containing carbon, hydrogen and oxygen.

A chemist investigates two reactions of alcohol A, shown below.

What is the systematic name of alcohol A ?

What is the structural formula of alcohol A ?

The chemist heats alcohol A with an acid catalyst to form a mixture containing alkenes.

Draw the structures of the two alkenes formed in this reaction.

The chemist heats alcohol A with sodium chloride and sulfuric acid.

Construct a balanced equation for this reaction. Show structures for the organic compounds in your equation.

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 organic reactions.

Give the systematic name for compound A.

What type of reaction has taken place?

A similar reaction takes place when propanone, (CH₃)₂CO, is mixed with OH^–(aq) ions.

Draw the structure of the organic product of this reaction.

* Many organic reactions use electrophiles as reagents.

Explain the role of electrophiles in organic chemistry.

Your answer should include one reaction of an aliphatic compound and one reaction of an

aromatic compound, including relevant mechanisms.

This question is about unsaturated hydrocarbons.

Compound A and compound B are isomers.

Compound A has a lower melting point than compound B.

Suggest why.

Compound C, CH₃CH₂CH=CHCH₂CH₂OH, exists as cis and trans stereoisomers.

Name compound C.

Define the term stereoisomers.

Draw the structures of the cis and trans stereoisomers of compound C.

The C=C group in an alkene contains a -bond.

Complete the diagram below to show how p-orbitals are involved in the formation of a -bond.

Compound D, shown below, reacts with hydrogen bromide by electrophilic addition. A mixture of two organic compounds, E and F, is formed.

compound D

Suggest how an HBr molecule can act as an electrophile.

Draw the structures of the two organic compounds E and F.

Outline the mechanism of the reaction between compound D and hydrogen bromide to form either compound E or compound F.

Include curly arrows and relevant dipoles.

Which of E or F is the major organic product?

Explain your answer.

Major organic product........

Explanation........

Myrcene, C₁₀H₁₆, is a naturally occurring hydrocarbon containing more than one carbon-carbon double bond.

Reaction of 204 mg of myrcene with hydrogen gas produces a saturated alkane.

Calculate the volume of hydrogen gas, in cm³ and measured at RTP, needed for this reaction.

Show your working.

-Carotene is a naturally occurring unsaturated hydrocarbon found in carrots. A -carotene molecule contains 40 carbon atoms, has two rings, and a branched chain.

0.0200 mol of -carotene reacts with 5.28 dm³ of hydrogen gas to form a saturated hydrocarbon.

Using molecular formulae, construct a balanced equation for this reaction.

Include relevant calculations and reasoning.

Equation........