Alkenes

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.

Hydrogen reacts much more readily with alkenes than with alkanes.

Why is this?

A Alkenes are polar molecules whereas alkanes are not.

B All atoms in an alkane have a full outer shell of electrons.

C The bond enthalpy of C–C bonds is higher than that of bonds.

D The bond enthalpy of C–C bonds is lower than that of bonds.

The structure of but-1-ene is shown below.

Which row has the correct shape around carbon atoms labelled x and y ?

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.

Which statement about bonds is correct?

A The C=C bond in ethene is more polar than the C−C bond in ethane.

B A -bond is stronger than a -bond.

C The H−C−H bond angle in ethane is greater than the H−C−H bond angle in ethene.

D A -bond is formed from sideways overlap of p orbitals.

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.

Which types of bonds are broken and formed in the reaction of ethene and bromine?

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........