Isomerism

This question is about isomerism.

Compound L has this structure.

Use IUPAC rules to name L.

Explain why L exists as stereoisomers.

Compound M has the same carbon chain as L but the double bond is in a different position.

M also exists as stereoisomers.

Draw the structural formula of M.

Explain why M exists as stereoisomers.

Structural formula

Figure 1 shows part of the mechanism when L reacts with hydrogen bromide.

Complete Figure 1 to show the next step in the mechanism that gives the

This question is about rapeseed oil.

Figure 2 shows the structure of compound Q found in rapeseed oil. Each branch in the molecule is formed from a different long-chain carboxylic acid.

State the type of stereoisomerism shown in Branch A.

Q can be reacted with methanol to form three different esters.

State the number used to identify the position of the C=C bond in the name of the ester formed from Branch A.

State the number of different stereoisomers of the ester formed from Branch B.

Give a use for these esters.

Number used in the name of the ester

Number of stereoisomers

Q also reacts with NaOH

State the formula of the product, formed by Branch B in Figure 2, in this reaction.

State a use for this product.

Compound Y has the structural formula CH₃COOCH₂CH(CH₃)₂

Which compound is a position isomer of Y ?

Which compound shows E – Z isomerism?

This question is about isomerism and the dehydration of alcohols.

Pentan-2-ol has the molecular formula C₅H₁₂O

Draw the displayed formula of an unbranched position isomer of pentan-2-ol that can be dehydrated to form a single alkene.

Draw the skeletal formula of a chain isomer of pentan-2-ol that can be dehydrated to form a mixture of alkenes.

Draw the structure of an unbranched functional group isomer of pentan-2-ol.

Another isomer of pentan-2-ol is an alcohol that is not dehydrated when heated with concentrated sulfuric acid.

Draw the structure of this isomer.

An incomplete mechanism for the dehydration of a compound is shown.

Complete the mechanism for this reaction by drawing two curly arrows on the intermediate.

Name the mechanism for this reaction.

An isomer of the final product can also form in the reaction in Question 02.5.

Draw the structure of this isomer.

This question is about 2-methylbut-1-ene.

Name the mechanism for the reaction of 2-methylbut-1-ene with concentrated sulfuric acid.

Outline the mechanism for this reaction to form the major product.

Outline of mechanism to form major product

Draw the structure of the minor product formed in the reaction in Question 03.1

Explain why this is the minor product.

Structure of minor product

Draw the skeletal formula of a functional group isomer of 2-methylbut-1-ene.

2-methylbut-1-ene can form a polymer.

State the type of polymerisation.

Draw the repeating unit for the polymer formed.

Type of polymerisation

Repeating unit

Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to produce a mixture of five products, A, B, C, D and E.

Products A, B and C are alkenes.

A is a structural isomer of B and C.

A does not exhibit stereoisomerism.

B and C are a pair of stereoisomers.

Products D and E are alcohols.

D and E are a pair of enantiomers.

Give the names of the two concurrent mechanisms responsible for the formation of the alkenes and the alcohols.

Mechanism to form alkenes

Mechanism to form alcohols

Define the term stereoisomers.

Deduce the name of isomer A.

Explain why A does not exhibit stereoisomerism.

Outline the mechanism for the reaction of 2-bromobutane with sodium hydroxide to form alkene A.

Deduce the name of isomer B and the name of isomer C.

Explain the origin of the stereoisomerism in B and C.

Draw 3D representations of enantiomers D and E to show how their structures are related.

A student compares the rates of hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane.

The suggested method is:

• add equal volumes of the three halogenoalkanes to separate test tubes

• add equal volumes of aqueous silver nitrate to each test tube

• record the time taken for a precipitate to appear in each test tube.

State and explain the order in which precipitates appear.

Order in which precipitates appear

Which compound is an isomer of ethyl ethanoate?

This question is about isomers with the molecular formula C₅H₁₀O

Draw the skeletal formula of a branched chain aldehyde with molecular formula C₅H₁₀O that is optically active.

Describe how you distinguish between separate samples of the two enantiomers of the branched chain aldehyde C₅H₁₀O

Draw the E and Z forms of a structural isomer of C₅H₁₀O that shows both optical and geometric isomerism.

Isomer J is cyclic and has an ether functional group (C–O–C) Isomer J has only three peaks in its¹³C NMR spectrum.

Draw two other cyclic isomers of C₅H₁₀O that have an ether functional group and only three peaks in their¹³C NMR spectra.

Which compound has E – Z isomers?

This question is about the structural isomers shown.

Identify the isomer(s) that would react when warmed with acidified potassium dichromate(VI).

State the expected observation when acidified potassium dichromate(VI) reacts.

Expected observation

State the type of structural isomerism shown by isomers P, Q, R and S.

Describe fully how infrared spectra can be used to distinguish between isomers R, S and T. Use data from Table A in the Data Booklet in your answer.

State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers.

Which has E - Z isomers?

The outer layers of some golf balls are made from a polymer called polyisoprene. The isoprene monomer is a non-cyclic branched hydrocarbon that contains 88.2 % carbon by mass. The empirical formula of isoprene is the same as its molecular formula.

Deduce the molecular formula of isoprene and suggest a possible structure.

Molecular formula

Structure

The insides of some golf balls are made from a mixture of three other polymers. The repeating unit for one of these polymers is shown.

Draw the skeletal formula of the monomer used to make this polymer.

Give the IUPAC name of the monomer.

Skeletal formula of monomer

A second polymer in the mixture has a repeating unit with the structure shown.

The third polymer in the mixture is a stereoisomer of this polymer.

Draw the structure of the repeating unit of the third polymer.

Give a reason why this type of stereoisomerism arises.

Repeating unit

Golf balls recovered from lakes and ponds can be used again even after being in water for several years.

Explain why these golf balls do not biodegrade.

This question is about esters including biodiesel.

An ester is formed by the reaction of an acid anhydride with CH₃CH₂OH

Complete the equation. In your answer show clearly the structure of the ester. Give the IUPAC name of the ester.

In a reaction to form biodiesel, one mole of a vegetable oil reacts with an excess of methanol to form two moles of an ester with molecular formula C₁₉H₃₄O₂ and one mole of an ester with molecular formula C₁₉H₃₆O₂

Draw the structure of the vegetable oil showing clearly the ester links.

You should represent the hydrocarbon chains in the form C_xH_y where x and y are the actual numbers of carbon and hydrogen atoms.

The compound C₁₉H₃₄O₂ is the methyl ester of Z,Z-octadeca-9,12-dienoic acid.

Part of the structure of the acid is shown.

Complete the skeletal formula to show the next part of the hydrocarbon chain to carbon atom number 14. In your answer, show the Z stereochemistry around both C=C double bonds.

Give an equation for the complete combustion of the ester C₁₉H₃₄O₂

Combustion of biodiesel produces greenhouse gases such as carbon dioxide that cause global warming. Part of the infrared spectrum of carbon dioxide is shown in Figure 3.

State how the infrared spectrum of carbon dioxide in Figure 3 is not what you might predict from the data provided in Table A in the Data Booklet.

Explain how carbon dioxide causes global warming.

How many structural isomers with the molecular formula C₅H₁₀O react with Tollens’

Give the full IUPAC name of isomer P.

A sample of P was mixed with an excess of oxygen and the mixture ignited. After cooling to the original temperature, the total volume of gas remaining was

When this gas mixture was passed through aqueous sodium hydroxide, the carbon dioxide reacted and the volume of gas decreased to 155 cm³

Both gas volumes were measured at 25 °C and 105 kPa

Write an equation for the combustion of P in an excess of oxygen and calculate the mass, in mg, of P used.

The gas constant R = 8.31 J K⁻¹ mol⁻¹

Mass of P used mg

Isomer Q (C₆H₁₀O₂) is a cyclic compound. The infrared spectrum of Q is shown in Figure 4 and the¹³C NMR spectrum of Q is shown in Figure 5.

Use these spectra and Tables A and C in the Data Booklet to deduce the structure of Q. In your answer, state one piece of evidence you have used from each spectrum.

Structure of Q.

Evidence from Figure 4

Evidence from Figure 5

Isomers R and S are shown.

Although the¹³C spectra of R and S both show the same number of peaks, the spectra can be used to distinguish between the isomers.

Justify this statement using Table C from the Data Booklet.

Give the number of peaks for each isomer.

Justification

Although the¹H spectra of R and S both show the same number of peaks, the spectra can be used to distinguish between the isomers.

Justify this statement using the splitting patterns of the peaks.

Give the number of peaks for each isomer.

Justification

The action of heat on 5-hydroxyhexanoic acid can lead to two different products.

On gentle heating, 5-hydroxyhexanoic acid loses water to form a cyclic

Under different conditions, 5-hydroxyhexanoic acid forms a polyester.

Draw the structure of T.

Draw the repeating unit of the polyester and name the type of polymerisation.

Structure of T

Repeating unit of polyester

Type of polymerisation

Isomer U is shown.

The polymer formed by U and the polymer formed by 5-hydroxyhexanoic acid in Question 10.6 both contain ester groups that can be hydrolysed.

Draw the repeating unit of the polymer formed by U.

Justify the statement that, although both polymer structures contain ester groups, the polymer formed by U is not biodegradable.

Repeating unit of polymer formed by U.

Justification