Isomerism: Structural Isomerism & Stereoisomerism (Cambridge (CIE) AS Chemistry)

A chemist is analysing a collection of organic compounds.

Some of these compounds are shown in Table 1.1.

 Table 1.1

Compound	IUPAC name	Displayed formula	Skeletal formula
1	Z-2-chloro-but-2-en-1-ol
2	2-chloropropanal
3
4

Complete Table 1.1.

State the empirical formula of compound 1.

Explain why compound 1 exists as two stereoisomers, but compound 4 does not.

Compounds 2 and 3 both exhibit the same type of isomerism.

i) State the type of isomerism shown by compounds 2 and 3.  

[1] 

ii) Draw the two isomers of compound 2 to explain how this type of isomerism occurs. 

[3]

There are many different chemicals with the same molecular formulae but different arrangements of atoms in three-dimensional space. 

i) Name the shortest straight-chain alkane to have structural isomers and the isomer. 

[2]

 ii) State the type of isomerism shown by the isomers in part (i). 

[1]

C₄H₈ exists as several isomers. 

i) Name the homologous series that C₄H₈ belongs to.  

 [1]

 ii) Draw the skeletal formulae of two cyclic C₄H₈ isomers and two C₄H₈ isomers that show cis / trans isomerism. 

[4]

iii) There are two unsaturated C₄H₈ isomers that do not show cis / trans isomerism. Name these isomers and explain why they do not show cis / trans isomerism. 

[2]

Draw the displayed formulae of the following compounds and, where appropriate, identify any chiral centres. 

• 2,4-dimethylhexan-3-ol

• 2,4-dimethyl-3-chloropentane

• 2-aminobutane

1-bromopropan-1-ol exhibits optical isomerism.

Draw 3D representations of the two enantiomers of 1-bromopropan-1-ol.

Butan-2-ol is used as a solvent, in industrial cleaners, in paint removers and in the manufacture of other chemicals such as butanone.

Draw the fully displayed formula of butan-2-ol and the positional isomer of butan-2-ol.

Name the branch chain isomers of butan-2-ol.

Explain why butan-2-ol does not exhibit stereoisomerism.

The organic compounds in Fig 1.1 are all made by living organisms.

Fig. 1.1

i) Give the name of compound A. 

[1]

ii) Compound A has two chiral centres and forms stereoisomers. 

Draw one pair of optical isomers of compound A using the conventional three-dimensional representation.

     [2]

Compounds B, C, D and E all show the same type of isomerism.

Circle the functional group(s) responsible for this isomerism on the molecules in Fig 1.1.

Compound D reacts with hydrogen chloride to form two products.

i) Fully name the type of mechanism for this reaction. 

[1]

ii) One of the products formed exists as a pair of stereoisomers. 

Draw three-dimensional diagrams of the pair of stereoisomers formed during this reaction.

 Indicate with an asterisk (*) the chiral centre on one of the structures drawn. 

       [3]

Name the type of reaction occurring when compound E reacts to form methanol and deca-2,4-dienoic acid.