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Booklet to help with unit 28 P5 M4

Booklet to help with unit 28 P5 M4. Isomers and their importance in society. Isomerism. Structural isomerism. This is when two or more molecules have the same molecular formula but different structural arrangement of atoms. There are three types of structural isomerism you need to know about:

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Booklet to help with unit 28 P5 M4

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  1. Booklet to help with unit 28 P5 M4 Isomers and their importance in society

  2. Isomerism

  3. Structural isomerism • This is when two or more molecules have the same molecular formula but different structural arrangement of atoms. • There are three types of structural isomerism you need to know about: Chain isomerism Positional isomerism Functional group isomerism

  4. Chain isomerism • Chain isomerism occurs when the way carbon atoms are linked together is different from compound to compound. • It is also called nuclear isomerism.

  5. Positional isomerism • Positional isomerism occurs when functional groups are in different positions on the same carbon chain

  6. Functional isomerism • Functional isomerism occurs when substances have the same molecular formula but different functional groups. This means that functional isomers belong to different homologous series Ethanol Dimethyl ether C2H6O Alcohols have the hydroxyl group,–OH. Ethers have the functional group R–O–R'

  7. Stereoisomerism • Stereo-isomerism occurs when the atoms in a molecule can have different arrangements in space. • There are two types of stereo-isomerism: geometrical isomerism and optical isomerism. • Geometrical isomers can have very different physical properties, such as different melting points, but they tend to have the same chemical properties. • Optical isomers have the same chemical and physical properties, except that different enzymes will react with different optical isomers because the active site of enzymes are very specific.

  8. Geometric isomerism (cis/trans) • This occurs when substances have the same molecular formula, but a different arrangement of their atoms in space. There are three ways that this can happen: • where there is a C=C bond in the molecule • where a molecule has rings; or • where there is a >C=N bond

  9. Optical isomerism • It occurs when substances have the same molecular and structural formulae, but one cannot be superimposed on the other- they are mirror images of each other. • There must be a chiral centre where an asymetric atom (In organic chemistry this is usually carbon) is bonded to four different groups. This is an amino acid also known as alanine The two molecules that arise as a result of optical isomers are called enantiomers

  10. why it is commercially important to understand about isomerism • In living systems, molecules that carry out specific functions exist as a one isomer only. • The reason for this is because these molecules are synthesised using enzymes, and enzymes are catalysts that can recognise other isomers as different molecules. Other isomers will not fit onto the active sites used by the enzymes to catalyse reactions and synthesise organic molecules

  11. why it is commercially important to understand about isomerism • Pharmaceutical products acting on living systems often require the synthesis of single isomers. • One isomer of a commercially made pharmaceutical products may be more effective than the other. Also one isomer may even be toxic to living systems.

  12. Task 1 Complete “worksheet to help with unit 28 P5”

  13. Laboratory synthesis of optical isomers • Living systems often require the synthesis of single optical isomers. As well as the effectiveness of the drug or chemical (e.g. perfume) toxicity has to be taken into account

  14. Some website pages on thalidomide http://www.bbc.co.uk/news/health-24472269 http://www.bbc.co.uk/news/world-asia-25181380 http://www.sciencemuseum.org.uk/broughttolife/themes/controversies/thalidomide.aspx http://www.chm.bris.ac.uk/motm/thalidomide/start.html http://lawrencekok.blogspot.co.uk/2011/06/ib-chemistry-stereoisomerism-optical.html http://web.clark.edu/ggrey/chemstruct/organic/optical_isomers.htm

  15. Task 2 Select a well-documented example of optical isomers which have different chemical/therapeutic properties and use this example to discuss the chemical/ therapeutic importance of isomerism • Discuss what thalidomide is- it’s original use and what it ended up being used for in 1950’s/60’s • Discuss the negative effect that thalidomide had • Include the structure of thalidomide • Discuss the optical isomers and how they had different effects on living systems • Explain why it is important for us to understand optical isomerism – relate your explanation to thalidomide

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