Introduction to organic chemistry Foundation In science


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Introduction to organic chemistry Foundation In science

  1. 1. Chapter 7 : Introduction to Organic Chemistry
  2. 2. Introduction Elements that make up organic compounds.  Organic chemistry is a branch of chemistry.  It is a study of carbon compounds, other than CO, CO2 etc…  All organic compounds contain carbon and in the majority of cases, also hydrogen.  Some organic compounds also contain elements such as oxygen, nitrogen, phosphorus, sulphur and halogen in their molecules.
  3. 3. Classes of Organic Compounds  The branch of chemistry that deals with carbon compounds is – organic chemistry.  Classes of organic compounds can be distinguished according to functional groups- group of atoms that is largely responsible for the chemical behavior of the parent molecule.  Most organic compounds are derived from hydrocarbon.  There are four types of hydrocarbons – saturated, unsaturated, aliphatic & aromatic.
  4. 4. Types of Hydrocarbon 1. Saturated hydrocarbons The simplest of the hydrocarbon species and are composed entirely of single bonds and are saturated with hydrogen. The general formula for saturated hydrocarbons is CnH2n+2 (assuming non-cyclic structures). 2. Unsaturated hydrocarbons  Have one or more double or triple bonds between carbon atoms. Those with one or more double bonds are called alkenes. Those with one double bond have the formula CnH2n (assuming non-cyclic structures) 3. Aromatic hydrocarbons Hydrocarbons that have at least one aromatic ring. also known as arenes. 4. Aliphatic hydrocarbons Hydrocarbons which do not contain a benzene ring
  5. 5.  Is a group of atoms in a compound, which will involve in the chemical reaction.  the compound with the same functional group will have the same chemical reaction.  Example: The functional group Table 1: The structures of the main functional group
  6. 6. Functional Group  The general formula for various compounds is shown below:
  7. 7. • Is a series of organic compounds with a similar general formula e.g: all alkanes have the general formula of CnH2n+2 • It has the same functional group. • For example, the alkane homologous series: – methane (CH4) – ethane (C2H6) – propane (C3H8) – butane (C4H10), and – pentane (C5H12) Each member differing from the previous one by a CH2 group
  8. 8. No. of C atom 1 General Name 2 Eth- 3 Prop- 4 But- 5 Pent- 6 Hex- 7 Hep- 8 Oct- 9 Non- 10 Dec- Meth- Example: Alkane Alkene Alkyne Alkyl Replace the underlined part to the general name
  9. 9. Classification of Carbon Atoms in Organic Molecules      An alkyl group is a group obtained by removing a hydrogen atom from an alkane. The symbol for an alkyl group is R. R has the general formula CnH2n+1. Example of the alkyl groups are the methyl group, -CH3 and the ethyl group, -C2H5. Carbon atoms in organic molecules can be classified as primary, secondary ,tertiary or quaternary carbons depending on the number of alkyl groups attached to the carbon atom.
  10. 10. Type of carbon atom Formula Comments Primary carbon (1°) Only one alkyl group attached to the carbon atom Secondary carbon (2°) Two alkyl groups attached to the carbon atom Tertiary carbon (3°) Three alkyl groups attached to the carbon atom Quaternary carbon (4°) Four alkyl groups attached to the carbon atom
  11. 11. Molecular & structural formulae – Structural Formula  Not only shows the actual number of atoms in the molecule, it also shows how they are bonded together.  Molecular formula only shows the number of atoms for each element present in one molecule of the compound but does not show how these atoms are arranged.  Examples: Molecular formula – C3H6O
  12. 12.  They are generally 3 different ways of writing the structural formula.
  13. 13. Condensed structural formula  In the condensed structural formula, carbonhydrogen and carbon-carbon single bonds are not shown, but double and triple bonds are shown.  When writing a condensed structural formula, branches in the carbon chain are indicated in parentheses.  Example- CH3CH2CH2CH3 or
  14. 14. Expanded structural formula  The expanded formula shows every atom and type of covalent bond in the molecule.  In writing expanded formula, it is important to remember the types of covalent bonds that can be formed between atoms.  Between C-C  Between C-H  Between C-halogen  Between C-O  Between C-N
  15. 15. Skeletal structures  Skeletal structures do not show carbon and hydrogen atoms or C-H bonds unless they are part of a functional group.  Single covalent bonds are indicated with a single line, double bonds with double lines and triple bonds with triple lines.  The ends of the lines and corners between lines indicate the presence of a carbon atom.  Examples are given below.
  16. 16. Draw the condensed structure for each of the compounds. i) ii) iii) iv)
  17. 17. Isomerism    Organic compounds that have the same molecular formula but different arrangements of atoms are known as isomers. The existence of two or more organic compounds with the same molecular formula but different arrangements of atoms is called isomerism. Generally, there are two types of isomerism: constitutional isomerism and stereoisomerism.   Constitutional ( structural ) isomers have the same molecular formula but different structural formulae. In other words, their atoms are linked together in different sequences.
  18. 18. Constitutional Isomerism  Molecules that have the same molecular formula but different structural formulae.  Constitutional isomerism can be subdivided into 3 categories:    Chain isomerism Positional isomerism Functional group isomerism
  19. 19. Chain Isomerism  Chain isomerism are those which differ in the structure of their carbon chains, that is, they differ in the length of their straight chains or branches. For example, butane has two chain isomers;  Chain isomers possess the same fuctional group, and belong to the same homologous series. Chain isomers have different physical properties, but they have similar chemical properties.
  20. 20. Positional Isomerism  Positional isomers have the same carbon skeleton and belong to the same homologous series but differ in the position of the functional group.  In general, positional isomers have similar chemical properties because they have the same functional group.  However they have different physical properties.  The following are the examples of positional isomerism.    Bromoalkanes with the molecular formula, C3H7Br Alcohols with the molecular formula C3H7OH Alkenes with the molecular formula C5H10 CH3CH2CH2CH2OH Butan-1-ol CH3CHCH2CH3 OH Butan-2-ol
  21. 21. Functional group Isomerism  Functional group isomerism is shown by isomers which have the same molecular formula but contain different functional group.  Types of compounds :  alcohol and ether (C3H8O)  Aldehyde and ketone
  22. 22. Stereoisomerisms  a. a. Stereoisomers have the same molecular formula and the same connectivity but different orientations of their atoms in space. Cis-trans isomerism Enantiomers/ optical isomerism Stereoisomers that are nonsuperimposable mirror images of each other.
  23. 23. Chirality centre & enantiomers      An organic molecule will exhibit optical isomerism or optical activity if it contains at least one chiral carbon atom, that is, a carbon atom attached to four different atoms or groups. A chiral carbon atom is also known as an asymmetric carbon atom and is often shown as ‘C*’. A molecule that contains an asymmetric carbon would have a mirror image that cannot be superimposed on it. In short, the mirror image does not have the same structure and is a stereoisomer. A chiral molecule and its mirror image are called enantiomers or optical isomers.
  24. 24. Enantiomers  Enantiomers have the same structural formula but different spatial arrangement of the atoms.  They are mirror images of each other, but because of the asymmetry of their molecules, the two mirror images cannot be superimposed on each other.  It is important to note that there are two subdivisions of stereoisomers: a) b) Enantiomers (mirror image) Diastereomers (non- mirror image) Diastereomers include cis-trans isomers.
  25. 25. 3-D formula  Spatial arrangements of atoms or groups of atoms within the molecule is significantly important in organic chemistry.  Therefore there are methods of writing structural formula in 3-D projection.  The wedges represents the covalent bond coming out of the plane of the paper.  The dash represents the bond behind the plane of the paper.  The line represents the bond lying in the plane of the paper.
  26. 26. Summary
  27. 27. Functional Groups  Hydrocarbons  Alcohols  Aldehydes & Ketones  Carboxylic Acids  Esters  Amines
  28. 28. Functional Groups Alcohol  The functional group for alcohol is an hydroxyl group (-OH)  Alcohols are classified as primary (1°) , secondary (2°) or tertiary (3°). Aldehydes and Ketones  The functional group of both aldehydes and ketones is the C= O (carbonyl group). Carboxylic Acids  The functional group is a –COOH  Carboxyl : Carbonyl + hydroxyl group.
  29. 29. Esters  Derivative of a carboxylic acid in which the H of the carboxyl group is replaced by a carbon group. Amines (-NH2)  The functional group is an amino group.  Amines are classified as primary (1°) , secondary (2°) or tertiary (3°).
  30. 30. 1. Hydrocarbons compounds that are composed of only carbon and hydrogen.  Examples : alkanes, alkenes, alkyne and arenes.  A saturated hydrocarbon contains only single bonds - alkanes  An unsaturated hydrocarbon may contains double bonds or triple bonds – alkenes and alkynes  Aromatic hydrocarbons, also commonly known as arenes – unsaturated hydrocarbon.  Arenes are compounds which contain benzene or benzene-like ring and have the chemical properties characteristic of benzene.  Organic
  31. 31. Alkanes  General formula for alkanes - CnH2n+2 , n ≥ 1  Nomenclature (IUPAC System) Eg: methane, ethane, propane…….  Condensed formula CH3CH2CH2CH3
  32. 32. IUPAC System 1. 2. 3. 4. 5. The longest chain of carbon atoms is taken as the parent chain. Each substituent is given a name and a number. The number shows the carbon atom of the parent chain to which the substituent is bonded. If there is one substituent, number the parent chain from the end that gives it the lower number. If the same substituent appears more than once, number the parent chain from the end that gives the lower number to the substituent encountered first. If there are two or more different substituents, list them in alphabetical order. Use hyphens to separate numbers from words and commas to separate numbers
  33. 33.  The name of a hydrocarbon has three portions: PREFIX + ROOT + SUFFIX Identifies a group Tells the number Tells the type attached to the of C atoms in of organic main chain and the molecule compound the number of the (the longest and the molecule carbon to which it continuous) represents is attached (functional  have –yl as their group) ending PREFIX = PENDANT + LOCATION 34
  34. 34.  Example: 4 Roots 3 2 meth- 2-methyl but ane Is the PREFIX A1C branch is attached to C – 2 of the main chain Is the ROOT  The main chain has 4 C atoms Is the SUFFIX  The compoun d is an alkane PREFIX + ROOT + SUFFIX 1 eth- 1 No. of C atoms 2 prop- 3 but- 4 pent- 5 hex- 6 hept- 7 oct- 8 non- 9 dec- 10 35
  35. 35. Alkane Formula Boiling point [°C] Melting point [°C] Density [g·cm3] (at 20°C) Methane CH4 -162 -183 gas Ethane C2H6 -89 -172 gas Propane C3H8 -42 -188 gas Butane C4H10 0 -138 gas Pentane C5H12 36 -130 0.626(liquid) Hexane C6H14 69 -95 0.659(liquid) Heptane C7H16 98 -91 0.684(liquid) Octane C8H18 126 -57 0.703(liquid) Nonane C9H20 151 -54 0.718(liquid) Decane C10H22 174 -30 0.730(liquid)
  36. 36. Cycloalkanes • Alkanes whose carbon atoms are joined in rings • General formula for cycloalkanes - CnH2n , n ≥ 3 • Eg: cyclopropane, cyclobutane, cyclopentane, cyclohexane Cyclopropane Cyclopentane Cyclobutane Cyclohexane
  37. 37. Physical properties   The b.p of straight chain alkanes increase steadily with relative molecular mass. The increase in b.p is due to the increasing forces of attraction between molecules of increasing size. Effect of branching on b.p    A branched chain alkane boils at lower temperature than the straight chain alkane with the same number of carbon atoms. This is because the branched chain alkanes are more compact and have smaller surface area, smaller van der Waals forces = low b.p Comparing the b.p of alkanes and cycloalkanes.  The b.p of cycloalkanes are 10 - 15°C higher than the corresponding straight chain.
  38. 38. Alkenes  Contain at least one carbon-carbon double bond.  General formula for alkenes – CnH2n , n ≥ 2  Eg: CH2=CH2  The cis-, trans- system
  39. 39. Nomenclature  Identify and name the parent hydrocarbon  Number the carbon atoms in the main chain  When the carbon chain contains more than 3 carbon atoms, a number is used to indicate the position of ‘=‘  Indicate the positions of the double bond and the substituent. ClCH2CH2CH2
  40. 40.  Contain at least one carbon-carbon triple bond.  General formula for alkynes – CnH2n-2 , n ≥ 2  Eg: 1-butyne, 2-butyne HC H2 C C CH3 But-1-yne H3 C C C But-2-yne CH3
  41. 41.  A hydrocarbon that contains hydroxyl group, -OH  SUFFIX end with – ol  Alcohol with the –OH group attached to the end carbon atom is commonly called propyl alcohol or 1-propanol  The PREFIX 1-indicates that the –OH groups is on the first or end of C atom.  The alcohol with the –OH group attached to the middle carbon atom is commonly called isopropyl alcohol or 2-propanol  The PREFIX 2-indicates that the –OH groups is on the second C atom from the end.
  42. 42. • Example: 1-propanol 2-propanol • Alcohols, R-OH • R is the alkyl group • -OH is the functional group methanol (methyl alcohol) ethanol (ethyl alcohol) 1-propanol (propyl alcohol) 2-propanol (propyl alcohol)
  43. 43. Carbonyl compounds  Aldehyde and ketones are carbonyl compounds because they contain the carbonyl group, C=O  In the carbonyl group, the carbon and oxygen atoms are joined together by a double bond.  Thus, the C=O bond consists of a sigma and a pi bond.  Aldehydes and ketones have the same molecular formula, CnH2nO.  The general formula of aliphatic aldehydes and ketones are shown below.  R and R’ may be alkyl or aryl groups.
  44. 44. Nomenclature Aliphatic aldehydes    The rules for naming aldehydes are similar to those for naming alkanes, except that the final ‘e’ of the corresponding alkane name is dropped and replaces by the suffix ‘al’. The carbon of the aldehyde group is counted as part of the carbon chain. Thus, aldehyde with the formula CH3CHO is called ethanal.
  45. 45. Example: 2,2-dimethylbutanal 4-phenylpentanal
  46. 46. Nomenclature of Ketones  The rules for naming ketone are similar to those for naming alkanes, except that the final ‘e’ of the corresponding alkane name is dropped and replaces by the suffix ‘one’.  The carbon of the ketone group is counted as part of the carbon chain.  When naming the carbon atoms, the carbonyl group is given preference over any substituents.
  47. 47. Example: 2-propanone 2-methyl-4-phenyl-3-pentanone 4-penten-2-one alphabetical order
  48. 48. Carboxylic Acids • term “carboxylic” is derived from “carbonyl” and “hydroxyl”. • carboxylic acid also contain carbonyl group, C=O in its structure O C OH
  49. 49. Nomenclature • count number of carbons in the longest carbon chain containing the – COOH group • replace the –e with the suffix –oic acid • compound containing multiple -COOH groups do not drop the –e but add a di- or tri- to the ending – carboxylic acid or add a di- or tri- to the suffix –oic acid. Structural Formula Condensed Structural Formula O O CH3 C OH CH3 CH2 C OH O HO C CH2 O C OH CH3COOH CH3CH2COOH HOOCCH2COO H IUPAC ethanoic acid propanoic acid propandioic acid Common Name acetic acid - malonic acid
  50. 50. Esters • to create an ester, an alcohol is reacted with a carboxylic acid • an ester is named for its starting materials, the acid and the alcohol • the first part names the alcohol, use the side chain abbreviation, i.e. methyl, ethyl… • the second part names the carboxylic acid • to end the second part change the –ic of the carboxylic acid to -ate Structural Formula Condensed Structural Formula IUPAC Common Name O CH3 C O CH3 CH3COOCH3 methyl ethanoate methyl acetate O O CH3 CH2 C O CH2 CH3 CH3 C O CH3CH2COOCH2C H3 CH3COOC6H5 ethyl propanoate phenyl ethanoate ethyl propyrate phenyl acetate
  51. 51. Aromatic Compounds
  52. 52. Introduction        An organic compound that contains a benzene ring in its molecule is known as an aromatic compound. Aromatic hydrocarbons are sometimes called arenes. Benzene is a colourless compound with a melting point of 6°C and a boiling point of 80°C. Benzene’s molecular formula, C6H6, suggests a high degree of unsaturation. Benzene is remarkably unreactive! When benzene reacts, it does so by substitution in which a hydrogen atom is replaced by an other atom or group of atoms. This unusual stability is called aromaticity.
  53. 53. Resonance   is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula.
  54. 54. Nomenclature A. Monosubstituted Benzenes Monosubstituted alkylbenzenes are named as derivatives of benzene, as for example ethylbenzene. The IUPAC system retains common names for several of the simpler monosubstituted alkylbenzenes. Examples :
  55. 55.  The common names phenol, aniline, benzaldehyde, benzoic acid, and anisole are also retained by the IUPAC system.
  56. 56. B. Disubstituted Benzenes When 2 substituents occur on a benzene ring, three constitutional isomers are possible. The substituents may be located by numbering the atoms of the ring or by using the locators ortho, meta, and para.
  57. 57. Electrophilic Substitution Reactions + +
  58. 58. Halogenation of benzene  Benzene does not react with chlorine in the dark.  However in the presence of catalyst, a substitution reaction occurs when chlorine reacts with benzene at room temperature to form chlorobenzene and steamy fumes of hydrogen chloride.
  59. 59. Bromination + +
  60. 60. Nitration of benzene nitronium
  61. 61. Friedel-Crafts alkylation
  62. 62. Friedel-Crafts acylation  In the presence of anhydrous aluminium chloride, benzene reacts with an acyl chloride or an acid anhydride (RCO-O-COR) to form a ketone.  An example of an acyl chloride is ethanoyl chloride and an example of an acid anhydride is ethanoic anhydride.
  63. 63. Summary  Electrophilic Aromatic Substitution Halogenation : 2 Nitration :
  64. 64. Friedel-Crafts acylation Friedel-Crafts alkylation
  65. 65. Reactions of benzene derivatives Toluene  The methyl group activates the benzene nucleus.  Hence, toluene reacts considerably faster than benzene in all electrophilic substitutions.  Toluene undergoes reactions in the methyl side chain or the benzene ring, depending on 2 factors:   The type of reagent used The conditions of the reaction
  66. 66. i- Oxidation of alkylbenzenes  If toluene is refluxed with a strong oxidising agent, K2Cr2O7 or KMnO4 , the side chain is oxidised to – COOH and benzoic acid is formed.
  67. 67.  If a milder oxidising agent is used, such as manganese(IV) oxide or chromium(VI) dichloride oxide, CrO2Cl2, the side chain of –CH3 is oxidised to the aldehyde group - CHO
  68. 68. Halogenation of toluene  Side chain substitution  Benzene ring CH3
  69. 69. Introduction to amines  Organic compounds derived by replacing one or more of the H atoms in ammonia with alkyl or aryl groups are called amines. Class Primary (1 o ) Secondary (2o ) Tertiary (3 o ) General formula
  70. 70. IUPAC Nomenclature Primary Amines  In IUPAC nomenclature, the suffix ‘amine’ replaces the final ‘e’ in the name of the parent alkane, for example,  The prefix ‘amino’ is used to indicate the presence of an –NH 2 group in a molecule containing more than one functional group.
  71. 71. Aromatic primary amines Secondary & tertiary amines
  72. 72. B.P of Amines    The b.p increase with increasing relative molecular mass. Amines are polar compounds and both primary and secondary amines associate by H-bonding. For isomeric amines, the b.p decrease in the order 1o amine > 2o amine > 3o amine THIS IS DUE TO THE PROGRESSIVE DECREASE IN H-BONDING    The b.p of aliphatic amines are higher than those alkanes or haloalkanes of similar mass due to H-bonding. The H-bond in amine is more polar than H-bond in alkane but less polar than O-H. Hence, H-bond in amine is weaker than that of alcohols or carboxylic acids.
  73. 73.  All three classes of aliphatic amines are capable of forming Hydrogen bonds with water molecules. The Basicity of amines  According to Bronsted-Lowry theory, a basic is a proton acceptor. RNH2 (aq) + H2O (I)    RNH3+ (aq) + OH- (aq) The base dissociation constant or basicity constant, K b or pKb are given by the following expressions. The larger the value of Kb, the greater the tendency of the amine to accept a proton from water, thus the stronger the base. Conversely, the smaller the value of pKb, the stronger the base.
  74. 74. We notice that mostly primary aliphatic amines are somewhat stronger bases than ammonia because the alkyl group is electron donating. [RNH3+] [OH-] mol dm-3 Kb = [RNH2] pKb = - log Kb Examples, Ammonia - Kb = 1.8 x 10-5 pKb = 4.74 Methylamine – Kb = 4.4 x 10-4 pKb = 3.36 Benzylamine - Kb = 2.2 x 10-5 pKb = 4.66
  75. 75. Preparation of Amines  Reduction of nitro compounds.  This method is particularly useful for producing aromatic amines from aromatic nitro compounds. For example, aniline is prepared by the reduction of nitrobenzene using    Tin and concentrated hydrochloric acid Zinc and hydrochloric acid Tin(II) chloride, SnCl2, in hydrochloric acid
  76. 76.  Reduction of Nitriles  Primary aliphatic amines can be obtained by the reduction of nitriles using the following reagents.   Lithium aluminium hydride in ethoxyethane Hydrogen in the presence of a nickel catalyst at 140oC ( catalytic hydrogenation) When the vapour of propanitrile is mixed with hydrogen and passed over a nickel catalyst at a temperature of 140 celcius, reduction takes place and propylamine is formed. CH3CH2C≡N + 2H2 Ni, 140oC CH3CH2CH2NH2
  77. 77.  Reduction  of Amides Primary amines, secondary amines and tertiary amines are also formed by the reduction of primary amides with LiAlH 4
  78. 78.  Hofmann degradation of Amides  On warming a primary amide with bromine in a solution of NaOH, a primary amine is formed.  In this reaction, the C=O group from the amide is removed and the primary amine is formed.  The elimination of a C=O group provides a means of shortening the length of a carbon chain by one carbon atom. RCONH2 + Br2 + 4NaOH RNH2 + 2NaBr + Na2CO3 + 2H2O
  79. 79. Amino Acids  Organic compounds that possess both the amino group and the carboxyl group are called amino acids.  Almost all occurring amino acids are α-amino acids.  These are amino acids in which both the amino and carboxyl groups are attached to the α- carbon atom of a carboxylic acid.  The α- carbon is the carbon atom next to the carbonyl group.
  80. 80.  Amino acids can be classified as neutral, basic or acidic, depending on the number of –NH2 and – COOH groups present in the molecule.  Neutral  Basic – 1 COOH and 1 NH2 present - NH2 > COOH  Acidic - NH2 < COOH
  81. 81. 1. Classify each amine as primary, secondary, or tertiary. i) ii)
  82. 82. b) Name the following α-amino acids using the IUPAC nomenclature: i) ii) iii) iv)
  83. 83. Zwitterion        Amino acids – white crystalline solids, high b.p & m.p. Amino acids dissolve in water to form neutral solutions but have low solubility in organic solvents such as ethanol. These 2 properties indicate that amino acids exist as a polar ions. A dipolar ions is also known as zwitterion or an internal salt. Zwitterion – any ion that carries both a positive and negative charge on the same group of atoms is called zwitterion. In neutral solutions and in the solid state, a.a exist as zwitterions. A zwitterion is formed when a proton from the –COOH group is donated to the –NH2 group of the same molecule.
  84. 84. A zwitterion is amphoteric in nature.  It acts as a base in the presence of an acid and as an acid in the presence of a base.  Therefore in an acidic solution, the cation H3N+ – CH2 – COOH predominates.  In an alkaline solution, the anion H2N – CH2 – COOpredominates.  In a neutral solution, the zwitterion H3N+ – CH2 – COOpredominates
  85. 85. 87 Amino acids are the basic structural units of proteins. • Contain at least one amino group (-NH2) • And at least one carboxyl group (-COOH) •Existing form is pH dependent
  86. 86. 88 Amino acids are joined in a protein by the formation of a peptide bond H C H3N C H O + H3N O C O C O R1 R1 Peptide (amide) bond H H3N O C C R1 H O N C C H R1 O + Dipeptide – contains two amino acid residues H2O planar
  87. 87. 89 20 amino acids can form 202 or 400 dipeptides. Protein with 50 amino acid residues can be arranged in 2050 or 1065 ways.
  88. 88. Importance of amino acids  There are about 22 amino acids that are mostly found in nature.  Only 20 of these a.a are required to synthesise proteins.  However there are 8 a.a, known as essential a.a which cannot be synthesised by human body and must be obtained from the proteins in the diet. Type of protein Fuction in the body Example Structural Provide structural components Collagen in tendons and cartilage; Keratin in hair, skin and nails. Transport Carry essential substances Haemoglobin in the blood throughout the body transports oxygen Hormone Regulate body metabolism Insulin regulates blood glucose level Enzyme Catalyse biochemical Trypin catalyses the hydrolysis
  89. 89. Introduction to Polymers  Monomers – are small molecules used to synthesis polymers.  Polymer – a large molecule made up of many smaller molecules (monomer).  Polymerisation The chemical reaction in which the monomers are joined together by covalent bonds.
  90. 90. Homopolymer & Copolymer  Homopolymers Polymers synthesised from a single type of monomer. Ex: polyethylene, polypropylene.  Copolymers polymers formed from 2 or more different types of monomers. Ex: nylon 6.6, Terylene CH2-CH2 H C CH-CH-CH=CH-CH3 n polyethylene Styrene-butadiene rubber n
  91. 91. Natural Polymers  Examples of natural polymers are proteins, carbohydrates and natural rubber. Tetrapeptide - protein Lactose - carbohydrate Isoprene – natural rubber
  92. 92. Preparation of synthethic polymers Condensation polymerisation Addition polymerisation The chemical process in which 2 monomers react to form a large molecule and eliminate a smaller molecule (usually water, ammonia) The addition reaction in which monomers with double bonds are joined together by covalent bonds to form a large molecule without a loss of a small molecule. The monomers must have at least 2 functional groups to act as the reactive ends. Monomers for making addition polymers may be alkenes or alkene derivatives. Examples: Kevlar, Nylon and Terylene. Examples: polyvinyl chloride, polystyrene
  93. 93. Kevlar  Is an aramide (aromatic polyamide) prepared by the reaction of 1,4-benzenedicarboxylic acid (terephthalic acid) with 1,4-diaminobenzene.  It is a very strong material and is used for bulletproof vests.
  94. 94. Nylon 6  Nylon 6 is produced by the prolonged heating of caprolactam with a trace of water. OR HOOC-(CH2)5- NH2 (6-aminohexanoic acid)
  95. 95. PVC  The monomer for making polyvinyl chloride (PVC) is vinyl chloride.  The IUPAC name for polyvinyl chloride is poly(chloroethene), while the IUPAC name for vinyl chloride is chloroethene.
  96. 96. Polystyrene (PS)  The monomer for making polysyrene (PS) is styrene.  The IUPAC name for polystyrene is poly(phenylethene), while the IUPAC name for styrene is phenylethene, C6H5CH=CH2