PRP 1016 Chemistry 1 Learning Unit 7: Organic Chemistry I PDF

Personal Use Only. Not For Sale Centre for Pre-University Studies PRP 1016 CHEMISTRY 1 LEARNING UNIT 7: ORGANIC CHEMISTRY I PREPARED BY...

Personal Use Only. Not For Sale Centre for Pre-University Studies PRP 1016 CHEMISTRY 1 LEARNING UNIT 7: ORGANIC CHEMISTRY I PREPARED BY 1 ESWARAN MADIAHLAGAN  Personal Use Only. Not For Sale Centre for Pre-University Studies CONTENT 7.1 Introduction to Organic Chemistry 7.2 Aliphatic Hydrocarbons: Alkanes 7.3 Aliphatic Hydrocarbons : Alkenes 7.4 Aromatic Hydrocarbon: Benzene 2  Personal Use Only. Not For Sale Centre for Pre-University Studies LEARNING UNIT 7.1: INTRODUCTION TO ORGANIC CHEMISTRY LEARNING OBJECTIVES (7.1)  Describe the properties of carbon atom  Differentiate functional groups and classify the homologous series  Represent organic compounds by using various chemical formulae  Name organic compounds according to the IUPAC system 3  Personal Use Only. Not For Sale Centre for Pre-University Studies What is Organic Chemistry? ORGANIC HYDROCARBON THE STUDY OF COMPOUND COMPOUND 4  Personal Use Only. Not For Sale Centre for Pre-University Studies Properties of Carbon Atom Forms four (4) covalent bonds via sharing of its valence electrons Tetravalent Requires four (4) additional electron to achieve octet configuration electrons 5  Personal Use Only. Not For Sale Centre for Pre-University Studies Properties of Carbon Atom The C-C bonds are relatively strong bonds (ref. LU 5 – Catenation – Group 14 Element Properties) Forms a diversity of organic compounds: I. Consists of long carbon chains or ring structures II. Consists of many different groups or elements. 6  Personal Use Only. Not For Sale Centre for Pre-University Studies Classifications of Organic Compounds Aliphati c Homologous series Based Arrangement On : of carbon Alicycli chain Saturate c d Presence of double or triple bond Arene Unsaturated 7  Personal Use Only. Not For Sale Centre for Pre-University Studies Arrangement of Carbon Propane Cyclobutane Benzene Aliphatic Alicyclic Arene Open chain arrangement. Consists of closed ring(s) Consist of at least one Non-cyclic. of carbon atoms. benzene ring. 8  Personal Use Only. Not For Sale Centre for Pre-University Studies Presence of Multiple Bond Saturated Compound Unsaturated Compound Butane But-1-ene Contains only carbon-carbon single bonds Contains one or more double or triple carbon-carbon bonds. 9  Personal Use Only. Not For Sale Centre for Pre-University Studies Functional group is atom or group of atoms that are responsible for the chemical properties of organic molecules. Functional Groups & Homologou s Series Organic compounds with the same functional groups belong to the same homologous series. 10  Personal Use Only. Not For Sale Centre for Pre-University Studies Functional Groups and Homologous Series Homologous Series General Formula Functional Group Carbon- Alkanes CnH2n+2 C C carbon single bond Carbon- Alkenes CnH2n C C carbon double bond Carbon- Alkynes CnH2n–2 C C carbon triple bond Alkyl Halides CnH2n+1X C X Halide (X is halogen) 11  Personal Use Only. Not For Sale Centre for Pre-University Studies Functional Groups and Homologous Series Homologous Series General Formula Functional Group Hydroxyl Alcohols CnH2n+2O C O H group O Carbonyl Aldehydes CnH2nO H group C O Carbonyl Ketones CnH2nO C C C group O Carboxyl Carboxylic Acids CnH2n+1X group C O H 12  Personal Use Only. Not For Sale Centre for Pre-University Studies Functional Groups and Homologous Series Homologous Functional Example Series Group Amine CH3CH2NH2 C N Amine group s Ethylamine O CH3CONH2 Amide C N Amide group s Ethylamine O Ester C O C Carboxylate CH3COOCH2CH3 s group Ethyl ethanoate Alkoxy group CH3OCH3 Ether C O C bonded to Methoxymethane s carbon Nitrile C N CH3CN Cyano group Ethanenitrile s 13  Personal Use Only. Not For Sale Centre for Pre-University Studies Homologous Series Show an increase of 14 Can be represented by the same general formula 1 4 mass units in their RMM from the previous member Can be prepared by the same method All members RMMpropene=42 in Example: all alcohols can be prepared by the 2 homologous RMMbutene = 56 hydrolysis of alkyl series: halides Have the same chemical Show gradual change in properties 3 5 physical properties with Example: all aldehydes increasing RMM can be oxidised b.p.ethanol = 78˚C b.p.propanol = 97˚C 14  Personal Use Only. Not For Sale Centre for Pre-University Studies Exercise 1  Identify the homologous series of each of the following compound: 1. CH3CH2CHCH2 6. CH3CH2OCH2CH3 2. CH3CH(CH3)CH2CH3 7. CH3CH2Cl 3. CH3CH(OH)CH3 8. CH3CCCH3 4. CH3CH2NH2 9. CH3CH2COOH 5. CH3CH2COCH3 10. CH3COOCH3 15  Personal Use Only. Not For Sale Centre for Pre-University Studies Representing Organic Compounds Besides molecular formula, organic compounds often represented by structural formula. Structural formula shows:  the number and types of atoms present.  the arrangement of the atoms. Basic Structural Condensed Formula Skeletal Formula Formula Displayed Formula 16  Personal Use Only. Not For Sale Centre for Pre-University Studies Structural Formula Basic Structural Condensed Formula Skeletal Formula Formula Displayed Formula Shows all atoms present and their Not showing any C atoms position. and H atoms attached to the C. Not showing any Carbon atoms are bonds. represented by the junctions between the bonds. Shows only functional Shows all the atoms and their position. groups. Shows all type of bonds present. 17  Personal Use Only. Not For Sale Centre for Pre-University Studies Detailed Structural Formula Straight lines  show atoms and bonds Dashed lines that are in the same plane  show atoms and bonds (of paper). that go into the page, behind the plane, away from you. Wedged lines  show atoms and bonds that come out of the page, in front of the plane, toward you 18  Personal Use Only. Not For Sale Centre for Pre-University Studies Exercise 2  Complete the table below: Molecular Condensed Displayed Skeletal Formula Formula Formula Formula C5H10 CH3CH2CHCHCH3 H H H H C4H9Cl H C C C C H H Cl H H C3H7OH OH 19  Personal Use Only. Not For Sale Centre for Pre-University Studies IUPAC Nomenclature Naming System That Shows Compounds : Homologous Series/ Functional Chain, branch or ring present Groups Other atoms aside from the Number of carbon atoms carbon The naming system enables the reader to derive the name of a given compound from its IUPAC name. 20  Personal Use Only. Not For Sale Centre for Pre-University Studies IUPAC Nomenclature Shows the position Shows the number of the alkyl branch of carbon atoms in alkyl Shows the position of the functional on the hydrocarbon branch attached to the group on the hydrocarbon backbone hydrocarbon backbone backbone Shows the position of other 4-Bromo-3-methylhex-2-ene atom/substituent attached on the Suffix: hydrocarbon Shows the functional backbone Shows other atom Prefix (parent name): group or homologous (substituent) presents Shows number of series in the compound carbon atoms in the (aside from carbon) longest continuous hydrocarbon chain (hydrocarbon backbone) 21  Personal Use Only. Not For Sale IUPAC Nomenclature Centre for Pre-University Studies Number of carbon atoms Prefix In the hydrocarbon backbone Meth- 1 Eth- 2 Prop- 3 But- 4 Pent- 5 The Prefix Hex- 6 Hept- 7 Oct- 8 Non- 9 Dec- 10 Undec- 11 Dodec- 12 Tridec- 13 Eicos- 20 22  Personal Use Only. Not For Sale IUPAC Nomenclature Centre for Pre-University Studies Suffix Homologous Series -ane Alkane -ene Alkene -yne Alkyne -ol Alcohol The Suffix -oic Carboxylic acid -al Aldehyde -one Ketone -oate Ester 23  Personal Use Only. Not For Sale IUPAC Nomenclature Centre for Pre-University Studies Carboxylic acid Ester Amide Aldehyde Ketone Priority of Functional Alcohol Increasing Group Amine general priority for Alkyne nomenclature Alkene Alkane Ether Alkyl halide 24  Personal Use Only. Not For Sale IUPAC Nomenclature Centre for Pre-University Studies Name of Condensed formula of some alkyl alkyl group Example H H C H Methyl CH3- H H H H H C C C C C H H H H H H H The Alkyl Group H H C C H H Ethyl CH3CH2- H H H H An alkane that has lost a hydrogen H C C C C C H atom and joined/attached to the H H H H H hydrocarbon backbone Propyl CH3CH2CH2- Butyl CH3CH2CH2CH2- 25  Personal Use Only. Not For Sale Centre for Pre-University Studies Basic Rules of IUPAC Nomenclature Find the longest continuous Number the backbone hydrocarbon chain that 2 beginning with the consists of functional group 1 end nearer to the (the backbone). 7 9 functional group or nearer This will determine 8 to branch (for alkane). the parent name. 6 3 1 5 4 2 E If more than one M substituents are attached, Name and locate the name the compound by position of substituent/ including the substituents in branch corresponding alphabetical order (ignore 5-ethyl- 2-metyl nonane to its location on the numbering), backbone. For more than 1 Butyl, ethyl, hexyl, methyl, similar substituents, use pentyl 4 3 prefix: & propyl di- for 2 (dimethyl) 26 tri-for 3 (trimethyl)  Personal Use Only. Not For Sale Centre for Pre-University Studies Exercise 3  State the IUPAC name of the following compounds: 27  Personal Use Only. Not For Sale Centre for Pre-University Studies LEARNING UNIT 7.1: INTRODUCTION TO ORGANIC CHEMISTRY LEARNING OBJECTIVES (7.1)  Describe different type of isomerism for organic compounds  Describe organic reactions and chemical reagents 28  Personal Use Only. Not For Sale Isomerism Centre for Pre-University Studies ISOMERS Different compounds with the same molecular formula Constitutional Isomer Stereoisomer Isomers with the same molecular Isomers with the same molecular formula but different formula and atom connectivity, but atoms connectivity different spatial arrangement Chain Isomers Position Isomers Enantiomers Diastereomers Stereoisomers Stereoisomers that are non- that are not Functional Group superimposable mirror mirror images of Isomers images of each other each other 29  Personal Use Only. Not For Sale Isomerism Centre for Pre-University Studies Constitutional Isomer Isomers with the same molecular formula but different atoms connectivity Functional Group Isomers Chain Isomers Compounds with different carbon Compounds with different functional chains; straight or branched. Position Isomers groups. Example: Isomers with molecular Example: Isomers with molecular formula C4H10 Compounds with the same hydrocarbon formula C2H6O backbone but different position of the H H H H functional group. H H or Isomer H C C C C H or Example: Isomers with molecular formula Isomer 1 H C C O H OH 1 H H H H C4H9Cl H H Ethanol n-Butane H H H Cl H H H H H or Cl H C C C H Isomer 1 H C C C C H H C O C H O or or H H H H 1-Chlorobutane H H H H Isomer H C H Isomer 2 2 H Dimethyl Ether 2-Methylpropane H H Cl H or Isomer 2 H C C C C H Cl H H H H 2-Chlorobutane 30  Personal Use Only. Not For Sale Centre for Pre-University Studies Exercise 4  Draw the skeletal formulae for three chain isomers of n-hexane 31  Personal Use Only. Not For Sale 32 Isomerism Centre for Pre-University Studies Stereoisomer Enantiomers Compounds having the same molecular formula and Diastereomers same connectivity of atoms but different Stereoisomers arrangement in space around the carbon center. Stereoisomers that are that are non- (Different spatial arrangement) not mirror images of superimposable mirror each other images of each other non- superimposable Exist in compounds with: 1. Double bond The  bond in C=C prevents rotation along the bond axis due to the  parallel overlap of the unhybridized p orbitals of both C. 2. Ring structure The closed ring structure prevents the rotation of all connected C atoms.  Personal Use Only. Not For Sale 32 Isomerism Centre for Pre-University Studies Stereoisomer Enantiomers Compounds having the same molecular formula and Diastereomers same connectivity of atoms but different Stereoisomers arrangement in space around the carbon center. Stereoisomers that are that are non- (Different spatial arrangement) not mirror images of superimposable mirror each other images of each other non- superimposable 1. Double bond Compound The C atoms in without C-C bonds can rotate freely. These two double bond structures are the same. They are NOT 1,2-dichloroethane 1,2-dichloroethane isomers. The C atoms in C=C bonds cannot rotate. These two compounds have different Compound with double spatial arrangements for the Br and H bond atoms. They are geometric isomers. cis-1,2-dichloroethene trans-1,2-dichloroethene  Personal Use Only. Not For Sale 33 Isomerism Centre for Pre-University Studies Stereoisomer Enantiomers Compounds having the same molecular formula and Diastereomers same connectivity of atoms but different Stereoisomers arrangement in space around the carbon center. Stereoisomers that are that are non- (Different spatial arrangement) not mirror images of superimposable mirror each other images of each other non- superimposable 1. Double bond H3C CH3 H CH3 Isomer C C C C  An alkene shows cis-trans isomerism if H H H3C H each C atom of the double bond has 2 Melting different groups attached to it. point −139 ⁰C −106 ⁰C  Possess different physical and Less stable More stable chemical properties. Large alkyl groups are on Large alkyl groups are on Stability the same sides of the C=C, opposite sides of the C=C causing repulsion between bond, less repulsion between their electron clouds. their electron clouds.  Personal Use Only. Not For Sale 34 Isomerism Centre for Pre-University Studies Stereoisomer Enantiomers Compounds having the same molecular formula and Diastereomers same connectivity of atoms but different Stereoisomers arrangement in space around the carbon center. Stereoisomers that are that are non- (Different spatial arrangement) not mirror images of superimposable mirror each other images of each other non- superimposable 2. Ring Structure  In saturated ring compounds such as cycloalkanes, cis-trans isomerism arises due to restriction of bond rotation. cis-1,4-dimethylcyclohexane trans-1,4-dimethylcyclohexane  Personal Use Only. Not For Sale 35 Isomerism Centre for Pre-University Studies Stereoisomer Enantiomers Compounds having the same molecular formula and Diastereomers same connectivity of atoms but different Stereoisomers arrangement in space around the carbon centre. Stereoisomers that are that are non- (Different spatial arrangement) not mirror images of superimposable mirror each other images of each other non-superimposable  Exist in compounds with structures that are non-superimposable mirror reflection of each other. Structure of the Both structures are non- mirror image superimposable  Personal Use Only. Not For Sale 36 Isomerism Centre for Pre-University Studies Stereoisomer Enantiomers Compounds having the same molecular formula and Diastereomers same connectivity of atoms but different Stereoisomers arrangement in space around the carbon center. Stereoisomers that are that are non- (Different spatial arrangement) not mirror images of superimposable mirror each other images of each other non-superimposable  Chiral compound=consists chiral carbon will display optical stereoisomerism will have a non-superimposable mirror image molecule  Chiral carbon= carbon attached to four different atoms/groups Enantiomer 1 mirror Enantiomer 2  Personal Use Only. Not For Sale 37 Isomerism Centre for Pre-University Studies Stereoisomer Enantiomers Compounds having the same molecular formula and Diastereomers same connectivity of atoms but different Stereoisomers arrangement in space around the carbon centre. Stereoisomers that are that are non- (Different spatial arrangement) not mirror images of superimposable mirror each other images of each other non-superimposable  Achiral compound  Does not consist of chiral carbon  Will not display optical stereoisomerism H H I C C C I H I H H Br H H Br Achiral compounds  Personal Use Only. Not For Sale 38 Isomerism Centre for Pre-University Studies Stereoisomer Enantiomers Compounds having the same molecular formula and Diastereomers same connectivity of atoms but different Stereoisomers arrangement in space around the carbon centre. Stereoisomers that are that are non- (Different spatial arrangement) not mirror images of superimposable mirror each other images of each other non-superimposable  Example of achiral & chiral compounds H H H H Cl H H H H H O C C C H H O C C* C H H O C* C C H H H H H H H Cl H H propan-1-ol 2-chloropropan-1-ol 1-chloropropan-1-ol Achiral compound Chiral compound: Chiral compound: has an enantiomer has an enantiomer  Personal Use Only. Not For Sale 39 Isomerism Centre for Pre-University Studies Stereoisomer Enantiomers Compounds having the same molecular formula and Diastereomers same connectivity of atoms but different Stereoisomers arrangement in space around the carbon centre. Stereoisomers that are that are non- (Different spatial arrangement) not mirror images of superimposable mirror each other images of each other non-superimposable  Enantiomers are said to be optically active because they can rotate the plane of a plane-polarized light.  One isomer rotates clockwise, while the other isomer rotates anti-clockwise enantiomer 1 normal polaroid plane-polarized enantiomer 2 light filter light  Personal Use Only. Not For Sale Centre for Pre-University Studies Exercise 5  Draw structural formula of enantiomers of the following compounds. Use an asterisk (*) sign to indicate the chiral carbon 1. CH3CH2CH(OH)CH3 2. CH3CH2C(CH3) BrCH2CH2CH3 40  Personal Use Only. Not For Sale Organic Reagents Centre for Pre-University Studies Substance that causes a reaction to happen to organic compounds Types of Electrophile organic Nucleophile reagents Reagents that can accept Reagents that can an electron pair (Lewis's donate an electron pair Example: acids) from organic (Lewis’s bases) from Example: compounds. organic compounds. HBr Attracted to electron-rich Attracted to positively- OH regions in organic Cl2 charged region in organic compounds. CN compounds. H+ Radicals Anions, neutral NH3 Cations, neutral molecules that can be NO 2 + molecules with a lone pair of electrons H2O polarized or Lewis's AlCl3 Reagents that have an acids. unpaired valance electron. Very reactive  Cl 41  CH3  Personal Use Only. Not For Sale Centre for Pre-University Studies 42 Organic Reactions Addition Substitution 1 2 Reaction Reaction Two reactants become one Two reactants become two product. Unsaturated products. reactant become saturated product Types of organic reactions Elimination Rearrangement Reaction 4 3 Reaction Saturated reactant become One reactant become one unsaturated product. product  Personal Use Only. Not For Sale Centre for Pre-University Studies Organic Reactions Substitution 1 Two reactants become two products. Reaction  An atom or a group in a molecule is replaced by a nucleophile, or an electrophile, or a free radical.  Typical reactions of saturated compounds like alkanes, alkyl halides and aromatic compounds H H H H H C C H + NaOH H C C H + NaCl H Cl H OH Reactant Product 43  Personal Use Only. Not For Sale Centre for Pre-University Studies Organic Reactions Addition Two reactants become one product. Unsaturated 2 Reaction reactant become saturated product  2 molecules combine to form a single compound.  The attacking species may be a nucleophile, an electrophile or a free radical.  Typical reactions for compounds with a double or triple bond H H H H C C + Br Br H C C H H H Br Br Reactant Product 44  Personal Use Only. Not For Sale Centre for Pre-University Studies Organic Reactions Rearrangement 3 One reactant become one product Reaction  An atom or group moves from one atom to another within the molecule.  Rearrangements involving a group moving from a C atom to an adjacent C atom are referred to as 1,2-shifts.  Normally require catalysts. CH3 CH3 H3C C C CH2 H3C C C CH3 acid CH3 H CH3 Reactant Product 45  Personal Use Only. Not For Sale Centre for Pre-University Studies Organic Reactions Elimination 4 Saturated reactant become unsaturated product. Reaction  Involves removal of 2 atoms or groups from a molecule, usually from the adjacent C atom, forming a new double or triple bond.  The opposite of addition reactions. H H H H KOH H C C H C C + KBr + H2O in alcohol H Br H H Reactant Product  Personal Use Only. Not For Sale Centre for Pre-University Studies Organic Reaction Mechanism  Detailed description of the steps that took place during the transformation of reactants to form products.  Shows the sequence of bond breaking and forming. 46  Personal Use Only. Not For Sale Centre for Pre-University Studies Organic Reaction Mechanism Affected electron Shows only the pairs are shown Rules for writing reaction movement of electrons, as  or  or  mechanism NOT protons Half-head curved Full-head curved arrow is used arrow is used to to indicate the Arrow is drawn starting from the electron(s) indicate the movement of one origin to its new position where a new bond is movement of a pair electron (for to be formed: of electrons (for homolytic heterolytic reactions) reactions) Inorganic byproduct is sometimes shown as expelled material under the reaction arrow:  CH3Cl + NaOH CH3OH NaCl 47  Personal Use Only. Not For Sale Centre for Pre-University Studies Bond Breakage Heterolytic Homolytic Types of bond breakage Breakage Breakage Occurs in polar reaction Occurs in free radical reaction  Involves heterolytic breakage (heterolysis) of existing polar bond(s) and formation of new bond(s).  Involves transfer of electron pair(s).  Heterolysis of a bond to a carbon atom leads to either: i. a carbocation (positively-charged C atom). +  heterolys C Z is C+ + :Z ii. a carbanion (negatively-charged C atom).  + heterolys C Z is C: + Z+ 48  Personal Use Only. Not For Sale Centre for Pre-University Studies Bond Breakage Heterolytic Homolytic Types of bond breakage Breakage Breakage Occurs in polar reaction Occurs in free radical reaction  Involves homolytic breakage of existing bond(s).  Normally induced by application of high energy (heat or radiation).  Involves transfer of one electron.  Neutral reactive intermediate (free radical) is formed before the product. Cl Cl Cl + Cl 49  Personal Use Only. Not For Sale Centre for Pre-University Studies Thank You End of Learning Unit 7.1 50  Personal Use Only. Not For Sale Centre for Pre-University Studies PRK 1016 Learning Unit 7.2 51  Personal Use Only. Not For Sale Centre for Pre-University Studies LEARNING UNIT 7.2: ALIPHATIC HYDROCARBONS - ALKANE LEARNING OBJECTIVES (7.2)  Describe the source of alkane and the cracking process.  Describe the uses of hydrocarbons as fuels.  Name alkanes according to the IUPAC system  Describe the physical and chemical properties of alkanes. 52  Personal Use Only. Not For Sale Centre for Pre-University Studies Alkanes (Paraffin) General Info Sources of Alkane  A saturated hydrocarbons  Underground deposits of crude oil containing only the C-C and C- (petroleum) or natural gas. H single bonds.  Natural gas (mostly CH4), requires  All C atoms have sp3 little purification before use. hybridization.  Crude oil requires separation  Generally unreactive. process:  General formula: CnH2n+2  Step 1: Removal of water, acids & inorganics.  Step 2: Refined via fractional distillation.  Step 3: Less useful products converted to useful products via catalytic cracking process. 53  Personal Use Only. Not For Sale Centre for Pre-University Studies Fractional Distillation Number of refinery Temperature ˚C Carbons Fraction and Product gas 50˚C Gaseous methane, 2˚ > 1˚  3˚ C can be stabilized faster after the H atom is split from it since it has 3 other C atoms attached to it. 78  Thus, produced more stable 3˚carbon radical.  Personal Use Only. Not For Sale Centre for Pre-University Studies 1. Free Radical Substitution  Fluorination of alkane is a very violent reaction that breaks C-C and C-H bonds.  Iodination of alkane is a reversible process:  The percentage of major product formed is much larger than in chlorination. CH4 + I2 ⇄ CH3I + HI  To ensure enough production of iodoalkane, HI has to be continuously removed from the reaction mixture. 79  Personal Use Only. Not For Sale Centre for Pre-University Studies Exercise 2  Write the chemical equations to represent the steps for the chlorination of ethane. i. Chain Initiation: ii. Chain Propagation: iii. Chain Termination: 80  Personal Use Only. Not For Sale Centre for Pre-University Studies 2. Combustion of Alkane  Alkanes burn in excess oxygen to produce CO2, H2O (Products) and heat. CH4 + 2O2 CO2 + 2H2O ∆H = +ve C3H8 + 5O2 3CO2 + 4H2O ∆H = +ve  Complete combustion will produce a blue flame.  Bigger alkanes are harder to ignite because difficult for the molecules to move apart to turn into gas for combustion (greater Van der Waal).  Incomplete combustion of alkanes forms carbon particulates or CO gas.  Glowing carbon particulates turns the flame yellow.  Floating carbon particulates: soot. 81  Personal Use Only. Not For Sale Centre for Pre-University Studies 3. Oxidation of Alkane  Alkanes with 3˚ C atom are easily oxidized by oxidizing agent to form 3˚ alcohols. Oxidizing agent is a compound that accepts electrons from other reactant CH3 CH3 and can easily transfer KMnO4 oxygen in order to gain CH3 C H CH3 C OH electron CH3 CH3 isobutane tert-butyl alcohol methylpropane 2-methyl-2-propanol 82  Personal Use Only. Not For Sale Centre for Pre-University Studies 4. Pyrolysis of Alkane  Thermal decomposition of alkanes (without O2)  Lower alkanes decompose to form C & H2.  Higher alkanes decompose to form a mixture of alkanes & alkenes (cracking). C18H38 → C9H20 + C9H18  Catalytic cracking: forms mixture of shorter-chain alkanes & alkenes.  Hydrocracking: forms shorter-chain alkanes. 83  Personal Use Only. Not For Sale Centre for Pre-University Studies Thank You End of Learning Unit 7.2 84  Personal Use Only. Not For Sale Centre for Pre-University Studies PRK1016 Learning Unit 7.3 85  Personal Use Only. Not For Sale Centre for Pre-University Studies LEARNING UNIT 7.3: ALIPHATIC HYDROCARBONS - ALKENE LEARNING OBJECTIVES (7.3)  Name alkenes based on the IUPAC system.  Describe the isomerism of alkenes.  Describe the stability of alkenes.  Describe the chemical reactions of alkenes. 86  Personal Use Only. Not For Sale Centre for Pre-University Studies Alkene (Olefin) H H C C H H General Info  An unsaturated organic compound  Contains the C=C functional group  Naming ends with the suffix –ene  General formula: CnH2n  Carbons in the C=C bond have sp2 hybridization.  All 3 bonding pairs are arranged in a trigonal planar geometry around the C atom with a bond angle of 120˚.  The double bond (σ and π bond) prevents rotation along the C=C bond axis, leads to geometric isomerism.  The C=C bond is also a region of high electron density: C=C bond have 4 bonding electrons.  The C=C bond region easily attracts electrophiles. 87  Personal Use Only. Not For Sale Centre for Pre-University Studies IUPAC Nomenclature 1. The longest chain must contain the C=C.  Numbering must start from the end which gives the lowest number possible to the double bond. 2. Each substituent is listed with a location number.  Prioritize the functional group to has the lowest number possible H H H H H H H H H C H H C C C C C C H H C C C C C C H H H H H H H H H H H H H 5-Methylhex-2-ene Hex-2-ene NOT Hex-4-ene NOT 2-Methylhex-4-ene 88  Personal Use Only. Not For Sale Centre for Pre-University Studies IUPAC Nomenclature 3. If the double bond is located at equal distance from both ends, numbering starts from the end that gives the lowest location number to the first substituent. Br 2,5-dimethyloct-4-ene 2-bromo-4-methylhex-3-ene NOT NOT 4,7-dimethyloct-4-ene 5-bromo-3-methylhex-3-ene 89  Personal Use Only. Not For Sale Centre for Pre-University Studies IUPAC Nomenclature 4. Multiple C=C bonds:- Number of C=C IUPAC (Suffix) Example 2 Diene Hexa-2,4-diene 3 Triene Octa-2,4,6-triene 4 Tetraene Cycloocta-1,3,5,7-tetraene 90  Personal Use Only. Not For Sale Centre for Pre-University Studies IUPAC Nomenclature 5. For cyclic alkenes consist of ONE C=C :-  the C=C is always between C1 & C2. No need to mention the position number of C=C in the name.  Numbering direction must give the lowest number to the first substituent. 1,6-dimethylcyclohexene 5-ethyl-1-methylcyclohexene NOT NOT 2,3-dimethylcyclohexene 4-ethyl-2-methylcyclohexene 91  Personal Use Only. Not For Sale Centre for Pre-University Studies 92 IUPAC Nomenclature Isomers in Alkene Constitutional Geometric Isomers Isomers  Alkenes may show cis-trans isomerism.  Chain isomers:  Due to the rotation restriction of the C=C bond. C6H12  Geometric isomers have different physical 2,3-dimethylbut-2-ene 2-methylpent-2-ene properties but the same chemical properties. H3C CH3 H3C H H2 Isomer of C C C C CH3-CH=CH2 C3 H6 C but-2-ene propene H2C CH2 H H H CH3  Functional group isomers: cyclopropane cis-but-2-ene trans-but-2-ene Melting point (˚C) –139 –106  Personal Use Only. Not For Sale Centre for Pre-University Studies IUPAC Nomenclature Isomers in Alkene Geometric Isomers  Used when there are 3 or 4 different atoms / groups attached to the C=C.  E- (entgegen: opposite) - Higher priority atoms (bigger atomic mass) on opposite sides.  Z- (zusammen: together) - Higher priority atoms (bigger atomic mass) on the same side. Br F Br Cl C C C C I Cl I F Z-1-bromo-2-chloro-2-fluoro-1- E-1-bromo-2-chloro-2-fluoro-1- iodoethene iodoethene 93  Personal Use Only. Not For Sale Centre for Pre-University Studies IUPAC Nomenclature Isomers in Alkene Geometric Isomers  All cis-trans isomers are E-Z isomers, but not all E-Z isomers are cis-trans isomers.  In compounds with more than one C=C bonds, each C=C bond can form separate geometric isomer. CH3 H3C H H H H H3C C C H3C C C C C H H H C C CH3 C C C C H H H H H CH3 cis,cis-hexa-2,4-diene cis,trans-hexa-2,4-diene trans,trans-hexa-2,4-diene Or Or Or (Z,Z)-hexa-2,4-diene (Z,E)-hexa-2,4-diene (E,E)-hexa-2,4-diene 94  Personal Use Only. Not For Sale Centre for Pre-University Studies Stability of Alkanes  The more highly-substituted double bonds are more stable. Saytzeff (Zaitsev)  The trans- isomer is more stable than the cis- isomer. Rule  The larger alkyl groups are on opposite sides of the double bond: with less steric hindrance. R R R H RCH=CHR , C C > C C > R2C=CH2 > RCH=CH2 > H2C=CH2 R R R R 95  Personal Use Only. Not For Sale Centre for Pre-University Studies Reactivity - Electrophilic Addition  The C=C is more reactive compared to the C-C bonds in alkanes.  The C=C bond in an alkene is an electron-rich RECAP - Electrophile region. Reagents that can accept Example:  Electrophiles are attracted to this C=C region. an electron pair (Lewis's  The heterolytic fission of the  bond leads to acids) from organic HBr compounds. the formation of two new  bonds. Cl2 Attracted to electron-rich  Electrophilic addition reaction occurs. regions in organic H+ compounds. NO2+  Since the addition reaction involves an Cations, neutral electrophile to be added to the C=C bond, the molecules that can be AlCl3 polarized or Lewis's reaction is called Electrophilic Addition. acids. 96  Personal Use Only. Not For Sale Centre for Pre-University Studies Electrophilic Addition E E Y C C + E+ C+ C C C Y  The electrophile gains 2 electrons from a double bond C atom and forms a covalent bond.  The adjacent C atom loses its electron and becomes a carbocation.  A nucleophile is attracted to the carbocation and forms a new covalent bond. 97  Personal Use Only. Not For Sale Centre for Pre-University Studies 98 Reactions in Alkene 1. Catalytic 3. Addition of Hydrogenation 5. Oxidative Cleavage Hydrogen Halide 2. Halogenation 4. Oxidation 6. Polymerisation  Personal Use Only. Not For Sale Centre for Pre-University Studies 99 Reactions in Alkene 1. Catalytic  Alkenes do not react with H2 under normal temperature & pressure. Hydrogenation  However, in the presence of Pt or Ni catalyst at 200˚C, alkenes undergo addition reaction with H2 to form alkanes.  Alkenes are dissolved in ethanol with the metal catalyst before being exposed to H2 under pressure. P CH3CH2CH=CH2 + H2t CH3CH2CH2CH3 but-1-ene butane  Mechanism: syn addition H C C H------H C C H------H C C C C H H + H surface of pt/Ni catalyst  Personal Use Only. Not For Sale Centre for Pre-University Studies 100 Reactions in Alkene i. Reaction of alkene with halogen gas  Alkenes react with Cl2 and Br2 (in CCl4) instantly at room temperature, even in the dark.  The halogen atoms are added to the alkene to form vicinal 2. Halogenation dihalides. H H H H CH3CH=CHCH3 + Cl2 H C C C C H H Cl Cl H but-2-ene 2,3-dichlorobutane  Personal Use Only. Not For Sale Centre for Pre-University Studies 101 Reactions in Alkene Mechanism: 1. As Cl2 molecule approaches the  electrons, Cl2 molecule becomes polarized (induced polarisation).This weakens the Cl-Cl bond, causing it to break heterolytically. 2. The Cl ion formed attacks one of the C atom of the chloronium ion and 2. Halogenation produce vicinal dihalides product. Cl+ Cl Cl C C + ClCl C C + Cl C C chloronium chloride Vicinal dichloride ion ion  Personal Use Only. Not For Sale Centre for Pre-University Studies 102 Reactions in Alkene ii.Reaction of alkene with aqueous halogen  Halogenation reaction of alkene using halogens in water will form alcohol with a halide substituent.  Bromine water is an orange-brown solution. When mixed with an 2. Halogenation alkene, the solution becomes colourless.  The major product formed when alkene is reacted with aqueous Br 2 is 2-bromoethanol but 1,2-dibromoethane is also formed as a minor product. OH Br H H C C + Br2 + H2O H C C H + HBr H H H H 2-bromoethanol  Personal Use Only. Not For Sale Centre for Pre-University Studies Exercise 1  Draw the skeletal formula for compound X, Y and Z. H2, Pt Br2, H2O X Z Br2 Y 103  Personal Use Only. Not For Sale Centre for Pre-University Studies 104 Reactions in Alkene i. Symmetrical alkene 3. Addition of  Hydrogen halide, HX, adds readily to the C=C bond of Hydrogen Halide symmetrical alkene to form alkyl halide product H Br H H C C + HBr H C C H H H H H Ethene 2-bromobutane  Personal Use Only. Not For Sale Centre for Pre-University Studies 105 Reactions in Alkene 3. Addition of Mechanism: Hydrogen Halide Step 1 The slightly positive H in HX will receive an electron pair from the π bond in alkene. HX breaks heterolytically and forms the nucleophile X –. Step 2 The active (unstable) carbocation stabilizes itself by combining with the remaining halide ion (nucleophile) to form alkyl halide. slow fast endothermic H exothermic H reaction reaction C C + HX C+ C + X C C Step 1 Step 2 X carbocation halide ion  Personal Use Only. Not For Sale Centre for Pre-University Studies 106 Reactions in Alkene i. Asymmetrical alkene 3. Addition of  The addition of HX to an asymmetrical alkene could occur in 2 Hydrogen Halide ways, producing a major and a minor product.  Based on Markovnikov’s Rule:  To produce a major product, the H atom of HX need to be added to the C atom of the double bond that has the greater no. of H atoms.  Personal Use Only. Not For Sale Centre for Pre-University Studies 3. Addition of Hydrogen Halide Markovnikov’s Rule Mechanism 2˚ carbocation H H H H H H more stable H C C+ C H H C C C H H H H Br H H H H faster 2-bromopropane Br major product + H-Br +  H C C C H H slower H H H H H H 1˚ carbocation H C C C+ H H C C C H less stable H H H H Br 1-bromopropane Br minor product  The electrophile (H+) will attach itself to the C atom in a C=C bond that leads to formation of a more stable carbocation as an intermediate.  The nucleophile (X-) will then form a bond with the carbocation and forms the major product. 107  Personal Use Only. Not For Sale Centre for Pre-University Studies Exercise 2  Draw the skeletal formulae for major and minor product for reaction below: HI Major product + Minor product 108  Personal Use Only. Not For Sale Centre for Pre-University Studies 109 Reactions in Alkene  Oxidation of alkene with cold acidified manganate(VII) solution will produce alkanediol or glycol.  The purple colour of manganate(VII) will be decolourised OH OH 4. Oxidation H H Cold KMnO4 C C H C C H H H dilute H+ H H ethane-1,2-diol  Personal Use Only. Not For Sale Centre for Pre-University Studies 110 Reactions in Alkene  Hot, concentrated acidified manganate(VII) oxidizes alkenes to 5. Oxidative Cleavage glycols, then cleaves the glycols.  Ketones & aldehydes will be formed.  The aldehydes are further oxidized to form carboxylic acids H OH O C O C OH OH R’ R’ R R’ aldehyde Hot KMnO4 carboxylic C C R C C H acid + R H H+ R R’ R C O glycol R ketone  Personal Use Only. Not For Sale Centre for Pre-University Studies 111 Reactions in Alkene  When smaller alkene units (monomers) go through addition reaction, a polymer is formed.  Common catalyst used in polymerization reactions is Ziegler- 6. Polymerisation Natta, an organoaluminum compound containing transition metal. R R R R R R C C + C C + C C +… R R R R R R ethene monomers polymerisation R R C C polyethene polymer R R n  Personal Use Only. Not For Sale Centre for Pre-University Studies 112 Reactions in Alkene  Example of other polymers and their monomers: Monomer Polymer Some of the usage CH3 H Polypropene (PP) Turned into fibers to make ropes, sacks & carpets. Propene C C H H Polychloroethene Used in plastic windows, or electrical cable insulation, Cl H polyvinyl chloride footwear & clothing. Chloroethene C C (PVC) 6. Polymerisation H H Polytetrafluoroethene Used in non-stick kitchen or Teflon (brand utensils. name) F F Tetrafluoroethene C C F F  Personal Use Only. Not For Sale Centre for Pre-University Studies Thank You End of Learning Unit 7.3 113  Personal Use Only. Not For Sale Centre for Pre-University Studies PRP 1016 Learning Unit 7.4 114  Personal Use Only. Not For Sale Centre for Pre-University Studies LEARNING UNIT 7.4: AROMATIC COMPOUND - BENZENE LEARNING OBJECTIVES (7.4)  Describe the ring structure of benzene.  Name aromatic compound based on the IUPAC system.  Describe the reactions of aromatic compounds. 115  Personal Use Only. Not For Sale Centre for Pre-University Studies Aromatic (Arene)  Aromatic compound contains the benzene ring functional group.  Called aromatics due to the aroma (fragrant) produced from most of aromatic compounds founds in plants.  Aromatics now refer to benzene & compounds that resemble benzene in their chemical properties. OH O 2-Phenylethanol 4-Methoxytoluene Rose Ylang ylang 116  Personal Use Only. Not For Sale Centre for Pre-University Studies Modern Theory on the Structure of Benzene  Each C atom is attached to 1 H atom and 2 other H H C atoms. C C  Each C atom has sp2 hybridization. H C C H  The C-C-C bond angle is 120˚.  The C atom also has 1 unhybridized p orbital. C C H  The 6 unhybridized p orbital overlap to form a H circular  bond on top & below the ring.  bond from sp2 hybridisation  Each electron in the 6 unhybridized p orbitals will unhybridised p orbital delocalized over the ring  bond.  overlap of unhybridised p orbitals 117  Personal Use Only. Not For Sale Centre for Pre-University Studies Modern Theory on the Structure of Benzene H H C H C C C C H C H H  Due to the  bond forming over 6 C atoms instead of between 2 C atoms like in alkenes, the ring structure is very stable.  The C-C bonds are neither single nor double bonds.  C-C bond length: 1.48 Å  C=C bond length: 1.34 Å  C-C bond length in benzene: 1.397 Å 118  Personal Use Only. Not For Sale Centre for Pre-University Studies Stability of Benzene  Benzene has C=C bonds, like alkenes, which is supposed to make it very reactive towards addition of electrophile.  Surprisingly, benzene react via substitution, like alkane.  C6H6 + Br2 → C6H5Br + HBr  C6H6 + Br2 → C6H6Br2  Benzene is stable and unreactive. Reagent Cyclohexene Benzene Br2/CCl4 (in the dark) Quick addition No reaction KMnO4 dil./25C Quick oxidation No reaction 119  Personal Use Only. Not For Sale Centre for Pre-University Studies IUPAC Nomenc