1 Introduction to Organic Chemistry (What are Things Made of?) Dr. Kendrew K. W. Mak Department of Chemistry The Chinese University of Hong Kong IJSO Training (Phase 2)

2 Roles of Organic Chemistry in Daily Life Organic compounds ( 有機化合物 ) can be found in: Detergents ( 清潔劑 )Pesticides ( 農藥 / 殺蟲劑 ) Gasoline ( 汽油 ) / Fuels ( 燃料 ) Paints Dyes ( 染料 ) Medicines Computers / Communication products Living organisms Food Plastics / polymers ( 塑膠 / 聚合物 ) and a lot more ……

3 Classical Definition Compounds obtained or derived from living organisms Modern Definition Compounds that are made up of carbon atoms. What is Organic Chemistry ( 有機化學 ) About 13 million organic compounds are known today. About 100,000 new ones discovered every year. There are only 200,000 to 300,000 known inorganic compounds (those are made up of elements other than carbon)

4 Vanillin ( 香草醛 ) Tetramethylpyrazine ( 川芎嗪 ) Interesting Organic Compounds – Compounds having favorable aromas

5 Organic Compounds Natural Organic Compounds Proteins ( 蛋白質 ), enzyme ( 酵 ), vitamins ( 維生素 ), lipids ( 脂質 ), carbohydrates ( 碳水化合物 ), nucleic acid ( 核酸 ) …… Synthetic (Man-made Compounds) Synthetic fabrics ( 合成織品 ), plastics ( 塑膠 ), synthetic rubber ( 合成 橡膠 ), medicine ( 藥物 ), adhesives ( 黏合劑 ), photographic film ( 攝影 菲林 ) ……

6 Diversified Structures Simple Complex

7 Hydrocarbons – Contain only Carbon and Hydrogen Atoms Organic compounds that contain only carbon and hydrogen are called hydrocarbons ( 碳氫化合物 ). Hydrocarbons differ from one another in the number of carbon atoms present in one molecule, and the ways that they are bonded together. Methane ( 甲烷 ) has one carbon atom, and octane ( 辛烷 ) has eight. Polyethylene ( 聚乙烯 ) contains hundreds to thousands of carbon and hydrogen atoms in each molecules. Methane (CH 4 )Octane (C 8 H 18 )Polyethene

8 Molecular Sizes and Properties Name Molecular Formula Melting Point (°C)Boiling Point (°C) Physical State (At 20°C) MethaneCH Gas EthaneC2H6C2H Gas PropaneC3H8C3H Gas ButaneC 4 H Gas PentaneC 5 H Liquid HexaneC 6 H Liquid HeptaneC 7 H Liquid OctaneC 8 H Liquid NonaneC 9 H Liquid DecaneC 10 H Liquid Physical Properties of Some Alkanes ( 烷烴 )

9 Hydrocarbons also differ from one another in the way the carbon atoms bonded to each other. Structural Isomers of Hydrocarbons Straight chain ( 直鏈 ) Branched chains ( 支鏈 ) n-Pentane, C 5 H 12 iso-Pentane, C 5 H 12 neo-Pentane, C 5 H 12

10 Structural Isomers of Hydrocarbons Boiling Point. 30°C 10°C 36°C The number of possible structural isomers ( 異構體 ) of a chemical formula increases rapidly as the number of carbon atoms increases. C 5 H 12 3 isomers C 8 H isomers C 20 H ,316 isomers n-Pentane, C 5 H 12 iso-Pentane, C 5 H 12 neo-Pentane, C 5 H 12

11 Conformers – Same Molecule with Different Spatial Orientations

12 Petroleum ( 石油 ) – Major Source of Hydrocarbon Petroleum (also known as crude oil) is a complex mixture consisting mainly of alkanes. It corresponds to the fossil ( 化石 ) remains of microscopic animals that lived in the seas in ancient times. Fractional distillation ( 分餾 )

13 Alkane – The Simplest Form of Hydrocarbon Methane (CH 4 ) Natural Gas Biogas (marsh gas) Butane ( 丁烷 ) (C 4 H 10 ) Liquefied petroleum gas ( 液化石油氣 )(LPG) Lighter gas

14 Alkane – The Simplest Form of Hydrocarbon Octane Number ( 辛烷值 ) Heptane 2,2,4-Trimethylpentane

15 Boosting Up the Octane Number Anti-Knocking Agent ( 抗震劑 ) Anti-Knocking Agent ( 抗震劑 ) Tetramethyl lead ( 四甲基鉛 ), Pb(CH 3 ) 4 Tetraethyl lead ( 四乙基鉛 ), Pb(C 2 H 5 ) 4 Toxic – leukemia ( 白血病 ) Cause air pollution - Produce smog ( 煙霧 )

16 Saturated and Unsaturated Hydrocarbons Saturated Hydrocarbons – contain single bonds only Unsaturated Hydrocarbons – contain multiple bonds n-Butane, C 4 H 10 But-2-ene, C 4 H 8 Saturated hydrocarbon ( 飽和碳氫化合物 ) Unsaturated hydrocarbon ( 不飽和碳氫化合物 ) ( 丁烷 ) ( 丁 -2- 烯 )

17 Alkenes – Hydrocarbons with C=C Double Bonds Ethene/Ethylene ( 乙烯 ) (C 2 H 4 ) – The simplest alkene ( 烯 ) Use: Making polymer (polythene) A plant hormone (triggers fruit ripening) Beta-carotene is the precursor molecule to vitamin A ( 胡蘿蔔素 )

18 Alkenes – Hydrocarbons with C=C Double Bonds Polymerization ( 聚合作用 )

19 Sigma (  ) Bond and Pi (  ) Bond Compounds with double covalent bond Ethene (CH 2 =CH 2 ) Double covalent bond = 1  bond + 1  bond Pi (  ) – side-to-side overlap 121.7° 116.6° 1.33Å A double bond consists of one σ bond and one  bond 1.08Å CC H HH H

20 Geometrical Isomers ( 幾何異構體 ) of Alkene ( 順 - 丁 -2- 烯 ) ( 反 - 丁 -2- 烯 )

21 C=C Double Bonds: Absorption of Light UV-C:below 280 nm UV-B:280 nm – 320 nm UV-A:320 nm – 400 nm Visible light:400 nm – 700 nm 1 nm = m Compound max (nm)  (M -1 cm -1 ) 16515, , , , , ,000

22 Sunscreens ( 防曬霜 ) not very soluble in oily skin lotions

23 1 nm = m tomatoes, watermelon, pink grapefruit (red) carrots, apricots, sweet potatoes (orange)  -carotene ( 胡蘿蔔素 ) max = 455nm lycopene ( 番茄紅素 ) max = 474nm C=C Double Bonds: Absorption of Light

24 Benzene and Aromatic Compounds The electrons of the double bonds in benzene ( 苯 ) are not confined between any two carbon atoms. These electrons are able to move freely around the ring. Toluene Naphthalene 1,4-Dichlorobenzene some common aromatic compounds ( 芳香族化合物 ):

25 The Delocalization of Electrons in Benzene Resonance structures ( 共振結構 ) of benzene III

26 The Delocalization of Electrons in Benzene A compound with delocalized electrons is more stable than it would be if all of its electrons were localized. The extra stability a compound gains from having delocalized electrons is called delocalization energy ( 離域能 ) or resonance energy ( 共振能 ). benzene + 3H 2 “cyclohexatriene” + 3H 2 cyclohexane  H° = kcal/mol (-359kJ/mol)  H° = kcal/mol (-208kJ/mol) 36 kcal/mol (151kJ/mol) Potential energy

27 Delocalization ( 離域作用 ) – Two More Examples Delocalization in the carbonate ion Bonding in ethanoic acid and the ethanoate ion

28 Organic Molecules are Classified by Functional Groups Ethane (C 2 H 6 ) Ethanol (C 2 H 5 OH) Ethylamine (C 2 H 5 NH 2 ) Boiling point = - 88°C A gas at room temperature Insoluble in water. Boiling point = + 78°C A liquid at room temperature Soluble in water For making alcoholic beverages A corrosive ( 腐蝕性 ), pungent ( 刺激性 ), highly toxic gas

29 Organic Molecules are Classified by Functional Groups Function group ( 官能基 ) is defined as a combination of atoms that behave as a unit. General Structure NameClass Hydroxyl groupAlcohols Phenolic groupPhenols Ether groupEthers Amine groupAmines Ketone groupKetones Aldehyde group Aldehydes Amide groupAmides Carboxyl groupCarboxylic acids Ester groupEsters

30 Alcohols Contain the Hydroxyl Group Alcohols are organic molecules in which a hydroxyl group is bonded to a saturated carbon. Methanol ( 甲醇 ) Isopropanol ( 異丙醇 ) Making methylated spirit Fuel for racing car Rubbing alcohol

31 Alcohols Contain the Hydroxyl Group Ethanol Fermentation ( 發酵作用 )

32 Transformation of Function Groups Conversion of alkenes to alcohols (hydration 水合作用 ) An acid-catalyzed reaction

33 Interconversion of Alcohols and Alkyl Halides bromomethane

34 Some Common Halogenated Hydrocarbons FormulaCommon nameIUPAC nameSome important uses CH 3 ClMethyl chloride Derived from methane ChloromethaneRefrigerant; manufacture of silicones, methyl cellulose, and synthetic rubber CH 2 Cl 2 Methylene chlorideDichloromethaneLaboratory and industrial solvent CHCl 3 ChloroformTrichloromethaneIndustrial solvent CCl 4 Carbon tetrachlorideTetrachloromethane(see text) CBrF 3 Halon-1301BromotrifluoromethaneFire extinguisher systems CCl 2 F 2 CFC-12DichlorodifluoromethaneRefrigerant CH 3 CH 2 ClEthyl chloride Derived form ethane ChloroethaneLocal anesthetic ClCH 2 CH 2 ClEthylene dichloride1,2-dichloroethaneSolvent for rubber CCl 3 CH 3 Methylchloroform1,1,1-trichloroethaneSolvent for cleaning computer chips and molds for shaping plastics Some Halogenated Hydrocarbons

35 Reactions of Alcohols and Halogenated Hydrocarbons Diethyl ether Diethyl ether was used as an anesthetic ( 麻醉劑 ) starting from mid-19 th century. A commonly used laboratory solvent. MTBE as fuel additive ( 燃料添加劑 ) Methyl tert-butyl ether (MTBE) It burns very completely and reduces the emission of carbon monoxide. Very high octane rating (116), replace aromatic hydrocarbons Very strong odor, sickening to some people. Decompose very slowly in nature, polluting the environment.

36 Different Types of Isomers Isomers Structural Isomers ( 結構異構體 ) (Different bonding) Stereoisomers ( 立體異構體 ) (Different shapes) Positional Isomers 位置異構體 Hydrocarbon Chain Isomers 碳氫鏈異構體 Functional Group Isomers 官能基異構體 Geometric Isomers 幾何異構體 Enantiomers (Optical Isomers) 對映異構體 ( 旋光異構體 )

37 Different Types of Isomers Positional Isomers Hydrocarbon Chain Isomers Functional Group Isomers

38 Geometric Isomers Enantiomers (Optical Isomers) (See next page …… ) Different Types of Isomers

39 Asymmetric Carbon ( 不對稱碳原子 ) – is a carbon atom that bonded to four different groups An asymmetric carbon can be known as a chiral ( 手性 ) center Optical Isomers and Chiral Compounds

40 Conversion of Alcohols to Aldehydes ( 醛 ) The aldehyde group Oxidation Reaction ( 氧化反應 ) Very toxic Less toxic

41 Some Common Aldehydes Formaldehyde ( 甲醛 ) Large amounts of formaldehyde are used for producing adhesives for making plywood ( 夾板 ). Embalming ( 防腐 )

42 Some Common Aldehydes AldehydesStructureFood that contain the aldehydes Vanillin ( 香草醛 ) Vanilla Ice-cream Benzaldehyde ( 苯醛 ) Almond Cinnamaldehyde ( 肉桂醛 ) Cinnamon

43 From Wine to Vinegar Carboxyl group White vinegar – 5% acetic acid solution

44 Carboxylic Acids Found in Foods AHAs Alpha-hydroxy acids AHAs contain a hydroxyl group (-OH) bonded to the first carbon atom attached to the –COOH group. Tartaric acid Malic acidLactic acid Citric acid

45 Reactions of Carboxylic Acids with Alcohols ester linkage ( 酯鍵合 )

46 Some Esters ( 酯 ) and Their Odors NameStructureOdor Ethyl formateHCOO—CH 2 CH 3 Rum Isobutyl formateHCOO—CH 2 CH(CH 3 ) 2 raspberry Ethyl acetateCH 3 COO—CH 2 CH 3 Floral Propy acetateCH 3 COO—CH 2 CH 2 CH 3 Pear Pentyl acetateCH 3 COO—CH 2 CH 2 CH 2 CH 2 CH 3 Banana Isopentyl acetateCH 3 COO—CH 2 CH 2 CH(CH 3 ) 2 Banana Octyl acetateCH 3 COO— CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Orange Benzyl acetateCH 3 COO—CH 2 C 6 H 5 Jasmine Isobutyl propionateCH 3 CH 2 COO—CH 2 CH(CH 3 ) 2 Apple Methyl butyrateCH 3 CH 2 CH 2 COO—CH 3 Rum Ethyl butyrateCH 3 CH 2 CH 2 COO—CH 2 CH 3 Pineapple Butyl butyrateCH 3 CH 2 CH 2 COO—CH 2 CH 2 CH 2 CH 3 Pineapple Amyl butyrateCH 3 CH 2 CH 2 COO—CH 2 CH 2 CH 2 CH 2 CH 3 Apricot Isoamyl pentanoateCH 3 CH 2 CH 2 CH 2 COO—CH 2 CH 2 CH(CH 3 ) 2 Apple

47 More About Oxidation and Reduction Reactions Oxidation (in organic chemistry) – often refers to: gaining oxygen atoms (+ O) losing hydrogen atoms (- H) Oxidation (in organic chemistry) – often refers to: gaining oxygen atoms (+ O) losing hydrogen atoms (- H) oxidation – 氧化作用 ; reduction – 還原作用

48 More About Oxidation and Reduction Reactions Reduction (in organic chemistry) – often refers to: losing oxygen atoms (- O) gaining hydrogen atoms (+ H) Reduction (in organic chemistry) – often refers to: losing oxygen atoms (- O) gaining hydrogen atoms (+ H)

49 More About Oxidation and Reduction Reactions

50 Amines ( 胺 ) and Amides ( 酰胺 ) Amines – substances with “fishy” smell. Amides – linking the amino acids in proteins

51 Organic Chemistry in Daily Life Polymers & Plastics ( 聚合物及塑膠 ) Detergents ( 清潔劑 )

52 What is Polymer? Polymer – substances that contain very long molecular chains and have the same structural unit repeating over and over again. Examples of natural polymers – cotton, silk and rubber. cottonclothes made from silk tire made of rubber

53 Silk – natural protein fiber Cotton – mainly composed of cellulose ( 纖維素 ). Natural polymers cellulose  - D -glucose alanine glycine serine Rubber – formed from the polymerization of isoprene ( 異戊二烯 )

54 Addition Polymerization ( 加成聚合作用 ) The two major ways of making polymers: addition polymerization and condensation polymerization. Addition polymerization – joining the monomers together without losing any small molecule or atom. Examples are Polystyrene (PS) Polythene (PE) addition polymerization addition polymerization Monomer ( 單體 ) –low molecular weight compound that can be connected together to give a polymer ( 聚乙烯 ) ( 聚苯乙烯 )

55 Condensation polymers are formed by condensation ( 縮合作用 ) reactions, in which small molecules such as water or hydrogen chloride are eliminated in the polymerization process. Examples are Polyethylene terephthalate (PET) Nylon + + Condensation Polymerization ( 縮合聚合作用 ) “ A polyester – 聚酯 ” ( 聚對苯二甲酸乙二酯 )

56 Thermoplastics ( 熱塑性塑膠 ) Thermoplastics The polymer molecules are held together by the weak intermolecular van Der Waals forces ( 范德華力 ). At elevated temperature, it is easy to "melt" these bonds and the molecular chains can slide past one another easily. These polymers can be soften or melted by heating, and can be remolded into different forms. The chain can be stretched, which cause them to flow pass each other, When released, the polymer will not return to its original form. original form polymer strands have little tendency to return to its original form

57 Thermosetting Plastics These are three-dimensional polymers which are highly cross-linked by strong chemical bonds such as covalent bonds. Thermosetting polymers are “set” or “polymerized” through chemical reactions to form the cross-links ( 交 鍵 ). Once the chemical reaction or polymerization is complete, the polymer becomes a hard, infusible, insoluble material which cannot be softened, melted or molded. Thermosetting Plastics ( 熱固性塑膠 )

58 Soaps and Detergents ( 肥皂及清潔劑 ) Soap cleans by: Decreasing water ’ s surface tension, making it a better wetting agent; Converting greasy and oily dirt into small particles that become dispersed in the soapy water; Keeping the grease particles in suspension ( 懸浮狀態 ), preventing them getting together and stick back to the clean surface. Water is a poor cleaning agent: Water has high surface tension ( 表面張力 ). It tends to form beads and droplets, and does not wet substances very well. It cannot dissolve greasy dirt effectively.

59 The Soap Molecule Na + or K + Hydrophobic ( 疏水性 ) tail is attracted to oily, greasy, hydrocarbon-like substances. Hydrophilic ( 親水性 ) head is attracted to water molecules.

60 Breaking the Surface Tension

61 Removing the Greasy Dirt The particles (micelles) repel each other, forming many tiny suspended droplets. The soap molecules embed the hydrophobic tails into the greasy dirt and leave it off the surface.

62 Making of Soap : Saponification of Triglyceride Triglycerides are the principal constituents of animal fats and vegetable oils. R, R ’ and R ” : Straight (unbranched) hydrocarbon chains. saponification – 皂化作用 ; triglyceride – 甘油三酸酯

63 Soap and Hard Water ( 硬水 ) Hard water: high mineral content rich in calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ ) Soap forms insoluble precipitates (soap curd) with hard water. It reduces the cleaning power of soap. precipitate – 沉澱物

64 Soapless Detergent ( 非皂性清潔劑 ) Replace the anionic carboxylate group with a sulfonate group. Alkyl sulfonates do not form insoluble salts in hard water. Sodium lauryl sulfate (SLS) or sodium dodecyl sulfate (SDS) R = alkyl group Sodium alkylbenzenesulfonate