Atoms and Molecules by k4wp82i

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									Introduction to Organic
Chemistry
(What are Things Made of?)

    IJSO Training (Phase 2)


           Dr. Kendrew K. W. Mak
          Department of Chemistry
     The Chinese University of Hong Kong
                                           1
  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    Living organisms
 products
 Food                         Plastics / polymers (塑膠 / 聚合物)

                                            and a lot more ……




                                                                2
  What is Organic Chemistry (有機化學)

Classical Definition

   Compounds obtained or derived from living organisms


Modern Definition

   Compounds that are made up of carbon atoms.



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)
                                                              3
Interesting Organic Compounds –
Compounds having favorable aromas
                         O    H




                                O
                             OH  CH 3

                        Vanillin (香草醛)



                                  N


                                  N

                        Tetramethylpyrazine
                             (川芎嗪)
                                          4
  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) ……




                                                                5
   Diversified Structures

       O              H H H                            O
                    H C C O                           O
                                                           O
H 3C       CH 3       H H           O   NH   O                 OH

                    (CH 3 CH 2OH)                O
                                         OH
                                                     HO        O
        OH                                           O  OO
              O                                                O
  HO                 OH
   HO
              OH
               O         OH
                     O
                              OH
                    OH
                                                 Complex

           Simple
                                                                    6
   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 (CH4)    Octane (C8H18)                  Polyethene
                                                                7
  Molecular Sizes and Properties
Physical Properties of Some Alkanes (烷烴)

                Molecular                                           Physical State
     Name                   Melting Point (°C) Boiling Point (°C)
                Formula                                               (At 20°C)

   Methane        CH4             -182                -164               Gas

    Ethane        C2H6            -183                -89                Gas

    Propane       C3H8            -190                -42                Gas

    Butane       C4H10            -138                 -1                Gas

    Pentane      C5H12            -130                 36              Liquid

    Hexane       C6H14             -95                 69              Liquid

   Heptane       C7H16             -91                 98              Liquid

    Octane       C8H18             -57                125              Liquid

    Nonane       C9H20             -51                151              Liquid

    Decane       C10H22            -30                174              Liquid

                                                                                     8
       Structural Isomers of Hydrocarbons
    Hydrocarbons also differ from one another in the way the
    carbon atoms bonded to each other.

                                          H                         H       HH       H
                                                                        C        C
H        HH         HH        H       H   C     H
                                                                    H       C        H
     C         C          C       H       C         H       H       H                H

H         C           C       H       C         C       C       H       C        C
                                           H
     H         HH         H       H       H H       H               H       HH       H

       n-Pentane, C5H12               iso-Pentane, C5H12            neo-Pentane, C5H12



Straight chain (直鏈)                           Branched chains (支鏈)
                                                                                         9
      Structural Isomers of Hydrocarbons
                     Boiling Point.

                                      The number of possible structural
                        36°C          isomers (異構體) of a chemical
n-Pentane, C5H12                      formula increases rapidly as the
                                      number of carbon atoms increases.



                        30°C
iso-Pentane, C5H12                     C5H12          3 isomers
                                       C8H18          75 isomers
                                       C20H42         366,316 isomers
                        10°C
neo-Pentane, C5H12


                                                                        10
Conformers – Same Molecule with
Different Spatial Orientations




                                  11
   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)
                                                              12
  Alkane –
  The Simplest Form of Hydrocarbon
                            H
Methane (CH4)
Natural Gas                 C
Biogas (marsh gas)     H        H
                            H



       H2
                           Butane (丁烷) (C4H10)
       C         CH3       Liquefied petroleum gas (液化石油氣)(LPG)
H3C         C
            H2             Lighter gas




                                                             13
Alkane –
The Simplest Form of Hydrocarbon
        H2        H2        H2         Octane Number
        C         C         C             (辛烷值)
  H3C        C         C         CH3
             H2        H2
                                             0

          Heptane


           CH3 CH3
    H3C
           C        CH
    H3C        C            CH3
               H2                           100


 2,2,4-Trimethylpentane
                                                       14
      Boosting Up the Octane Number

   Anti-Knocking Agent   Tetramethyl lead (四甲基鉛), Pb(CH3)4
         (抗震劑)           Tetraethyl lead (四乙基鉛), Pb(C2H5)4




        Benzene                     Toluene            p-Xylene
         C6 H 6                      C7 H 8             C 8H 10
    Octane No. = 106            Octane No. = 118   Octane No. = 116



                                   Cause air pollution -
Toxic – leukemia (白血病)
                                   Produce smog (煙霧)


                                                                      15
  Saturated and Unsaturated
  Hydrocarbons
Saturated Hydrocarbons – contain single bonds only
Unsaturated Hydrocarbons – contain multiple bonds


Saturated hydrocarbon             Unsaturated hydrocarbon
(飽和碳氫化合物)                         (不飽和碳氫化合物)

         H       H H       H       H       H   H       H

H            C         C               C           C
     C           C         H       H       C   C       H
 H       H H         H                 H           H

  n-Butane, C4H10                    But-2-ene, C4H8
     (丁烷)                              (丁-2-烯)
                                                            16
  Alkenes –
  Hydrocarbons with C=C Double Bonds
Ethene/Ethylene (乙烯) (C2H4) – The simplest alkene (烯)

  H         H   Use:      Making polymer (polythene)
      C C                 A plant hormone (triggers fruit ripening)
  H         H




                       beta-carotene
                       (胡蘿蔔素)

Beta-carotene is the precursor molecule to vitamin A


                                                                      17
Alkenes –
Hydrocarbons with C=C Double Bonds
  H               H           H               H           H               H

      C       C                   C       C                   C       C

  H               H           H               H           H               H

          H   H                       H       H               H       H
          C   C                       C       C               C       C
          H   H                       H       H               H       H

                                              Polymerization
                                                (聚合作用)

                  H   H   H   H       H       H   H   H   H       H
                  C   C   C   C       C       C   C   C   C       C
                  H   H   H   H       H       H   H   H   H       H           18
   Sigma (s) Bond and Pi (p) Bond
Compounds with double covalent bond

Ethene (CH2=CH2)                      Pi (p) – side-to-side overlap
Double covalent bond = 1 s bond + 1 p bond




            121.7°
        H                H
1.08Å                        116.6°
            C        C

       H 1.33Å H
  A double bond consists of                                           19
 one σ bond and one p bond
Geometrical Isomers (幾何異構體)
of Alkene
  H3C     CH3    H3C     H

    H     H        H     CH3

  cis-2-butene   trans-2-butene
   (順-丁-2-烯)       (反-丁-2-烯)




                                  20
   C=C Double Bonds:
   Absorption of Light
Compound                           max (nm)    (M-1cm-1)
H2C        CH2                       165         15,000

                                     217         21,000

                                     256         50,000

                                     290         85,000

                                     334        125,000

                                     364        138,000


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 = 10-9 m     21
         Sunscreens (防曬霜)

not very soluble
in oily skin lotions           O

                                   OH                          O     CH 2CH3
                                            (CH 3 )2N          COCH2 CHCH2 CH2 CH 2CH 3
              H2 N
            para-aminobenzoic acid              2-ethylhexyl 4-(dimethylamino)benzoate
                   PABA                                       Padimate O

                     absorb UV-B                             absorb UV-B

                                           O
                                                    CH2 CH3
                                               OCH2 CHCH2 CH 2CH 2CH3

                       CH 3O
                        2-ethylhexyl (E)-2-(4-methoxyphenyl)-2-propenoate
                                             Giv Tan F
                                        absorb UV-A & UV-B
                                                                                          22
C=C Double Bonds:
Absorption of Light


          -carotene (胡蘿蔔素)
               max = 455nm
      carrots, apricots, sweet potatoes
                  (orange)




              lycopene (番茄紅素)
                 max = 474nm
     tomatoes, watermelon, pink grapefruit
                      (red)                  1 nm = 10-9 m
                                                             23
  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.




some common aromatic compounds (芳香族化合物):

                                                    Cl

                                       Cl
    Toluene              Naphthalene    1,4-Dichlorobenzene
                                                              24
The Delocalization of Electrons in
Benzene
                H                           H
                 1                           1
H       6       C         H   H     6       C         H
        C            C2            C             C2
    5                             5
        C            C             C             C
H           4   C    3    H   H         4   C    3    H
                H                           H
                I                           II

                                  Resonance structures (共振結構) of benzene

                                                 H                          H
                                  H              C           H      H       C       H
                                  154 nm
                                            C             C133 nm       C       C 140 nm
                                            C             C             C       C
                                  H              C           H      H       C       H
                                                 H                          H              25
   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) .


                                  “cyclohexatriene” + 3H2
                                                                                  36 kcal/mol
                                                                                  (151kJ/mol)
               Potential energy




                                                               benzene + 3H2

                                        H° = -85.8 kcal/mol
                                           (-359kJ/mol)               H° = -49.8 kcal/mol
                                                                         (-208kJ/mol)


                                           cyclohexane

                                                                                             26
     Delocalization (離域作用)
     – Two More Examples
                  Delocalization in the carbonate ion
                                                                    2/3 -
   O-                     O                    O-          2/3 - O
O C                   O- C                 O- C               O C
                                                                   2/3 -
   O-                     O-                   O                 O

               Resonance Structures                       Resonance Hybrid


            Bonding in ethanoic acid and the ethanoate ion

 124 pm                                                    127 pm
                                                                       1/2 -
            O                  O                   O-                 O
       H3C C              H3C C               H3C C           H3C C
            OH                 O-                  O               O1/2 -
 143 pm                                                   127 pm

 Only one structure            Two equivalent resonance      Resonance Hybrid
 for the acid                  structures for the anion                        27
Organic Molecules are Classified
by Functional Groups

  H H                  Boiling point = - 88°C
           Ethane
H C C H
           (C2H6)      A gas at room temperature
  H H
                       Insoluble in water.


  H H H                Boiling point = + 78°C
H C C O    Ethanol     A liquid at room temperature
  H H     (C2H5OH)     Soluble in water
                       For making alcoholic beverages

  H H H
          Ethylamine   A corrosive (腐蝕性), pungent (刺激性),
H C C N
  H H H   (C2H5NH2)    highly toxic gas


                                                        28
  Organic Molecules
  are Classified    General
                   Structure
                                                   Name               Class

  by Functional   C OH                          Hydroxyl group      Alcohols
  Groups                           C C          Phenolic group       Phenols
                               C         C OH
                                   C C

                               C O C             Ether group         Ethers

Function group (官能基) is        C N
                                                 Amine group         Amines
defined as a combination of        O
                                                Ketone group         Ketones
atoms that behave as a unit.       C
                               C        C

                               O                  Aldehyde         Aldehydes
                               C
                                    H               group
                               O
                                                 Amide group         Amides
                               C
                                   N

                               O
                               C
                                                Carboxyl group   Carboxylic acids
                                   OH
                               O
                               C                 Ester group         Esters
                                   O C
                                                                               29
  Alcohols Contain the Hydroxyl Group
Alcohols are organic molecules in which a hydroxyl group is
bonded to a saturated carbon.

          H                                  OH
              H
        H
           C O                          H 3C C CH 3
          H                                  H
       Methanol                              Isopropanol
        (甲醇)                                   (異丙醇)
• Making methylated spirit               • Rubbing alcohol
• Fuel for racing car



                                                              30
  Alcohols Contain the Hydroxyl Group

                         H H
                       H C C OH
                         H H
                        Ethanol




Fermentation (發酵作用)

             enzymes              enzymes
(C6H10O5)x             C6H12O6              2 CH3CH2OH + 2 CO 2
  Starch                Glucose                Ethanol

                                                              31
  Transformation of Function Groups

Conversion of alkenes to alcohols (hydration水合作用)

                                  H+
     CH3CH CH2     +   H2O                    CH3CH CH2
                                  heat           OH H
       propene                                 2-propanol

                 An acid-catalyzed reaction



                                   without H +
       CH3CH CH2       +   H 2O                  No reaction


         propene
                                                               32
Interconversion of Alcohols and
Alkyl Halides

                 heat
 CH3OH +   HBr           CH3Br +       H2O
                        bromomethane




 CH3Br +   OH-          CH3OH +    Br-




                                             33
        Some Common Halogenated
        Hydrocarbons
           Some Halogenated Hydrocarbons
Formula         Common name            IUPAC name                Some important uses
                                       Derived from methane
CH3Cl           Methyl chloride        Chloromethane             Refrigerant; manufacture of
                                                                 silicones, methyl cellulose,
                                                                 and synthetic rubber

CH2Cl2          Methylene chloride     Dichloromethane           Laboratory and industrial
                                                                 solvent
CHCl3           Chloroform             Trichloromethane          Industrial solvent
CCl4            Carbon tetrachloride   Tetrachloromethane        (see text)

CBrF3           Halon-1301             Bromotrifluoromethane     Fire extinguisher systems
CCl2F2          CFC-12                 Dichlorodifluoromethane   Refrigerant

                                       Derived form ethane
CH3CH2Cl        Ethyl chloride         Chloroethane              Local anesthetic
ClCH2CH2Cl      Ethylene dichloride    1,2-dichloroethane        Solvent for rubber
CCl3CH3         Methylchloroform       1,1,1-trichloroethane     Solvent for cleaning
                                                                 computer chips and molds
                                                                 for shaping plastics           34
   Reactions of Alcohols and
   Halogenated Hydrocarbons
CH3CH2OH      +    CH3CH2Cl                 CH3CH2OCH2CH3
                                                 Diethyl ether
Diethyl ether was used as an anesthetic (麻醉劑) starting from
mid-19th century.
A commonly used laboratory solvent.

                                   •   It burns very completely and
MTBE as fuel additive (燃料添加劑)          reduces the emission of carbon
                                       monoxide.
                                   •   Very high octane rating (116),
                                       replace aromatic hydrocarbons
              O                    •   Very strong odor, sickening to
                                       some people.
Methyl tert-butyl ether (MTBE)     •   Decompose very slowly in nature,
                                       polluting the environment.
                                                                        35
        Different Types of Isomers

                                      Isomers



             Structural Isomers                      Stereoisomers
                (結構異構體)                              (立體異構體)
             (Different bonding)                   (Different shapes)


Positional    Hydrocarbon    Functional Group   Geometric     Enantiomers
 Isomers     Chain Isomers       Isomers         Isomers    (Optical Isomers)
位置異構體         碳氫鏈異構體           官能基異構體           幾何異構體          對映異構體
                                                              (旋光異構體)




                                                                            36
      Different Types of Isomers


                             Br
  Positional                                  Br     C5H11Br
   Isomers         Br




 Hydrocarbon
                        OH        OH               C4H9OH
Chain Isomers                            OH




Functional Group
                        OH        O    C4H10O
    Isomers


                                                               37
    Different Types of Isomers


                                   H3C
Geometric           H3C     CH3                C4H8
 Isomers                                 CH3




  Enantiomers
(Optical Isomers)
                          (See next page……)




                                                      38
  Optical Isomers and
  Chiral Compounds

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

                                                 *
                                              CH3CHCH2CH3

                                                   Br

                                              2-bromobutane

                                         Br                        Br

                                         C                         C    CH2CH3
                                H3CH2C        H              H
                                             CH3             H3C
                                                    mirror

                                     the two isomers of 2-bromobutane
                                                   enantiomers (對映異構體)

                                                                                 39
Conversion of Alcohols to
Aldehydes (醛)
                                   O          Very toxic
            liver enzymes
 CH3OH                             C
                                H     H
 Methanol                    Formaldehyde
                             LD50 = 0.070 g        The aldehyde
                                                      group
                                     O
             liver enzymes
CH3CH2OH                             C
                               CH3       H
  Ethanol                     Acetaldehyde     Less toxic
                              LD50 = 1.9 g

 Oxidation Reaction (氧化反應)



                                                                  40
  Some Common Aldehydes

• Large amounts of formaldehyde are       O
  used for producing adhesives for
  making plywood (夾板).                    C
                                      H       H
• Embalming (防腐)
                                      Formaldehyde
                                         (甲醛)




                                                     41
 Some Common Aldehydes
  Aldehydes      Structure             Food that contain the
                                            aldehydes
    Vanillin                  O          Vanilla Ice-cream
   (香草醛)                      C
                                   H

                 HO
                        O
                            CH 3

 Benzaldehyde                                Almond
    (苯醛)                     O
                             C
                                   H


Cinnamaldehyde           O                  Cinnamon
    (肉桂醛)             H    C H
                       C C
                           H

                                                             42
   From Wine to Vinegar
                           oxidation
           CH3CH2OH                         CH3COOH
             Ethanol                        Acetic acid
            an alcohol                    a carboxylic acid



White vinegar – 5% acetic acid solution          O

                                                       OH
                                                          Carboxyl group


                                                                      43
   Carboxylic Acids Found in Foods

AHAs
Alpha-hydroxy acids

AHAs contain a hydroxyl            O   OH    OH   O                   O   OH        O


group (-OH) bonded to the
                             HO    C   CH    CH   C   OH        HO    C   CH    CH2 C   OH


first carbon atom attached        Tartaric acid                      Malic acid
to the –COOH group.




                                                                O         OH        O

                                  HO   C   CH CH 3         HO   C    CH 2 C    CH 2 C   OH
                                       O   OH                         O   C
                                                                          OH                 44
                                   Lactic acid                        Citric acid
      Reactions of Carboxylic Acids
      with Alcohols
               O                                                            O
               C                                   H+
                          +    CH3CH2OH                                     C             + H2O
CH3CH2CH2            OH                                    CH3CH2CH2            OCH2CH3
      butyric acid                   ethanol                           ethyl butyrate
                                                                    (pineapple favour)


      O                                                         O
                                               +
      C                                        H
               + CH3CH2CH2CH2CH2OH                              C                          + H2O
CH3       OH                                              CH3       OCH2CH2CH2CH2CH3
acetic acid               pentanol                                   pentyl acetate
                                                                    (banana favour)



                                     O
                                     C                  ester linkage (酯鍵合)
                                           O
                                                                                             45
Some Esters (酯) and Their Odors
       Name                         Structure             Odor
Ethyl formate         HCOO—CH2CH3                      Rum
Isobutyl formate      HCOO—CH2CH(CH3)2                 raspberry
Ethyl acetate         CH3COO—CH2CH3                    Floral
Propy acetate         CH3COO—CH2CH2CH3                 Pear
Pentyl acetate        CH3COO—CH2CH2CH2CH2CH3           Banana
Isopentyl acetate     CH3COO—CH2CH2CH(CH3)2            Banana
Octyl acetate         CH3COO—                          Orange
                      CH2CH2CH2CH2CH2CH2CH2CH3
Benzyl acetate        CH3COO—CH2C6H5                   Jasmine
Isobutyl propionate   CH3CH2COO—CH2CH(CH3)2            Apple
Methyl butyrate       CH3CH2CH2COO—CH3                 Rum
Ethyl butyrate        CH3CH2CH2COO—CH2CH3              Pineapple
Butyl butyrate        CH3CH2CH2COO—CH2CH2CH2CH3        Pineapple
Amyl butyrate         CH3CH2CH2COO—CH2CH2CH2CH2CH3     Apricot
Isoamyl pentanoate    CH3CH2CH2CH2COO—CH2CH2CH(CH3)2   Apple

                                                                   46
      More About Oxidation and
      Reduction Reactions

    H   H                           O                         O
                - "2 H"                        + "O"
  H C O                             C                         C       H
               oxidation        H       H     oxidation   H       O
    H
  Methanol                   Formaldehyde                 Formic acid



  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
                                                                          47
   More About Oxidation and
   Reduction Reactions

                   O          + "2 H"         H   H
                   C                        H C O
               H       H    reduction         H
          Formaldehyde                      Methanol


               O                              H   H
               C       H   + "2 H", - "O"   H C O
           H       O
                            reduction         H
           Formic acid                      Methanol


Reduction (in organic chemistry) – often refers to:
• losing oxygen atoms (- O)
• gaining hydrogen atoms (+ H)

                                                       48
     More About Oxidation and
     Reduction Reactions
  H H H   H                     H H O                           H H O
                oxidation                         oxidation
H C C C O                     H C C C                         H C C C
  H H H                         H H H                           H H O H
 1o alcohol                       aldehyde                    carboxylic acid

     H
                                  O
  H O H
               oxidation    H     C     H
H C C C H                     C       C
                            H           H
  H H H                       H       H
 2o alcohol                    ketone


     CH3 H
 H3C C O                    Not easily oxidized
     CH3
               No H attached to the "C" atom
  3o alcohol                                                                49
          Amines (胺) and Amides (酰胺)

     Amines – substances with “fishy” smell.
                                            H3 C                      H3 C
     CH3 NH 2         CH 3CH 2 NH 2             N H                       N CH 3
                                            H3 C                      H3 C

          primary (1o ) amine         secondary (2o ) amine       tertiary (3 o) amine


     Amides – linking the amino acids in proteins

                                                    OH        HO
                      O                               O                      O             NH   N
          H               H                 H                 H                    H                N
S         N               N                 N                 N                    N
                  N               N                 N                    N
                  H               H                 H                    H
              O               O                 O   O             O                    O
    H2N   O
                                                        OH

                                                                         NH2
                                                                                                    50
 Organic Chemistry in Daily Life


• Polymers & Plastics (聚合物及塑膠)

• Detergents (清潔劑)




                                   51
       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.




      cotton                clothes made from silk        tire made of rubber
                                                                                52
                Natural polymers
  Cotton – mainly composed of cellulose (纖維素).
      OH                                               OH
                                   OH                                       H OH
               O         HO                                 O                         H
HO                                           O                                            O
                     O                           HO              OH    HO
 HO                                O                                                               OH
                                                                        HO
               OH                                           OH                    H
                              OH                 n-2                                      OH
                                                                              H                H
                             cellulose                                      -D-glucose

  Silk – natural protein fiber
                         O                             O                          O

       H3C         CH C       OH         H       CH C OH              H2C   CH C          OH

                   NH 2                          NH2                   OH NH 2
                   alanine                       glycine                    serine

  Rubber – formed from the polymerization of isoprene (異戊二烯)
                                                   ......                                               ......
           n

               isoprene                                               polyisoprene                               53
       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

                    H         H                             H H
Polythene (PE) n        C C           addition
                                                            C C
                                     polymerization
 (聚乙烯)              H         H                             H H   n



                                  H   H                       H H
                      n            C C      addition          C C
Polystyrene (PS)                      H    polymerization       H     n
   (聚苯乙烯)


Monomer (單體) –       low molecular weight compound that can be connected together to give
                     a polymer
                                                                                     54
         Condensation Polymerization
         (縮合聚合作用)
 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
                         O
                n                         OH   + n H2N
 Nylon              HO                                                      NH2
                                      O

                                  O
                                                   H
                                                   N                        + 2n H2O
                                                                      N
                                                                      H n
                                               O




Polyethylene                 HO            OH
terephthalate            n                         +       n HO       OH

(PET)                         O            O

(聚對苯二甲酸乙二酯)
                                                       O
                                                              O
“ A polyester – 聚酯”
                                                                       + 2n H2O
                                      O                O          n
                                                                                           55
   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.
polymer strands




         original form                        have little tendency to
                                              return to its original form
                            The chain can be stretched, which cause them to
                            flow pass each other, When released, the polymer
                            will not return to its original form.            56
   Thermosetting Plastics (熱固性塑膠)
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.




                                                                               57
  Soaps and Detergents
  (肥皂及清潔劑)

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.


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.

                                                                  58
   The Soap Molecule
                                                                         Na+
                                                                         or
                                                                         K+


Hydrophobic (疏水性) tail is attracted to oily,   Hydrophilic (親水性) head is
greasy, hydrocarbon-like substances.           attracted to water molecules.




CH3 (CH2)n CO2- Na+            n: even number, ranging from 8 - 16
    a soap molecule




                                                                               59
Breaking the Surface Tension




                               60
  Removing the Greasy Dirt




The soap molecules embed       The particles (micelles)
the hydrophobic tails into     repel each other, forming
the greasy dirt and leave it   many tiny suspended
off the surface.               droplets.
                                                           61
         Making of Soap :
         Saponification of Triglyceride
    Triglycerides are the principal constituents of animal fats and vegetable
    oils.
                 O                                                     O
      CH2    O   C   R                            CH2   OH         R   C   O- Na+
                 O                                                     O
                                           H2O
      CH     O   C   R'    +    3NaOH             CH    OH    +   R'   C   O-Na+
                                           Heat
                 O                                                     O
      CH2    O   C   R"                           CH2   OH        R"   C   O-Na+

        A triglyceride                             Glycerol            Soaps

   The saponification of a triglyceride.

            R, R’ and R”: Straight (unbranched) hydrocarbon chains.

saponification – 皂化作用; triglyceride – 甘油三酸酯                                         62
        Soap and Hard Water (硬水)

    Hard water:
    •     high mineral content
    •     rich in calcium ions (Ca2+) and magnesium ions (Mg2+)
    Soap forms insoluble precipitates (soap curd) with hard water. It
    reduces the cleaning power of soap.


     2 CH3 (CH 2) nCO2 - Na +   + Ca2+           (CH 3(CH 2) nCO2 -) 2 Ca 2+
         aqueous solut ion                        insoluble pr ecipitat es

     2 CH 3 (CH2 )n CO 2- Na+   + Mg2+           (CH3 (CH2 )n CO2- )2 Mg 2+
         aqueous solution                         insoluble precipitates


precipitate – 沉澱物                                                              63
   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.
                                   O O
                                    S - +
                                  O O Na


Sodium lauryl sulfate (SLS) or sodium dodecyl sulfate (SDS)




       R             SO3- Na+      R = alkyl group


             Sodium alkylbenzenesulfonate
                                                                      64

								
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