Learning Center
Plans & pricing Sign in
Sign Out

Organic - Download Now DOC

VIEWS: 122 PAGES: 17

									                     Chapter 9. Organic Chemistry

    Organic chemistry is the chemistry of compounds containing carbon. You
may encounter many organic compounds everyday. Some of them are ethanol
(grain alcohol), ethylene glycol (automobile antifreeze), and acetone (nail polish
    At one time, organic compounds were thought to be synthesized by living
organisms. In 1828, Friedrich Wöhler set out to synthesize ammonium cyanate,
NH4OCN, as in the following reaction.

                      AgOCN + NH4Cl  AgCl + NH4OCN

  The white crystalline product he obtained from the solution had none of the
properties of ammonium cyanate, even though it had the same composition.
This compound was not NH4OCN but (NH2)2CO (urea), an organic compound.
  A unique feature of carbon is its ability to bond to other carbon atoms to
give chains and rings of various lengths. Almost all elements have limited
ability to form such chains or rings of like atoms, but only carbon does this with
more than a few atoms. Other atoms, such as nitrogen, oxygen, and sulfur, may
be bonded to the carbon atom by single or multiple bonds.

I. Hydrocarbons (HC)
   The simplest organic compounds are hydrocarbons, compounds containing
only carbon and hydrogen. Hydrocarbons are classified into two main types,
aromatic or aliphatic, depending on whether they contain benzene rings or not.

  Hydrocarbons (HC):

 ① Aliphatic HC        Saturated HC: Alkane (CnH2n+2), Cycloalkane (CnH2n)
                       Unsaturated HC: Alkene (CnH2n), Alkyne (CnH2n–2)

 ② Aromatic HC: Benzene and its derivatives, fused rings

                                   Chapter 9-1
1. Saturated hydrocarbons
    They have only single covalent bonds. In these compounds, the bonds (or
carbons) are said to be “saturated”.

1) Alkane [CnH2n+2, sp3 carbons, methane (CH4) family (or paraffin)]

 a) The melting points and boiling points generally increase from methane to
  decane in the series. This is a result of increasing intermolecular forces,
  which tend to increase with increasing molecular weight.

    Table. Physical properties of straight-chain alkanes
    Formula                    Name         mp (ºC)     bp (ºC)
    CH4                        Methane        –183        –162
    C2H6      CH3CH3           Ethane         –172         –87
    C3H8      CH3CH2CH3        Propane        –187         –42
    C4H10     CH3(CH2)2CH3     Butane          138         –0.5
    C5H12     CH3(CH2)3CH3     Pentane        –130          36
    C6H14     CH3(CH2)4CH3     Hexane          –95          69
    C7H16     CH3(CH2)5CH3     Heptane         –91          98
    C8H18     CH3(CH2)6CH3     Octane          –57         126
    C9H20     CH3(CH2)7CH3     Nonane          –54         151
    C10H22    CH3(CH2)8CH3     Decane          –30         174

 b) The boiling points are related to molecular masses and shapes.

   Family      Isomer             bp (ºC)      Family        Isomer                bp (ºC)
   Butane      butane                 0.5      Hexane        hexane                  68.7
               isobutane             11.7                    3-methylpentane         63.3
   Pentane     pentane               36.1                    isohexane               60.3
               isopentane            27.9                    2,3-dimethylbutane      58.0
               2,2-dimethylpropane    9.5                    2,2,-dimethylbutane     49.7

                                         Chapter 9-2
2) Cycloalkane [CnH2n, sp3 carbons, ring compounds]
 a) Some cycloalkanes

           Compound                         Angle, C-C-C                   Stability

          Cyclopropane                            60o                      unstable

          Cyclobutane                             90o                      unstable

          Cyclopentane                           108o                           stable

          Cyclohexane                            120o                      unstable

b) In cyclohexane, hydrogen atoms on the first and fourth carbon atoms in
 the boat form come close together enough to repel each other. In the chair
 form, the H atoms do not interfere with each other. The chair form is the
 more stable conformation of cyclohexane.

                H                 H                             H              H

                C H           H   C                     H       C H                C       H
                          C                                                                H
            H                           H                              C           CH
                H             C              H                   C         C
                      C   H             C                             H                H
                                                                H           H
                      H                 H
                          chair form                                boat form

2. Unsaturated hydrocarbons
    They are compounds that contain some multiple (double or triple) bonds
between carbons and said to be “unsaturated”.

1) Alkene [CnH2n, sp2 carbons, ethylene (C2H4) family]
 a) If there is one double bond in the molecules, the hydrocarbons are the
 simple alkenes or olefins.

                                       Chapter 9-3
        CH2=CH2 (etylene or ethene), CH3CH=CH2 (propylene, propene)

 b) Bonding (hybrid theory)

                                             C C

                                    1 + 1 bonds

2) Alkyne [CnH2n–2, sp carbons, acetylene (C2H2) family]
 a) Some alkynes have one triple bond in their molecules.
    Example: C2H2 (acetylene or ethyne)

 b) Bonding (hybrid theory)

                                        C C
                                    1 + 2 bonds

3. Aromatic hydrocarbons
    Aromatic hydrocarbons contain benzene rings or six-membered rings of
carbon atoms with alternating single and double carbon–carbon bonds.

1) The electronic structure of these rings may be represented by resonance
formulas. For example, benzene is given the condensed formula, where the
circle represents the delocalization of -electrons.

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

                                     Chapter 9-4
2) Bonding

3) Aromatic compounds: vitamins, proteins, hormones

                               benzopyrene: carcinogen

4) Some examples

                     CH3                 CH2CH3

               methylbenzene         ethylbenzene          biphenyl
               = toluene
                               CH3                           CH3

                      CH3            CH3
                                                      or xylene
                       or mesitylene

4. Reactions of hydrocarbons

1) Oxidation. All hydrocarbons burn in an excess of O2 to give CO2 and H2O.
The large negative H values explain why the hydrocarbons are useful as fuels.

   C2H6(g) + 7/2O2(g)  2CO2(g) + 3H2O(l)                  H = –1560 kJ/mol
   C6H6(l) + 15/2O2(g)  6CO2(g) + 3H2O(l)                 H = –3267 kJ/mol

                                     Chapter 9-5
2) Reactions of alkanes: substitution
   Saturated hydrocarbons have low reactivity toward most chemical reagents.
Because of this, they have become known as paraffin hydrocarbons (Latin,
parum, little; affinis, reactivity).

       CH4 + Cl2  CH3Cl + HCl (heat or light)
       CH3Cl + Cl2  CH2Cl2 + HCl
       CH2Cl2 + Cl2  CHCl3 + HCl
       CHCl3 + Cl2  CCl4 + HCl

 Mechanism (radical reaction)

 ① Initiation:       Cl:Cl  2Cl·

 ② Propagation       H3C:H + Cl·  H3C· + H:Cl
                     H3C· + Cl:Cl  H3C:Cl + Cl·

 ③ Termination       Cl· + Cl·  Cl:Cl (or Cl2)
                     H3C· + Cl·  H3C:Cl
                     H3C· + CH3·  H3C:CH33

                                 Chapter 9-6
II. Isomers
    These are compounds that have the same molecular formula but different
structural formulas.

1. Structural isomers

1) Skeletal isomers. They differ in the carbon chains (linear versus branched

  Isomers of pentane (C5H12)

                                         C        C
                        C C C C C    C C C C    C C C

2) Positional isomers. They differ in the position on a hydrocarbon chain or
ring where a functional group (or groups) is attached.

 a) Isomers of butene

                        C C C C      C C C C    C C C

 b) Isomers of bromopentane (C5H11Br)

                                     Br        Br         C
           C C C C C Br        C C C C C   C C C C C    C C C Br

               C               C          C     Br  C
           C C C C Br      C C C C   C C C C    C C C C
                               Br      Br

2. Stereoisomers
    In stereoisomers, the number and types of atoms and bonds are the same,
but certain atoms are oriented differently in space.

                                  Chapter 9-7
1) Geometric isomers. Rotation about a C=C double bond is severely

                                   Y        X       Y          Y

                                   X        Y       X          X
                                       trans             cis

2) Enantiomers
   Structures that are nonsuperimposable mirror images of each other are
called enantiomers and said to be chiral. Because of their ability to rotate the
plane of the polarized light, isomers of these types are said to be optically
active and they are called optical isomers.

 a) Optical activity: Ability to rotate the plane of the polarized light.
  i)    d-form: clockwise rotation (dextrotary)
  ii)   l-form: counterclockwise rotation (levorotary)

 b) Diastereomers: stereoisomers that are not mirror images (enantiomers)
 c) Chiral carbon (or asymmetric carbon): CWXYZ

                         H                                              H

                         C                                              C
                                       Cl                 Cl
              I                                                               I
                                 Br                                Br

  Figure. The two optical isomers of CHClBrI are mirror images (enantiomers) of each other.

 d) A racemic mixture: a mixture of enantiomers. It produces no net rotation of
  the plane of the polarized light.
 e) Resolution: Separation of the d and l isomers of a racemic mixture is
  called resolution.

                                         Chapter 9-8
III. Nomenclature: IUPAC (International Union of Pure and Applied

1. Rule

① Select the longest, continuous carbon chain containing the functional group.
② Number the carbon atoms of the continuous base chain so that the
substituents and functional groups appear at the lowest possible numbers.
③ Give each substituent a name and number.
  a) For identical groups: di (two), tri (three), tetra (four), penta (five)
  b) For different groups: in alphabetical order

2. Some remarks

1) Alkane: CnH2n+2 = RH,               R: alkyl (CnH2n+1)

 CH3: methyl,       C2H5 (or CH3CH2): ethyl,   CH3CH2CH2: propyl
 CH3CHCH3: isopropyl       CH3CH2CH2CH2: butyl
 CH3CH(CH3)CH3: isobutyl

2) Whenever alternative base chains of equal length are possible, always
name a compound so as to have the maximum number of side chains

 a) Exercise: Assign IUPAC names to the following compounds.

                  CH3                                 CH3 H2C           CH3
                 CH        C                         CH      CH      CH
           H3C        C         CH3            H3C         C       C       CH3
                      H2                                   H2      H2

     H3C             CH3                                                  CH3
                                      H2              H2                          H
           C     C              H3C   C    C     C    C    CH3           CH       C       CH2
                                                                   H3C        C       C
     H3C             CH3                                                      H       H

                                               Chapter 9-9
 b) Exercise: Write structures for the following compounds
  i)    2-methylbutane
  ii)   2-pentyne
  iii)  2-ethyl-1-butene
  iv)   1,5-octadiene
  v)    2-ethyl-3-methyl-1-pentene

IV. Functional groups
    Certain groups of atoms in many organic molecules are particularly reactive
and have characteristic chemical properties. A functional group is a reactive part
of a molecule that undergoes predictable reactions.

   Table. Some organic functional groups
   Functional           Name of             Example
   group                functional group
   R–X                  halide              CH3Cl (chloromethane)
   (X = F, Cl, Br, I)
   R–OH                 alcohol             C2H5OH (ethanol or ethyl alcohol))
   R–CHO                aldehyde            CH3CHO (ethanal or acetaldehyde)
   R–COR'               ketone              CH3COCH3 (acetone or propanone)
   R–NH2                amine               CH3CH2NH2 (ethyl amine)
   R–O–R'               ether               CH3CH2–O–CH2CH3 (diethyl ether)
   R–COOH               carboxylic acid     CH3COOH (acetic acid)
   R–COOR'              ester               CH3COOCH2CH3 (ethyl acetate or ethyl ethanolate)
   R–CONH2              amide               CH3CONH2 (acetamide or ethanamide)
   R–COX                acid halide         CH3COCl (acetyl chloride or ethanoic acid)
   R–CO–: acyl group
   RR'C=CRR'            alkene              CH2=CH2 (ethylene or ethene)
   R–CC–R'             alkyne              HCCH (acetylene or ethyne)
   R and R' are general hydrocarbon groups

                                           Chapter 9-10
1. Alkenes

1) Preparation: elimination
    The general laboratory preparation of alkenes uses an elimination reaction,
in which two atoms are eliminated from the adjacent carbon atoms.

                           H H
                                                    H2SO 4
                       H3C C C H                              CH 3CH=CH              2   + H 2O
                          HO H
                           H H
                       H3C C C H           CH 3CH=CH                                 2   + H 2O + KBr
                           H Br

            H3C                H                       H3C                   H                    O
                                   H                                             H
       a)         C        C                                     C       C               +   O    S   OH
            H                                           H
                               H                                             H                    O
             HO                                              O
                       H O                             H         H
                        O S OH

                  H3C                  H                    H3C                  H
                                           H    - H2O                                    H   - H2SO4 H3C               H
                          C        C                                 C       C                                 C   C
                  H                                          H
                                       H                                         H                         H           H
                      O                                                                           O

                  H        H                                                                 O    S   OH
                      H3C                  H
                                                                 H3C                 H
                                               Br     - Br
       b)                      C       C                                 C       C
                      H                               - H2O
                                           H                         H               H


2) Reactions

 a) Electrophilic addition. The presence of carbon–carbon double or triple
  bonds in hydrocarbons markedly increases their chemical reactivity. The most
  characteristic reactions of alkenes and alkynes are addition reactions, in
  which a reactant is added to the atoms that form the multiple bond.

                                                       Chapter 9-11
b) Markovnikov's rule: When an unsymmetrical reagent (HX, HOR, HCN,
 HOSO3H) is added to an asymmetrical alkene or alkyne, the more positive
 fragment (usually H) is added to the carbon atom with the greater number of
 hydrogen atoms.

① CH2=CH2 + Br2  CH2BrCH2Br
② CH3CH=CHCH3 + H2  CH3CH2CH2CH3 (500 ºC, Ni catalyst)
③   CH3CH=CH2 + HBr  CH3CH(Br)CH3 (2-bromopropane)
④   CH3CH=CH2 + HOH  CH3CH(OH)CH3 (H+ catalyst)
⑤   CH3CCH + 2Cl2  CH3CCl2–CCl2H
⑥   CH3CH2CCH + 2HBr  CH3CH2CBr2–CH3

c) Polymerization
 i)    Monomer versus polymer
 ii)   Addition versus condensation

Table. Some polymers
Monomer                Polymer                   Uses
CH2=CH2                polyethylene              High density: molded containers, lids, toys,
                                                 Low density: packing, trash bags
CH2=CHCH              polypropylene             containers, lids, carpeting, rope
CH2=CHCl               poly(vinyl chloride)      Water pipes, roofing, credit cards, records,
                       PVC                       hoses
CF2=CF2                poly(tetrafluoroethylene) bearings, insulation, gaskets, industrial ware
CH2=CH(C6H5)           polystyrene               packing, refrigerator door, cups
HOCH2CH2OH and         poly(ethyleneglycol)      textile fabrics, fire hoses, ropes
1,4-C6H5(COOH)2        Dacron
H2N(CH2)6NH2 and       poly(hexamethylene        hosiery, rope, tire, cord, fish line, parachutes,
HOOC(CH2)6COOH         adipamide), Nylon 66      artificial blood vessel
HO(CH2)4OH and         polyurethane              spandex fibers, bristles for brushes, cushions,
OCN(CH2)6NCO                                     mattresses (as foam)

                                        Chapter 9-12
2. Aromatic hydrocarbon

1) Typical reaction: electrophilic substitution reaction
   Although aromatic hydrocarbons are formally unsaturated, they do not
readily undergo addition reactions. The delocalized  bonding causes aromatic
compounds to behave quite differently from alkenes and alkynes. For example,
benzene does not add Cl2 or Br2 to its double bonds under ordinary conditions.
In contrast, aromatic hydrocarbons undergo substitution reactions relatively

                Br 2
               FeBr 3                                  FeBr 3 + Br 2            FeBr4- + Br+
               HNO 3                                                                        H
                                  NO 2
            H2SO 4                                                                          Br
                                                                  + Br+                 +
          CH 3CH 2Cl                                                                        H
                                                                 H        Br   FeBr 3
                                  CH2CH3                                                         Br
            AlCl 3                                               Br
           (Friedel-Crafts alkylation)                           H
            H2SO 4                                                                      + FeBr 3 + HBr
                                   SO 3H

                    O            O                                O   H           O
          a)      O N O H   H O S OH                            O N O   +       O S OH
                                 O                                    H           O
                     O   H - H2O     O
                   O N O           O N                                 O N O
                                        Cl        - AlCl4
          b)     H3CH2C    Cl          Al                        H3C CH2
                                  Cl         Cl

                    O               O                          O   H                O
          c)     HO S OH        H O S OH                    HO S O   +            O S OH
                    O               O                          O   H                O

                          O   H - H2O                  O
                       HO S O                          S
                                                  HO        O
                          O   H

                                        Chapter 9-13
2) Ortho- and para-directing groups
   We use the terms "ortho", "meta", and "para" (o-, m-, p-) when there are two
substituents on the benzene ring. Ortho refers to substituents on adjacent
carbon atoms, meta to substituents with one carbon atom between them, and
para to substituents opposite to each other on the ring.

                       Br 2                 HNO 3
                                     Br                O2N     Br
                      FeBr 3                H2SO 4

                      HNO 3                     Br 2
                                     NO 2                    NO 2
                      H2SO 4                 FeBr 3

 a) Ortho-, para-directing groups: –NH2 > –OR > –OH > –R > –X
 b) Meta-directing groups: –NO2 > –CN > SO3H > –CHO > –COR > –COOH >

3. Alcohols
    Alcohols are hydrocarbon derivatives in which one or more hydrogens of a
parent hydrocarbon have been replaced by a hydroxyl or alcohol functional
group, OH.

1) Preparation
   Alcohols can be prepared by the hydration of alkenes or the hydrolysis of
alkyl halides.

 a) CH3CH=CH2 + H2O  CH3CH(OH)CH3 (in the presence of acid such as

 b) CH3CH2CH2Br + OH–  CH3CH2CH2OH + Br–

                                 Chapter 9-14
                                H        H O                                       H             O
         a) H3CHC           C             O S OH                  H3CHC        C           +   O S OH
                                H           O                                      H             O

                              H               H3C             H       - H2SO4 H3C                  H
                                    H                             H                                    H
              H3CHC         C                       C     C                                C   C
                                              H                                        H
                                 H                            H                        HO          H
                      H2O                     H       H
                                                              O S OH

               H3C                   H                    H3C              H
                                         Br   -Br                              H
         b)             C       C                                 C    C
                H                                         H
                    H                H                                     OH

2) Alcohols are classified according to the number of carbon groups bonded to
the carbon that contains the OH group.

                 H               R'                R'
               R C OH          R C OH            R C OH
                 H               H   (secondary)   R"  (tertiary)

                        [O]                         [O]                            [O]

                RCHO                          RCOR'                        No reaction

3) Polyhydroxyl alcohols. A polyhydroxyl alcohol has more than one OH group.

 a) CH2(OH)–CH2(OH), ethylene glycol (1,2-ethanediol): water-soluble, high bp,
  automobile antifreeze
 b) CH2(OH)CH(OH)–CH2(OH), glycerol (1,2,3-propanetriol): water-soluble,
  able to take up moisture from the air (lotions and cosmetics)

4) Esterification and saponification

 a) Esterification, Carboxylic acids react with alcohols to give esters, when
  these substances are heated together in the presence of an inorganic acid,

                                               Chapter 9-15
such as H2SO4. This is a type of a condensation reaction, in which two
molecules are joined by the elimination of a small molecule such as water.

                  R C        + H O R'      RCOOR' + H   2O

b) Saponification. Saponification is the hydrolysis of an ester in the
presence of a base. The term, which came from the Latin "soap" (sapon),
originated from the soap making. In this process, an animal fat or a vegetable
oil is boiled with a strong base, usually NaOH.

        H2C O OCC 17H35                 H2C OH
                                                            -   +
         HC O OCC 17H35 + 3 NaOH         HC OH + 3 C17H35COO Na
        H2C O OCC 17H35                 H2C OH       (soap)

                                Chapter 9-16
V. Raw materials for organic chemicals

1. Coal

1) Coal  coke + coal tar + coal gas (heating in the absence of air)

2) Coal gas: a mixture of H2, CH4, CO, C2H6, NH3, CO2, H2S, …

3) Coal tar fraction

   Bp range (ºC)       Name          Mass (%)       Primary constituents
   below 200         light oil           5          benzene, toluene, xylenes
   200–250          middle oil           17         naphthalene, phenol, pyridine
                   (carbolic oil)
   250–300          heavy oil            7          naphthalenes and methylnaphthalenes,
                                                    cresols, quinoline
   300–350           green oil           9          anthracene, carbazole
   residue               -               62         pitch or tar

2. Petroleum: fractional distillation

   Bp range (ºC)   Composition Fractions            Uses
   0–30                C1–C4            gas         gaseous fuel
   30–60               C5–C7 petroleum ether        solvents
   60–100              C6–C8           ligroin      solvents
   70–150              C8–C9         gasoline       motor fuel
   175–300           C10–C16         kerosene       jet fuel, diesel oil
   over 300          C16–C18          gas-oil       diesel fuel, cracking stock
                     C18–C20          wax-oil       lubricating oil, mineral oil, cracking stock
                     C21–C40        paraffin wax    cradles, wax paper
                    above C40        residuum       roofing tar, road materials, waterproofing

                                              Chapter 9-17

To top