Chapter 9. ORGANIC CEMISTRYMost kown chemical compounds are carbon-containing organic compounds with carbon atoms in straight chains, branched chains, or rings (Figure 9.1)

Structural formula ofdichloromethane intwo dimensions

Representation of the three-dimensional structure ofdichloromethane

Cl atoms toward viewer

H atoms away from viewer

C

H

H

Cl ClCl

H

H

CCl• Figure 9.2. The

molecular geometry of organic chemicals is an important characteristic

9.2. HYDROCARBONS (Figure 9.3)Alkanes are hydrocarbons in which the carbon atoms are joined by single bonds consisting of two shared electronsAlkenes have at least one double bond between C atomsAlkynes have at least one triple bond between C atomsAromatic (aryl) hydrocarbons have characteristic ring structures, usually consisting of 6 C atoms (benzene ring)

2-Methylbutane 1,3-Butadiene(alkane) (alkene)

Acetylene(alkyne)

Benzene Naphthalene(aryl compound) (aryl compound)

H

H

H

C

H

H

C

H

CH3

C

H

H

CH

HHC

CCHH

H CH HC CH

Figure 9.4. Structural formulas of four alkanes each containing 8 C atoms

1,4-Dimethylcyclohexane

n-Octane 2,5-Dimethylhexane

65

4

32

1

3-Ethyl-2-methylpentane

1 2 3 4 5 6HC

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

H

H

H

H

H

H

C

H

C

H

C

H

H

C

H

H

C

H

C

H

C

H

H

C H

H

H

H

H

H

C

H

C

CH H

C

H

H H

H

C

H

HH C

H

C

H

H

CH H HC

C C

C

CCH

H HH

HHHH

H

H

H

C C

H

H

H

Formulas of AlkanesA molecular formula, such as C8H18, may apply to a number of different alkanes containing 8 C atoms (Figure 9.4)• Isomers in straight chains, branched chains, and rings• Isomers are shown by structural formulasAlkanes and alkyl groups (examples below):

H C

H

H

H

H C C H

H

H

H

H

H C C C H

H

H

H

H

H

H

Methane

Ethane

n-Propane

H C

H

H Methyl group

H C C

H

H

H

H Ethyl group

H C C C

H

H

H

H

H

H n-Propyl group

Names of Alkanes and Organic NomenclatureSystematic names from which the structures of organic molecules can be deduced (see examples below)Common names without structural implications1. Based on longest continuous chain of C atoms2. Longest chain is numbered from one end3. Substituent groups by number of carbon attached and by name4. Prefixes to denote multiple substitutions

H C

H

H

C C C

H

C

H

H

H

H H

CH3H3C

CH3

Example: 2,2,3-Trimethylpentane

Reactions of AlkanesCombustion (example of burning propane fuel)• C3H8 + 5O2 3CO2 + 4H2O

Substitution reactions, such as those used to make organohalides• CH4 + Cl2 CH3Cl + HCl

Alkenes and AlkynesAlkenes have at least one double bond consisting of 4 electrons shared between carbon atomsSimplest alkene is ethylene (ethene)

• Ethene is a very important industrial chemical produced in large quantities for the manufacture of polyethylene plastic and other chemical products

1,3-Butadiene (Figure 9.3) is widely used to make synthetic rubberAlkynes have a triple bond (6 shared electrons) between C atoms• Acetylene, C2H2, Figure 9.3, is the simplest alkyne

• Acetylene is widely used in welding

C CH

H

H

HEthylene (ethene)

Addition Reactions of Alkenes and AlkynesAlkenes and alkynes are unsaturated hydrocarbons because they have additional electrons available for bonding in their double and triple bonds• Unsaturated bonds enable addition reactions

C CH

H

H

HC CHH H

H H

HH H+

+ CCl

HH

HCHCH C H Cl

Alkenes and Cis-trans IsomerismSince rotation cannot occur around a double bond, cis and trans isomers are possible as shown in figure 9.5

Cis-2-butene Trans-2-buteneH

H H

H

H

H

H

C

CC

C

H

HC

H

H

H

C

H C

C

H

H

H

Condensed Structural FormulasThe structural formula of 3-ethyl-4-methylhexane (below) can be represented by the condensed structural formula CH3CH2CH(C2H5)CH(CH3)CH2CH3

H C C C C C C

H H

H H

H H

H H

H

H

C

CH

H H

H H

HC

H

H H

Figure 9.6. Representation of Structural Formulas with Lines

C

C C

C

CCH

H HH

HH H

H

CC

H

H

H

H

H

HH H

Cl

(See structural formulas of these compounds in Figure 9.5)

1,4-Dimethylcyclohexane1-H atom

2 H atoms3 H atoms

Represented as

3-Ethyl-3-methylpentane

3 H atoms2 H atoms

0 H atoms

Represented as

A Cl atom substi-tuted for 1 H atom

Represented as

Trans-2-buteneCis-2-butene

2-Chlorobutane

H

H

H

H

H

C

H

H

C

C

H

C

C H

H

H

C

H

H

H

H

H

C C

H

H

HC

H

HCl

H

C

H

H

CH

H

H

C

Aromatic (Aryl) Hydrocarbons and Aromatic (Aryl) CompoundsFigure 9.7. Representation of benzene, an aromatic compound

Aromaticity• Aromatic compounds have ring structures• Particularly stable bonds that contain delocalized clouds of (“pie”)

electrons (resonance stabilization)• Low hydrogen/carbon ratio• Tend to undergo substitution reactions characteristic of alkanes

rather than addition reactions characteristic of alkenes

HH

HH

H

H

HH

H

HH

H

C atom bonded with 1 H atom

Figure 9.8. Some Aromatic Compounds

Polycyclic Aromatic HydrocarbonsCondensed ring systems typified by benzo(a)pyrene, Figure 9.8

• Carbon-rich hydrocarbons• Formed by preferential combustion of hydrogen in hydrocarbons

under oxygen-deficient conditions• Sources include engine exhausts, wood stove smoke, cigarette

smoke, and charbroiled food• Some, notably benzo(a)pyrene, are metabolized to carcinogens

Type of group Example Group formulaTable 9.2. Important Functional Groups Characterized by Specific Groupings of Atoms

Figure 9.9. Examples of Oxygen-Containing Organic Compounds

Figure 9.10. Example Organonitrogen Compounds

• Methylamine is a bad-smelling, toxic, basic compound• Dimethylnitrosamine is a carcinogen• 2,4,6-Trinitrotoluene is a high explosive• Organonitrogen compounds include herbicides, insecticides, many

other kinds of substances

Trisodium Nitrilotriacetate (NTA), an Organonitrogen Compound that is a Strong Metal Chelating Agent

Figure 9.11. Some Important Organohalide Compounds

Figure 9.12. Halogenated Naphthalenes and Biphenyls

• PCBs are important, persistent water pollutants

Cl

(Br)1-10

2-Chloronaphthalene

(Cl)1-10

(Cl)1-8

Polychlorinatednaphthalenes

Polychlorinated biphenyls (PCBs)

Polybrominatedbiphenyls (PBBs)

Chlorofluorocarbons, Halons, and Hydrogen-Containing ChlorofluorocarbonsChlorofluorocarbons (CFCs) are volatile low-molecular-mass compounds in which Cl and F are bonded to carbon• Were widely used as refrigerants, foam blowing, in aerosol sprays• Now phased out because of destruction of stratospheric ozoneHalons are organobromine compounds• Fire retardents• Harmful to stratospheric ozoneHydrohalocarbons are H-containing chlorofluorocarbons or fluorocarbons that substitute for CFCs• More reactive H-C bonds in hydrohalocarbons enable their

destruction at low altitudes so that they do not reach the stratosphere where they could affect stratospheric ozone

Chlorinated PhenolsPentachlorophenol has been a significant hazardous waste material and water pollutant until it was banned

Cl

Cl

Cl

Cl

Cl

OH

Pentachlorophenol

Figure 9.13. Some Organosulfur Compounds

SHH

H

CH

H

CHCH

H

H

H

CH

C

H

CH

H

C SH

H

HSHC

H

HH

SH

Thiols

Methanethiol 2-Propene-1-thiol 1-Butanethiol Benzenethiol

Sulfides and Cyclic Sulfides

Thiourea Compounds

Thiourea

Thiophene (an unsat-urated sulfide)

Thiophane

NR

R

S

CR

RNN

H

H

S

CH

HN

NH

HC

S

HN

HS

H

CH C

H

H H SS

Organic derivatives of thiourea (R is a hydrocarbon group

1-Naphthyl-thiourea (ANTU)

Dimethyl sulfide

O

O

HH

H

C C

H

HO S OH

H

H

O

O

SCH O OH

OHS

O

O

O

S

O

H

H

C

H

H

C

H

H

C

H

H

C

H

H

CH

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

O- Na

+

H C S C H

H

H

H

H

O

SOO

Figure 9.13 (Cont.)Sulfoxides and Sulfones

Sulfonic Acids and Salts

Dimethylsulfoxide (DMSO)

Sulfolane

Benzenesulfonic acid Sodium 4-decylbenzenesulfonate

Methyl sulfate Ethyl sulfate

Organosulfate Esters

Figure 9.14. Organophosphorus Compounds

9.4. SYNTHETIC POLYMERSThe synthetic polymers industry is huge with important implications for sustainability, materials, and the environmentPolymers are formed by the joining together of small molecules called monomers

• Many natural products are polymers, such as cellulose in wood or cotton, a polymer of glucose sugar

• Polymers are the basis of many industries, such as rubber, plastics, and textile manufacture

Figure 9.15. Formation of Polyvinylchloride Polymer

• Polyvinylchloride is used in a wide variety of applications including PVC pipe manufacture

Figure 9.16. Monomers in Widely Used Polymers

• Polyethylene (plastic bags, milk cartons)• Polypropylene (impact-resistant plastics, indoor-outdoor carpets)• Polyacrylonitrile (Orlon, carpets)• Polystyrene (foam insulation)• Polytetrafluoroethylene (Teflon coatings, bearings)

Figure 9.17. Polymeric Cation Exchanger

- Na+-Na+

......

...... C C C C C C

C C C C C C

H H

H

H

H

H

H H

H

H

H H H H

H

H

H

H

H

O3S SO3

SO3-Na+

Sustainability and Environmental Implications of Polymers• Monomers pose environmental and safety hazards• Volatile, combustible, explosive polymers, such as ethylene• Combustion of polymers can produce noxious products, such as

HCl from combustion of polyvinylchloridePlasticizers used in polymers may cause environmental problems• Phthalate plasticizers are environmentally persistent, resistant to

treatment processes and prone to undergo bioaccumulation

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