Chapter 20Organic

Chemistry

Roy KennedyMassachusetts Bay Community College

Wellesley Hills, MA

Chemistry: A Molecular Approach, 2nd Ed.Nivaldo Tro

Copyright 2011 Pearson Education, Inc.

What Is Organic Chemistry?• Organic chemistry study of carbon containing

compounds, their properties and their reactions Organics can also contain hydrogen, nitrogen, oxygen, sulfur. Organic compounds are found in all three states

solids tend to have low melting pointsgases tend to be low molar mass

• Life exists because of organic chemistry Biochemistry is a closely related field

• Organic molecules range from simple to very large and complex

It is this complexity that allows the complex functions of the cells to occur

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Organic Compound’s Properties

• Solubility in water varies depending on the number of carbonswhat other elements are attached to C and how many of those other elements there are, e.g. ,

CH3OH is miscible with water, but C10H21OH is insoluble

• Most common smells are caused by organic moleculesOdorants must be volatile (low molar mass), but not all

volatile substances have a scentOur sense of smell helps us identify food, people, and

other organisms, and alerts us to dangers such as polluted air or spoiled food

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Differences Between Organic and Inorganic Compounds

• Organic compounds are easily decomposed into simpler substances by heating, but inorganic substances are not

• Inorganic compounds are readily synthesized in the lab, but synthesis of organic compounds in the lab is more difficult

• carbon monoxide, carbon dioxide, carbonates, and carbides are not organic compounds

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Bond Energies and Reactivities

5

Carbon-carbon bonds are very strong and non-reactive

Carbon Bonding• There are millions of different organic

compounds because carbon can form single, double, or triple bonds

• Carbon with four bonds is tetrahedral (sp3 hybridized)

• Carbon with three bonds (one double and two single bonds) is trigonal planar (sp2 hybridized)

• Carbon with two bonds (one triple and one single, or two double bonds) is linear (sp hybridized)

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Hydrocarbons

• Hydrocarbons contain only C and H (nonpolar molecules)Molecules held together by London dispersion forces

insoluble in waterLess dense than waterBP and MP increases with molecular size

• Aliphatic hydrocarbons saturated = alkanes, unsaturated = alkenes or alkynescarbon atoms can attach together in long chains, or they

can attach together to form rings

• Aromatic hydrocarbons

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Saturated Hydrocarbons• Saturated (with hydrogens) hydrocarbons only have

C─C single bonds, sp3 hybridization, are called alkanesStraight chain alkanes, also called normal alkanes, have

the general formula CnH2n+2

Ring alkanes have 2 fewer hydrogens per ring formed and have the general formula CnH2n

8

Unsaturated Hydrocarbons• Unsaturated hydrocarbons have one or more carbon-

carbon double (alkenes, general formula CnH2n) or triple bonds (alkynes, general formula CnH2n-2) remove two H for each double bond remove four H for each triple bond

Aromatic Hydrocarbons• Aromatic hydrocarbons contain a ring structure

that seems to have double bonds, but the compound has enhanced stability vs. alkenes

• The most prevalent and simplest example is benzene (C6H6)

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CnHn

CnH2n+2

CnH2n

CnH2n-2

Uses of Hydrocarbons

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Assuming only chains with a maximum of one unsaturation, decide if each of the following molecular formulas represents an alkane,

alkene, or alkyne

C14H28

C25H52

C12H22

Alkene CnH2n

Alkane CnH2n+2

Alkyne CnH2n-2

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Formulas• Molecular formulas tell you the type and number of atoms

in a molecule, but not how they are attached• Structural formulas show you the attachment pattern • In addition, models show you the shape of the molecule

• The condensed formula lists each central atom and then gives the attached groups directly afterParentheses are used to indicate more than one group

attached to same previous central atom

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Structural formula for the n-Alkane C8H18

• Connect the C atoms in a rowCarbon backbone =

• Add H to give four bonds on each C.middle C gets 2 H’s end C gets 3 H’s

• The condensed formula has the H attached to each C written directly after it. The bonds between carbons are not shown

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Condensed formula for the n-Alkane C8H18

Draw a complete structural formula for CH2CHCH2CH(CH3)CH2CH3

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start by writing the first C with its attached H’scontinue adding each successive C with its

attached H’s or branch chainsafter the entire chain is constructed, apply the rule

4 bonds per C to identify double or triple bonds

Write a complete structural formula for the straight chain isomer of C7H16

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Draw a complete structural formula for CHCCH2C(CH3)2CH3

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Carbon Skeleton Formulas• Only lines drawn, C atoms indicated by a line

intersection or a line end

• H on carbon is omitted from the structureBut included on functional groups

• Multiple bonds are indicated

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Draw a complete structural formula for each of the following

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Isomers: Different Molecules Having the Same Molecular Formula, e.g. C4H10

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• Structural isomers have same number and type of atoms, but different atom attachmentsStructural isomers have different properties

Butane, BP = 0 °C Isobutane, BP = −12 °C

Rotation about a Bond Is NOT Isomerism

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• Stereoisomers are isomers with the same pattern of atom attachments, but the atoms have a different spatial orientation

Possible Structural Isomers

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Example 20.1: Write the structural formula and carbon skeleton formula for C6H14

start by connecting the carbons in a line

determine the C skeleton of the other isomers

fill in the H to give each carbon four bonds

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Example 20.1: Write the structural formula and carbon skeleton formula for the 5 structural isomers of C6H14

convert each to a carbon skeleton formula – each bend and the ends represent C atoms

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n-hexaneBP 69 ºC

2-methylpentaneBP 60 ºC

3-methylpentaneBP 63 ºC

2,2-dimethylbutaneBP 50 ºC

2,3-dimethylbutaneBP 58 ºC

Example 20.1: Write the structural formula and carbon skeleton formula for the 5 structural isomers of C6H14

Draw the three structural isomers of pentane

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• Ring alkanes have higher boiling points than straight chain alkanes (not shown)

• Branched chain alkanes have lower boiling points than straight chain alkanes

Alkane MP and BP

Naming Alkanes/Alkenes & Alkynes

• a “parent”, which indicates the length of the longest carbon chain or # of carbons in a ring

• Each name consists of a “prefix”, which indicates position, number, and type of branches and/or functional groups

• a “suffix”, which indicates the type of hydrocarbon, ane (saturated), ene (unsaturated with double bond), yne (unsaturated with triple bond) and/or the presence of certain functional groups

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Naming Alkanes1. Find the longest continuous carbon chain2. Number the chain from end closest to a branch

if the first branches are equi-distant use next one in

3. Name branches as alkyl groups locate each branch by preceding its name with the

carbon number on the chain

4. List branches alphabetically do not count prefixes such as n-, sec-, t- count iso-

5. Use prefix if more than one of same group present di, tri, tetra, penta, hexa do not count in alphabetizing

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Alkyl Groups

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1. Find the longest continuous C chain and use it to determine the base name

Example – Name the alkane

because the longest chain has 5 Cthe base name is pent- and since this is a saturated

hydrocarbon, it has an –ane ending, pentane30

2. Identify the substituent branches

Example – Name the alkane

there are 2 substituentsboth are 1 C chains, called methyl

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3. Number the chain and substituents

a) determine the end closest to a substituent branch

if first substituent is equi-distant from start as the last one is from the end, refer to next substituent in

b) then assign numbers to each substituent based on the number of the main chain C it is attached to

Example – Name the alkane

both substituents are equi-distant from the end,

no other groups to reference

1 2 3 4 5

2 432

Example – Name the alkane4. Write the name in the following order

a) substituent number of first alphabetical substituent followed by dash

If two of the same group, their numbers are separated by a comma, then followed by the dash

b) substituent name for first alphabetical substituents only, followed by a dash

no dash for last substituent listed use prefixes to indicate multiple identical substituents

c) repeat for other substituents alphabeticallyd) finally, name of main chain

2 4

2,4 – dimethylpentane

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Examples of Naming Alkanes

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3-ethyl-2-methylpentane

Draw and name all ninestructural isomers of heptane

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Draw and name all nine structural isomers of heptane

• Take one C off the right end of the straight chain isomer and attach it to the second C in from the left end Then keep moving it down the chain, but not past the

halfway point

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• Start by drawing the carbon skeleton of the straight chain isomerThe prefix hept- means 7, so the molecular formula is

C7H16

Draw and name all nine structural isomers of heptane

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• Take another C off the right end of 2-methyl isomer and attach it to the third C in from the left end

• Then keep moving it down the chain

• Now reposition that second C substituent to be on the same carbon as the first substituent

• Then keep moving it down the chain

• Take another C off the right end of 2,2-dimethyl isomer and attach it to the third C in from the left end

• Then keep moving it down the chain (not possible here)

• Take a two C chain off the right end of the parent straight chain and attach it to the third C in from the left end (putting it on the second carbon gives a previously identified structure)

• Then keep moving it down the chain, but not beyond halfway

Draw & name all 9 structural isomers of heptaneFind the base name of each main chain

Number the main chain from end closest to a substituent

Name and number the alkyl groups

n-Heptane

Hexanes

Pentanes

Butane38

1 2 3 4 5 6 7

1 2 3 4 5 6 1 2 3 4 5 6

1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

1 2 3 4 51 2 3 4 5

1 2 3 4

n-heptane

2-methylhexane 3-methylhexane

2,2-dimethylpentane 2,3-dimethylpentane 2,4-dimethylpentane

3,3-dimethylpentane

3-ethylpentane2,2,3-trimethylbutane

Alkenes: Aliphatic Unsaturated Hydrocarbons

• Also known as olefins (C=C double bonds)• Formula CnH2n (for 1 C=C)

subtract 2 H for each additional double bond• Trigonal planar shape around carbon, sp2

• Polyunsaturated = many double bonds

• No free rotation around double bond

• Composed of 1sigma and 1 pi () bond

• Not twice as strong as single bond, therefore less stable and more reactive

• Shorter than single bond, longer than triple bond

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Physical Properties of Alkenes

• pi electrons not held as tight as sigma, therefore alkenes are more polarizable than alkanes

• cis isomer generally more polar than transtrans lower boiling point than cistrans higher melting point than cis

molecules are more symmetrical and pack better

• densities similar to alkanes

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produced by ripening fruitused to make polyethylene

used to make polypropylene

Alkynes• Aliphatic, unsaturated, CC triple bond

• sp hybridized, linear shape

• Formula for one triple bond = CnH2n−2

subtract 4 H from alkane for each triple bond

• Internal alkynes have both triple bond carbons attached to C

• Terminal alkynes have one carbon attached to H

• Composed of 2 pi bonds and 1 sigma

• Shorter than C–C and C=C

• Stronger than C–C, but not 3x as strongCC = 836 kJ/mol, C–C = 368 kJ/mol

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Physical Properties of Alkynes

• Higher boiling points than similar sized alkenessimilar size = same number of carbonsmore pi bond = more polarization = higher boiling

point

• Slightly higher densities than similar alkenes

• There are no alkyne cis or trans isomers

• Internal alkynes have higher boiling points than terminal alkyneswith the same number of C

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aka acetylene

Naming Alkenes and Alkynes

• Change suffix on main name from -ane to -ene for base name of alkene, or to -yne for the base name of the alkyne

• Number chain from end closest to multiple bond

• Number in front of main name indicates first carbon of multiple bond

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Examples of Naming Alkenes

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Examples of Naming Alkynes

4-methyl-2-pentyne

Name the Alkene1. Find the longest, continuous C chain that

contains the double bond and use it to determine the base name

Because the longest chain with the double bond has6 C the base name is hexene

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2. Identify the substituent branches

Name the Alkene

there are 2 substituentsone is a 1 C chain, called methyl

the other one is a 2 C chain, called ethyl

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b) then assign numbers to each substituent based on the number of the main chain C it is attached to

Name the Alkene

4-methyl

3-ethyl

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3. number the chain and substituents

a) determine the end closest to the double bond if double bond equi-distant from both ends, number

from end closest to the substituents Find the longest parent chain

4 3 2 1

5 6

3 2 1

4 5

….oops, try again….much better

Name the Alkene4. Write the name in the following order

a. substituent number of first alphabetical substituent – substituent name of second alphabetical substituent – use prefixes di, tri, tetra to indicate multiple identical

substituentsb. repeat step a. for other substituentsc. – number of first C in double bond – name of main

chain with ene ending

3–ethyl–4–methyl–2–hexene

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1234

5 6

4-methyl

2-ene

3-ethyl

hex

Name the following

3,4-dimethyl-3-hexene

12

3 4 5 6

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Did you notice that this is a C Csymmetrical molecule? | | C-C-C-C-C-C

Name the Alkyne1. Find the longest, continuous C chain that

contains the triple bond and use it to determine the base name

Because the longest chain with the triple bond has 7 C the base name is heptyne

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2. Identify the substituent branches

Name the Alkyne

there are 2 substituentsone is a 1 C chain, called methylthe other one is called isopropyl

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Name the Alkyne

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1234567

3. number the chain and substituents

a. determine the end closest to the triple bond if triple bond equidistant from both ends, number

from end closest to the substituents

b. then assign numbers to each substituent based on the number of the main chain C it is attached to

Name the Alkyne4. write the name in the following order

a) substituent number of first alphabetical substituent – substituent name of first alphabetical substituent – use prefixes to indicate multiple identical

substituentsb) repeat for other substituentsc) number of first C in triple bond – name of main chain

4–isopropyl–6–methyl–2–heptyne46

1234567

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Name the Following

3,3-dimethyl-1-pentyne

123

4 5

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Stereoisomers• Stereoisomers are two different molecules whose

atoms are connected in the same order, but with a different spatial orientation. They can be geometric or optical isomersGeometric isomers are stereoisomers that are not

optical isomersBecause the rotation around a double bond is highly

restricted, you will have different molecules if groups are on the same side of the double bond, cis , vs. when the groups are on opposite sides of the double bond, transocalled cis–trans isomerism

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There is Free Rotation Around C─C

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But No Free Rotation for C=C:Cis-Trans Isomerism

Cis-Trans Isomerism

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The cis and trans isomers are

different molecules with different

properties.

Cis–Trans Isomerism is important in nature

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Optical Isomers areNon-superimposable Mirror Images

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• A pair of non-superimposable mirror images is called a pair of enantiomers

• Any molecule with a non-superimposable mirror image is said to be chiral Any carbon with 4 different substituents will be a chiral center

a mirror image cannot be rotated so all its atoms align with the same atoms of the original molecule

Optical Isomers of 3-methylhexane

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Draw the mirror image of the molecule and decide if they are enantiomers

Enantiomers

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Optical Activity• Plane-polarized light is filtered so that only the waves

traveling in a single plane are allowed through

• Enantiomer’s physical properties are identicle, except the direction they rotate plane-polarized light

Each enantiomer will rotate the light plane the same amount, but in opposite directions

dextrorotatory = rotates the plane to the right levorotatory = rotates the plane to the left

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Mixtures of Enantiomers• An equimolar mixture of a pair of enantiomers is called a

racemic mixtureHalf the molecules rotate plane polarized light to the left and

the other half rotates it to the right the rotations cancel, so the racemic mixture does not rotate the

light plane Assuming a pure enantiomer’s rotation is known, a non-racemic

mixture can be analyzed by the percent rotation vs. the pure enantiomer’s rotation

• A pair of enantiomers will have the same chemical reactivity in a non-chiral environment, but in a chiral environment they may exhibit different behaviorsenzymes select only one enantiomer of a pair this behavior is called shape selectivity

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Reactions of Hydrocarbons• All hydrocarbons can be combusted

Combustion is exothermic, releases heat & light energyabout 90% of U.S. energy generated by combustionThe larger the alkane, the more heat is released

2 CH3CH2CH2CH3(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)

CH3CH=CHCH3(g) + 6 O2(g) → 4 CO2(g) + 4 H2O(g)

2 CH3CCCH3(g) + 11 O2(g) → 8 CO2(g) + 6 H2O(g)

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Alkane Substitution Reactions• replace H with a halogen atom

initiated by addition of energy in the form of heat or ultraviolet light to start breaking bonds

get multiple products with multiple substitutions

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Addition Reactions of Alkenes and Alkynes:adding a molecule across the multiple bond

• Adding H2 (Hydrogenation) converts unsaturated molecule to saturated (generally requires a catalyst)

alkene + H2 → alkane OR alkyne + H2 → alkene + H2 → alkane

•Adding X2 (Halogenation)

•Adding HX (Hydrohalogenation) when adding a polar reagent, such as HX, to a double or

triple bond, the positive part attaches to the carbon with the most H’s

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Resonance Hybrid

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• Aromatics contain benzene ring structure

• Though drawn with localized C=C, they do not behave like alkenes

• The true structure of benzene is a resonance hybrid of two structures

Naming Monosubstituted Benzenes• “Substituent name”benzene

halogen substituent = change ending to “o”Alkane group = change ending to “yl”

• but some have common names

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methylbenzeneaminobenzenehydroxybenzenephenylethylene

• When the benzene ring is not the parent, but a substituent, it is called a phenyl group

Naming Disubstituted Benzenes• Number the ring starting at attachment for first

alphabetical substituent, then move toward seconduse “di” if both substituents are the same

• Alternatively, use relative position prefixortho- = 1,2; meta- = 1,3; para- = 1,4

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2-chlorotolueneortho-chlorotoluene

o-chlorotoluene

3-chlorotoluenemeta-chlorotoluene

m-chlorotoluene

4-chlorotoluenepara-chlorotoluene

p-chlorotoluene

Functional Groups• Other organic compounds are hydrocarbons in which

functional groups have been substituted for hydrogens

• A functional group is a group of atoms that have a characteristic influence on the properties of the moleculegenerally, the reactions that a compound will perform are

determined by what functional groups it hasbecause the kind of hydrocarbon chain is irrelevant to the

reactions, it may be indicated by the general symbol R

CH3—OHR group functional group

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Alcohols R—OH• Methanol = CH3OH = wood alcohol from thermolysis of wood

PoisonousUsed in paint solvent

• Ethanol = CH3CH2OH = grain alcohol = fermentation of sugars in grainsAlcoholic beverages (proof number = 2 x % of alcohol)Gas additive

• Isopropyl alcohol = (CH3)2CHOH = rubbing alcohol = 2-propanol

Poisonous

• Main chain must contain OHNumber main chain from end closest to OHAdd ol ending to the base name Use number of C where OH attached in front of nameName as hydroxy group if higher precedence group present

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Naming Alcohols

1 2 3 4 5 6

4-ethyl-4-methyl-3-hex-5-enol

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3-ethyl-1-hexanol

1 2 3

4 5 6

12345

1-pent-4ynol

Reactions of Alcohols

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Nucleophilic substitutionCH3─OH + HCl CH3Cl + H2O

Acid catalyzed elimination (dehydration)

CH3─ CH2OH CH2═CH2 + H2OH2SO4

Oxidation

CH3CH2OH CH3CHO CH3COOH −2 H −2 H

a common oxidizing agent is Na2Cr2O7

Alcohols with very active metals

2 CH3─OH + 2 K 2 CH3O−K+ + H2

Aldehydes and Ketones• Contain the carbonyl group (C=O)• Aldehydes = at least 1 H on C• Ketones = C has two R groups

• Formaldehyde = H2C=Opungent gas formalin = a preservativewood smoke, carcinogenic

• Acetone = CH3C(=O)CH3

nail-polish remover

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• Many aldehydes and ketones have pleasant tastes and aromas

• Some are pheromones

Aldehyde Odors and Flavors

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• butanal = butter

• vanillin = vanilla

• benzaldehyde = almonds

• cinnamaldehyde = cinnamon

• acetophenone = pistachio

• carvone = spearmint

• ionone = raspberries

• muscone = musk

Ketone Odors and Flavors

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Naming Aldehydes and Ketones• Main chain must contain C=O

unless COOH present

• Number main chain from end closest to C=O

• For aldehydes, give base name an “al” ending always on C1

• For ketones, give base name an “one” ending and start numbering from the end closest to the C=O

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4-methyl-3-hexenal

12345

12

34 5

5-hydroxy-3-isopropyl-4-methyl-2-hexanone

6

Reactions• Aldehydes and ketones are generally synthesized by

the oxidation of alcoholsTherefore, reduction of an aldehyde or ketone results in

an alcoholCommon reducing agents are H2 with a Ni catalyst,

NaBH4, and LiAlH4

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Addition to C=O

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polar molecules add across the C=O, with the positive part attaching to O

C=O group is highly polar many reactions involve addition across C=O,

with positive part attached to O

−

Carboxylic Acids - RCOOH

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• Sour tasting• Weak acids• Citric acid

found in citrus fruit

• Ethanoic acid = acetic acidvinegar

• Methanoic acid = formic acidinsect bites and stings

Naming Carboxylic Acids• Carboxylic acid group always on end of main chain

has highest naming precedence of functional groupsalways C1, therefore, position not indicated in name

• Change ending to oic acid

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Synthesis of Carboxylic Acids

• Made by the oxidation of aldehydes and alcohols

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Esters = R–COO–R• Made by reacting carboxylic acid with an alcohol

RaCOOH + RbOH RaCOORb + H2O

• Sweet odor

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Naming Esters• Carboxylic acid ester group always on end of main chain

unless carboxylic acid group presentester group always on C1, so position not indicated in name

• Begin name with alkyl substituent attached to ester O

• Name main chain with oate ending

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• Acid anhydrides are made by the condensation reaction between 2 carboxylic acid molecules

the reaction is driven by heat

R C

O

OH OH C

O

R' R C

O

O C

O

R'

+ + HOH

Condensation Reactions• A condensation reaction is any organic reaction

driven by the removal of a small molecule, such as water

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• Esters are made by the condensation reaction between a carboxylic acid and an alcohol

the reaction is acid catalyzed

Synthesis of Aspirin(Acetylsalicylic Acid)

Ethers = R–O–R

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• Ether = diethyl ether = CH3CH2OCH2CH3

Anesthetic Polar molecules Used as solvents

• To name ethers, name each alkyl group attached to O, then add the word ether to the end

isopropyl methyl ether

Amines• N containing organic molecules

Very bad smellingOrganic basesForm when proteins decompose

• Name alkyl groups attached to the N, then add the word amine to the end

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isopropyl methyl amine

Amines

• Many amines are biologically activedopamine – a neurotransmitterepinephrine – an adrenal hormonepyridoxine – vitamin B6

• Alkaloids are plant products that are alkaline and biologically active toxicconiine from hemlockcocaine from coca leavesnicotine from tobacco leavesmescaline from peyote cactusmorphine from opium poppies

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Amine Reactions• Weak bases

react with strong acids to form ammonium salts

RNH2 + HCl → RNH3+Cl−

• React with carboxylic acids in a condensation reaction to form amides

RCOOH + H—NHR’ RCONHR’ + H2O

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Polymers

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Macromolecules• Polymers are very large molecules made by repeated

linking together of small molecules monomers

• Natural polymers are polymers found in both the living and nonliving environment

• Modified natural polymers are natural polymers that have been chemically altered

• Synthetic polymers are polymers made in a lab from one, two, or three small molecules linked in a repeating pattern plastics, elastomers (rubber), fabrics, adhesives

• Composites are materials made of polymers mixed with various additives additives such as graphite, glass, metallic flakes

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Natural Polymers• Polysaccharides – polymers made of repeating small sugar

molecule units cellulose (cotton) starch

• Proteins – polymers made of repeating amino acid units• Nucleic acids (DNA) – polymers made of repeating nucleotide units

• Natural latex rubber – polyisoprene• Shellac – a resin secreted by lac bugs• Gutta-percha – a polyisoprene latex from the sap of the gutta-

percha plant used to fill space for root canal

• Amber, lignin, pine rosin – resins from trees• Asphalt – polymeric petroleum

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Modified Natural Polymers

• Cellulose acetate – an ester of cellulose and acetic acid rayon film

• Vulcanized rubber – latex rubber hardened by cross-linking with sulfur

• Nitrocellulose – an ester of cellulose with nitric acid gun cotton celluloid

ping-pong balls

• Casein – a polymer of the protein casein made by treating cow’s milk with acid buttons, mouldings, adhesives

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Polymerization

• Polymerization is the process of linking the monomer units together

• There are two processes by which polymerization may proceed – addition polymerization and condensation polymerization

• Monomer units may link head-to-tail, or head-to-head, or tail-to-tail during polymerizationhead-to-tail most common regular pattern gives stronger attractions between

chains than random arrangements

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Addition Polymerization

• Monomers add to the growing chain in such a manner that all the atoms in the original monomer wind up in the chainno other side products formed, no atoms

eliminated

• First monomer must “open” to start reactiondone with heat, or the addition of an initiator

• The process is a chain reactioneach added unit ready to add another

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Addition Polymerization of Vinyl Chloride

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Condensation Polymerization

• Monomer units are joined by removing small molecules from the combining unitspolyesters, polyamides lose water

• No initiator needed

• The process is a chain reaction

• Each monomer has two reactive ends, so chain can grow in two directions

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Condensation Polymerization

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Plastics• Plastics are polymer materials capable of being

molded or shaped.Round, hard balls; thin, flexible threads; intricate

molds; or flat sheets.• Plastics have molar mass from 10,000 to

1,000,000 amu• Many plastics are in the “glass” or amorphous

solid statesolid that has semi-fluid characteristicsglass transition temperature is where an

amorphous polymer is converted between rubbery and glassy states

plastics do not melt like an ice cube, they rubberize

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Characteristics of Plastics• Transparent or translucent• Chemical resistance• Thermal and electrical insulators• Low density• Varying strengths

Kevlar• Mold or extrude• Elasticity

regain original shape if quick stress applied• Foamed• Tend to soften when heated

rather than quickly melt

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Synthetic PolymersPolyethylene – HDPE & LDPE

Polypropylene

Polyvinyl chloride

PolyamidesnylonKevlar

Polyesterspolyethylene terephthalate

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1

Polyethylene Terephthalate (PET)

• Condensation copolymer of ethylene glycol + terephthalic acidA polyester

• Transparent

• High-impact strength

• Nonreactive with acid and atmospheric gases

• Doesn’t stretch

• Used for soda bottles, Dacron, Mylar

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2

High Density Polyethylene (HDPE)• Addition polymer with linear chains• Opaque• Denser than LDPE• Mechanically stronger than LDPE• More rigid than LDPE

more crystalline• Higher heat resistance than LDPE• Nonreactive to acids and bases• Absorbs oils and softens• Oxidizes on exposure to air and sunlight• Subject to cracking• Used for containers, caps, bullet-proof vests,

synthetic ice106

3

Poly Vinyl Chloride (PVC)

• Addition polymer• Transparent to opaque• Flame resistant• Low heat resistance• Good chemical resistance• High-impact strength• Quite rigid• Many additives used to modify properties

plasticizer adds flexibility• Used in food wrap, pipes, flooring and wall

covering, toys, hoses, auto trim, squeeze tubes, and appliance housings

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4

Low Density Polyethylene (LDPE)

• Addition polymer with branched chains

• Lower density, strength, heat resistance (100–125 °C), and rigidity than HDPE

• Used in food, trash, and grocery bags as well as in electrical wire insulation

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5

Polypropylene (PP)• Addition polymer

• Opaque

• High stretching strength

• High heat resistance (170 °C)

• Excellent chemical resistance

• Flexed almost indefinitely without tearing

• Smooth surface with high luster

• Used in carpets and upholstery; chemical resistant pipes, containers, and tanks; margarine tubs; and medicine bottles

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6Polystyrene (PS)

• Addition polymer

• Low-impact resistance

• Fair strength and stiffness

• Poor chemical resistance

• Transparent, glassy, sparkling clarity

• Moderate heat resistance (90 °C)

• Used in model cars, computer housing, Styrofoam, clear drinking cups, and hard-molded parts

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Acrylics

• Polymethylmethacrylate, PMMA• Low-impact resistance• Good strength and stiffness• Excellent transparency• Excellent scratch resistance• Moderate heat resistance• Addition polymer of methyl methacrylate• Uses include Plexiglas, Lucite, lighting fixtures,

lenses, fiber optic filament, appliance faceplates, decorative signs, and paints

• Also, reduces oil viscosity

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Polycarbonates (PC)• Excellent physical properties

• Excellent toughness

• Very good heat resistance

• Fair chemical resistance

• Transparent

• Condensation copolymer of Bisphenol A and phosgene

• Lexan, Calibre , Makrolon , Panlite

• Used in equipment housings, exterior auto parts, outdoor light fixtures, non-auto vehicle windows, structural parts, medical supply parts, scratch-resistant coatings, eye wear, bullet-proof glass, and DVDs

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Nylon• Condensation copolymer of a diamine with a diacid

polyamidesnylon 6,6

made by condensing 1,6–hexandiamine, H2N–(CH2)6–NH2, with hexandioic acid, HOOC–(CH2)4–COOH

• Good physical propertiesaffected by moisture

• Very good heat resistance• Excellent chemical resistance• Excellent wear resistance

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