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Organic Chemistry
1. Organic Chemistry
- Organic chemistry is the study of carbon compounds.
- The properties of organic compounds are determined by two factors:
i.
A molecular skeleton called a hydrocarbon. This is a series of carbon atoms
linked together to form a stable framework that is almost completely unreactive.
The unbonded electron positions are then filled (saturated) with hydrogen atoms.
ii.
A series of different reactive groups, called functional groups, can then be added.
They determined the basic “chemistry” of the molecule.
- Carbon atoms have unique properties that allow them to make many compounds:
i.
Carbon atoms can form four bonds ( C )
ii.
They link together with covalent bonds to form chains and rings of different sizes,
C C
C
Electron dot formula
iii.
C C C
structural formula
They form single, double and triple covalent bonds.
C C C
C C C
C C C
- Hydrocarbons tend to have some unique properties that are determined by their covalent
bonds:
i.
Hydrocarbons are easily decomposed by heat.
ii.
Hydrocarbons reactions are generally slow.
iii.
Most hydrocarbons are insoluble in water. Their molecules are nonpolar and are
not attracted to the polar water molecules.
2. Alkanes
a) Continuous –Chain Alkanes
- The simplest hydrocarbons are the alkanes that contain only hydrogen and carbon atoms
with atoms with single covalent bonds.
H H
→ H C C H
H H
- The formula for and alkane can be given several ways:
C5H12 (molecular formula)
H H H H H
1) H-C – C – C – C – C – H
(complete structural formula)
2 C
H
+
H
6H
H H H
2
2) CH3-CH2-CH2-CH2-CH3
3) C-C-C-C-C
4)
(condensed structural formula or semi-structural)
(skeletal structural formula)
(line structural formula)
- The simplest alkanes form a chain. The first ten compounds in this homologous series
are to be memorized:
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CH4 Methane
2 C2H6
Ethane
3 C3H8 Propane
4 C4H10 Butane
5 C5H12 Pentane
6 C6H14 Hexane
7 C7H16 Heptane
8 C8H18 Octane
9 C9H20 Nonane
10 C10H22 Decane
Note:
i.
The names for the alkanes end in “-ane”.
ii.
The general formula for alkanes is CnH2n+2
b) Branched – Chain Alkanes
- Sometimes and atom or group of atoms can replace a hydrogen atom in an alkane. The
added atom is called a substituent.
CH3-CH2-CH3 → CH3-CH(Br)-CH3
If the substituent is another hydrocarbon, it is called and alkyl group.
CH3-CH2-CH3 → CH3-CH(CH3)-CH3
An alkyl group (methyl) joined to the parent chain (propane)
-When an alkyl group is attached to a parent chain, it creates a branched-chain alkane.
The names of the alkyl groups are based on its alkane name but ending in “yl”.
Examples:
Methyl (-CH3)
Ethyl (-CH2-CH3) or (-C2H5)
Propyl (-CH2-CH2-CH3) or (-C3H7)
Note:
i.
An alkyl group cannot exist by itself; it must be attached to some molecule.
ii.
The general formula for alkyl groups is CnH2n+1
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Example: CH3-CH2-CH-CH2-CH3
CH2
CH2-CH3
This shows an ethyl group attached to a heptane molecule.
The formula can also be given as CH3-CH2-CH2-CH(C2H5)-CH2-CH2-CH3
Nomenclature for Branched-Chain Alkanes
1. For One Branch
1. Find the longest chain and name it.
2. Number the carbons in order to locate the alkyl group. (Begin from the end that
gives the branch the lower number).
3. The alkyl group name is placed in front of the parent chain name.
4. The number must be separated from the name with a hyphen.
Example: CH3-CH2-CH2
- longest chain = hexane
CH-CH2-CH3
- branch name = methyl
CH3
- branch location = 3rd atom
NAME: = 3 - methylhexane
2. For More Than One Branch
- Each branch is again located on the main chain.
- The branch names are listed alphabetically.
- Prefixes are used if an alkyl group appears more than once.
Example: CH3-CH2-CH2
CH-CH3
- longest chain = octane
- branches
= methyl at 4 and 5
= ethyl at 4
CH3-C-CH2-CH3
CH2-CH2-CH3
NAME: = 4-ethyl-4,5-dimethyloctane
Note:
i.
Branches can be identified in condensed formulas by placing them in brackets.
From the previous example (4-ethyl-4,5-dimethyloctane)
CH3-CH2-CH2-CH(CH3)-C(CH3)(C2H5)-CH2-CH2-CH3
ii.
Don’t forget: Count from the end that gives the lowest numbers
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2c) Structural Isomers
- It is possible to draw the structures of two or more hydrocarbons that have the same
molecular formula but different structural formulas. These compounds are called
structural isomers.
C4H10
CH3-CH2-CH2-CH3
butane
CH3-CH(CH3)-CH3
2-methylpropane
- Isomers will only be a different chemical only if they can be given a different name.
- Isomers have different chemical and physical properties.
Try This:
1. How many structural isomers are possible for each of the first five straight-chain
alkanes.
2. Give the condensed structural formula and name for
a) all of the isomers for C5H12
b) the five isomers of C6H14
3. Optional Challenge – Name all 18 isomers of C8H18.
3. Alkenes and Alkynes
- Remember that carbon can also form multiple bonds. Hydrocarbons containing a double
bond are called alkenes
( C=C ).
- Alkenes are unsaturated hydrocarbons because they contain fewer hydrogen atoms.
These atoms were removed in order to create the double bond.
- The other unsaturated hydrocarbon is the alkyne which contains a triple bond ( -C≡C- ).
Nomenclature:
1. Find the longest chain containing the multiple bonds (Its name will now end in “ene” or “-yne”).
2. The main chain must now be numbered to give the multiple bonds the lowest
number (instead of the branched chains). This number will be used in front of the
name of the main chain.
CH3-CH=C(CH3)-CH(CH3)-CH3
(3,4-dimethyl-2-pentene)
CH3-CH2-CH(C2H5)-C≡CH
(3-ethyl-1-pentyne)
Note:
i.
The general formula for an alkene is CnH2n and for an alkyne is CnH2n-2.
ii.
The physical properties of the unsaturated substances are similar to those of the
alkanes.
iii.
The most important difference in chemical properties is that multiple bonds are
quite reactive.
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Try This: Name or provide the structural formula for these compounds:
i.
CH3-C(CH3)=CH-CH(CH3)-CH3
ii.
CH3-CH2-CH(C2H5 )-C≡CH
iii.
5,6-dimethyl-2-octyne
iv.
2-methyl-1-propene
Summary
Number
of C
1
2
3
4
5
6
7
8
9
10
Name of
the
prefix
for
Meth
Eth
Prop
But
Pent
Hex
Hept
Oct
Non
Dec
Hydrocarbons
molecule alkane
CnH2n + 2
Hydrocarbons
molecule alkene
CnH2n
Hydrocarbons
molecule alkyne
CnH2n -2
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
nil
C2H4
C3H6
C4H8
C5H10
C6H12
C7H14
C8H16
C9H18
C10H20
nil
C2H2
C3H4
C4H6
C5H8
C6H10
C7H12
C8H14
C9H16
C10H18
4. Cycloalkanes (Geometric Shapes)
- In some alkanes, the two ends of the chain have attached to form a ring. These are
called cycloalkanes.
Examples:
1) cyclobutane
2) cyclohexane
H2C – CH2
H2
C
H2C – CH2
H2C
CH2
or
or
H2C
CH2
C
H2
Note:
i.
Cyclohexanes have only single bonds and that there general formula is CnH2n.
Cycloalkenes and cycloalcynes also exist.
ii.
Cycloalkanes have strained bonds that lead to a less stable molecule than its
equivalent alkane.
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Nomenclature: The ring carbons are numbered so as to give the substituents the lowest
possible number (One substituent will always be 1).
CH2CH3
CH3
H3C
CH3
1,3-dimethylcyclooctane
1-ethyl-2-methylcyclopropane
Try This: Give the structural formula for these compounds.
a) 1-ethylcyclobutane
b) 1,3-dimethylcyclopentane
c) 1,1-dimethylcyclopropane
d) cyclopropylcyclohexane (!)
5) Benzene
- The most important group of cyclic hydrocarbons is the aromatic compounds, the
simplest of which is benzene (C6H6). After benzene forms a ring, each carbon atom has
one extra electron that is free to make half of a double bond.
HC
CH
HC
CH
C
H
HC
⇔
HC
CH
C
H
C
H
The benzene ring can be shown as
CH
C
H
or
Resonance occurs when two valid structures can be drawn for the same molecule.
Resonance is the result of the combination of blending of the two possible structures. The
actual substance is an average of all the possible arrangements.
Molecules that exhibit resonance are very stable.
Nomenclature:
1) One substituent Added:
(branch)
CH3 or C6H5(CH3)
Methylbenzene (or toluene)
2) When Used as a Substituent – named phenyl (-C6H5) *(CnHn-1)
CH3-CH-CH2-CH3 or CH3-CH(C6H5)-CH2-CH3
2-phenylbutane
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3) Two Substituent Added (note the positions)
H3C
CH3
H3C
H3C
CH3
1,2-dimethylbenzene
or
o-dimethylbenzene
(“ortho” position)
1,3-dimethylbenzene
or
m-dimethylbenzene
(“meta” position)
CH3
1,4-dimethylbenzene
or
p-dimethylbenzene
(“para” position)
Note: that one Substituent must be in the “l” position.
6 a) Fractional Distillation
Directions: Use the key words and phrases with its matching step in the diagram to give a
step-by-step explanation of the fractional distillation of oil.
Tower
a) Crude oil, fraction, alkanes
b) Heater, 350oC, boiling point, vaporizing
c) Bubble cap, rising gases, condensation, trays
Fractions
1.
2.
3.
4.
5.
6.
Residue, (tars, asphalt), highest boiling point (400oC), >C30
Lubricants and waxes, 3500C, approximately C20 – C30
Heating/diesel oil, 250oC, C16 – C20
Kerosene, 180oC, approximately C12 – C16
Gasoline, 110oC, approximately C5 – C12
Natural gases, lowest boiling points, C1 – C4, LPG
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6 b) Hydrocarbon Reaction
1. Cracking
Large fractions form the fractionation process is chemically broken with heat and a
catalyst to produce more valuable fuel hydrocarbons with 5-12 carbon atoms per
molecule.
Large molecule → small molecules
Example:
C17H36 → C8H18 + C9H18
alkane alkene
2. Reforming
This is the opposite of cracking. It can convert low-grade gasolines into higher grades
with the use of heat and a catalyst. Small molecules → large molecule
Example:
2 C5H12(l) → C10H22(l) + H2(g)
3. Combustion
Most hydrocarbons are used as fuels (95%).
Hydrocarbon + O2(g) → CO2(g) +18H2O(g) + heat
Example:
2C8H18 + 25O2 → 16CO2 + 18H2O + heat
4. Hydrogenation
This process converts unsaturated hydrocarbons to saturated ones.
Alkene + H2(g) → alkane
Alkyne + H2(g) → alkene
Example:
CH2=CH-CH2-CH3(g) + H2(g) → CH3-CH2-CH2-CH3(g)
1-butene
butane
Try This:
1. Identify and complete each reaction. You must not break the Law (of
Conservation of Matter)
a) C14H30 into octane b) ethane into octane c) 1-octene into octane d) 1-octyne into octane
2. Show the complete combustion of:
a) pentane b) hexane c) hexene
7. Functional Groups
- The hydrocarbon skeleton of an organic molecule is chemically inert. Most organic
chemistry, then, involves the atoms and molecules that are attached to this main chain.
a) Structures
- Functional groups are the atoms in an organic compound that have been added to a
hydrocarbon chain. They are the only part of the molecule that is capable of reacting
chemically.
- Compounds are classified according to their functional groups. Since these groups can
be attached to any chain, we will represent the inert hydrocarbon chain with “R”.
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Family Name
Condensed Formula
Example (3C’s)
General Formula
1. Halocarbons
R(X)
CH3-CH2-CH2(Cl)
CnH2n+1X
2. Alcohols
R(OH)
CH3-CH2-CH2(OH)
CnH2n+2O
3. Ethers
R1 – O – R2
CH3-O-CH2-CH3
CnH2n+2O
4. Aldehydes
R – C(=O)H
CH3-CH2-C(=O)H
CnH2nO
R1 – C(=O) – R2
CH3-C(=O)-CH3
CnH2nO
5. Carboxylic acids
R – C(=O)(OH)
CH3-CH2-C(=O)(OH)
CnH2nO2
6. Esters
R1 – C(=O) – O – R2
CH3-C(=O)-O-CH3
CnH2nO2
7. Polymers
( - R1 – R2 - )n
(-CH2-CH2-CH2-)n
Ketones
Questions:
1. Why does oxygen have to bond twice in a molecule?
2. How many times would these atoms bond? a) S b) Cl c) N d) F e) P
3. Which families cannot be made from methane?
4. Do any groups have the same general formula?
b) Two Physical Properties
- The presence of a functional group has a major effect on the physical properties of a
compound. Intermolecular forces determine many physical properties, such as solubility
and boiling point:
- hydrocarbons – have only weak dispersion forces.
- functional groups – may have strong hydrogen bonds.
- Remember that hydrogen bonds are created between two molecules:
- One molecule contains a hydrogen atom bonded to a highly electronegative
atom (especially oxygen). These hydrogen atoms now can be considered to be
a naked proton (+).
- The other molecule will be polar with a δ- section (especially on oxygen).
The hydrogen bonding, then, occurs between two highly polar molecules.
- Boiling Points: Compounds with hydrogen bonding have higher than expected boiling
points: at SATP, C2H6 = gas but CH3OH = liquid.
- Solubilities: Compounds with hydrogen bonds are usually soluble in water (a polar
molecule): C6H14 = insoluble in water but C5H11OH = soluble in water.
Solubility decreases, as the molecule gets longer. (C12H25OH =slightly soluble in water).
This is because the hydrogen bonding –OH group has less effect on the larger molecule.
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8. 1. Halocarbons (R – X)
- Halocarbons are produced by the substitution of a halogen (Family VIIA) for hydrogen
in the hydrocarbon chain;
Cl = chloro Br = bromo I = Iodo F = Fluoro
as well as
NO2 = nitro NH2 = amino
Nomenclature: The halocarbon is treated as a substituent. Don’t forget that substituents
are named alphabetically.
CH3-C(Br)(CH3)-CH3
2-bromo-2-methypropane
CH3-CH(Cl)-C(NO2)(C2H5)-CH2-CH3
2-chloro-3-ethyl-3-nitropentane
Try This: Name or provide the formula for the following:
a) CH3-CH2(I)
f) trichloromethane
b) CH2(Cl)-CH2(Cl)
g) 2-chloro-3-iodo-1-butene
c) CH(F)(F)-CH(Cl)(Cl)
h) 1,5-dinitro-2-pentyne
d) CH3-CH2-C≡C-CH2(NH2)
i) 1,3-difluorocyclopentane
e) CH3-CH(NO2)-CH2(Br)
j) 1,3-dibromo-3-phenylhexane
Reactions:
a) Addition Reactions – A halogen (X) is added to an unsaturated hydrocarbon at the
double/triple bond. These reactions are quite rapid because there are no strong
covalent bonds to be broken.
R1 = R2 + X2 → RX – RX
Ethyne + chlorine gas → 1,2-dichlorethane
CH≡CH + Cl2 → CH(Cl)=CH(Cl) which can be further reacted
CH(Cl)=CH(Cl) + Cl2 → CH(Cl)(Cl)-CH(Cl)(Cl)
b) Substitution Reactions – A halogen replaces hydrogen in a saturated hydrocarbon.
These reactions occur quite slowly at room temperature because C – H bonds are
quite stable.
R – H + X2 → R – X + HX
Ethane + chlorine → chloroethane + hydrogen chloride
C6H6 + Cl2 → C2H5Cl + HCl
More complicated molecules will form isomers.
CH2(Cl)-CH2-CH2-CH3 + HCl
CH3-CH2-CH2-CH3 + Cl2
CH3-CH(Cl)-CH2-CH3 + HCl
c) Elimination Reactions – This is the most common method for preparing alkenes.
A halocarbon reacts with a hydroxide to produce an alkene.
R – R – X + OH- → R = R + H2O + XCH3-CH(Br)-CH3 + NaOH → CH2 = CH-CH3 + H2O + NaBr
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9. 2. Alcohols
- Alcohols contain the hydroxyl (-OH) group: R – O – H
Nomenclatrue: Add “-ol” to the stem of the name of the parent chain. Number the
position of the hydroxyl group.
If more than one –OH group is present, use these endings:
- “-diol” (two hydroxyls)
- “-triol” (three hydroxyls)
Examples:
CH3-CH(OH)-CH3
2-propanol
CH3-CH(CH3)-CH2-CH2(OH)
3-methyl-1-butanol
CH2(OH)-CH2-CH(OH)-CH3
1,3-butandiol
Phenols are alcohols in which the –OH group is attached to benzene.
OH
[C6H5(OH)]
Try This: Name or give the formulas for the following:
1. CH3CH(OH)-CH3
5. 2-pentanol
2. CH2(Cl)-CH(OH)-CH3
6. 2,2,4-pentatriol
3. CH2(OH)-CH2(OH)-CH2-CH3
7. 3-ethyl-2-pentanol
4. C6H4(OH)(CH3)
8. 2-ethylphenol
Reactions:
1. MAKING ALCOHOLS
i. Fermentation – producing ethanol from sugars by the action of yeast.
C6H12O6(aq) → 2CH3CH2OH(aq) + 2CO2(g)
ii. Substitution – the halogen in a halocarbon is replaced by a hydroxide.
R – X + M – OH
→ R – OH + MX
CH3-CH2(Cl) + NaOH
→ CH3-CH2(OH) + NaCl
iii. Addition – a water molecule (H-OH) is combined with an unsaturated hydrocarbon.
R1 = R2 + H – OH
→ R(OH) \
CH2=CH2 + H-OH
→ CH3-CH2(OH)
i.
2. REACTING ALCOHOLS
Elimination – Alcohols can be used to make alkenes when catalyzed by
concentrated sulfuric acid
acid
R – OH → R1 = R2 + H – OH
CH3-CH2(OH) → CH2=CH2 + H2O
Properties: Alcohols tend to have high boiling points due to the strong hydrogen
bonding that occurs between these molecules.
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- Smaller molecules are also soluble in water as they can hydrogen bond with the polar
water molecules.
- Longer chain molecules tend to be insoluble as the hydroxyl group has less effect on the
molecule. They can be good solvents for nonpolar molecular compounds (“like dissolves
like”).
Try This:
1. Write a balanced equation for the following situations:
a) reacting 2-iodopropane with Ca(OH)2
b) making 1-butene from 1-butanol
c) making 1-propanol from propene
2. Why does wine bubble as it is fermenting?
10. 3. Ethers
- These are compound in which oxygen is bonded between two carbon groups.
O
R1
Properties:
Halocarbons
Ethers
Alcohols
R2 Notice that this is actually a bent molecule.
Summary of Hydrogen Bonding
Hydrogen
donor
X
X
√
Hydrogen
acceptor
X
√
√
Boiling point
increases
Solubility
increases
Nomenclature: The two-alkyl groups are named in alphabetical order and followed by
the word “ether”.
CH3-CH2-CH2-O-CH3
CH3-CH2-O-CH2-CH3
methylpropyl ether
diethyl ether
Try This:
1. The molecular formula C3H8O can represent either two alcohols or an ether. Give
their formulas and names.
2. Would an ether be soluble in a) a halocarbon? b) an alcohol?
11. 4. Aldehydes and Ketones
- These two families share certain structural features and chemical properties.
- They both contain the carbonyl group
C = O, which we will show as (-C(=O)-) in
O
our condensed formulas.
- Aldehydes = chain + carbonyl group + hydrogen = R – C – H
O
- Ketones = chain 1 + carbonyl group + chain 2 =
R1 – C – R2
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Nomenclature:
Aldhydes: change the “_e” ending to “_al”
O
H–C–H
CH3-CH2-CH(=O)
methanal
propanal
Ketones: count the total number of carbons present. Change the “_e” ending to “_one”.
Number the carbonyl location.
O
CH3-C-CH3
propanone
CH3-CH2-C(=O)-CH2-CH2-CH3
3- hexanone
Properties: - They have low boiling points because they have no O – H bonds for
hydrogen bonding.
- When added to water, though, they can hydrogen bond to the water molecules so they
are quite soluble in water.
Try This: Draw and name the aldehyde and the ketone with the molecular formula of
C4H8O.
12. 5. Carboxylic Acids
- These organic acids contain the carboxyl functional group, -C(=O)-OH which include
both the carbonyl group and the hydroxyl group. In molecular formulas, the carboxyl
group is often presented as –COOH.
Properties: Carboxylic acids create the sour taste in foods and have distinctive odors.
- They are polar molecules and are both hydrogen acceptors and hydrogen donors. Thus
they will readily form hydrogen bonds, and smaller molecules are easily dissolved in
water.
- They have all of the properties of acids – react with metals, make indicators change
color, etc.
Nomenclature: Replace the “_e” ending with “_oic acid”.
structural formula
O
CH3-CH2-C-OH
propanoic acid
molecular formula
condensed formula
C2H5COOH
CH3-CH2-C(=O)-OH
Reactions: 1. Fermentation: glucose → ethanol → ethanoic acid
(grape juice) (wine)
(vinegar)
2. They undergo typical acid reactions (neutralization, for example) but at a slower rate.
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Try This:
1. Name a) CH3-CH2-CH2-C(=O)OH b) CH3-C(CH3)(CH3)-C(=O)OH c) COOH
2. Give the formula for a) hexanoic acid b) 3-methylpentanoic acid
3. Use the example to write a balanced equation for the organic reaction:
a) KOH + HCl → KCl + HOH
KOH + CH3-COOH → ?
b) 2Na + 2HCl → 2NaCl + H2
Na + CH3COOH → ?
13. 6. Esters (Acid + Alcohol → Ester)
- Esters are derivatives of carboxylic acids in which the – OH of the carboxyl group has
been replaced by an – OR from an alcohol.
O
R1-C
or
R1COOR2
or
R1-C(=O)-O-R2
O-R2
Reactions: Esters are prepared by combining a carboxylic acid with an alcohol in a
process called esterification:
O
O
R1-C
+
HO-R2 → R1-C
+ HOH
OH
O-R2
carboxylic acid
alcohol
ester
water
Nomenclature: The name of an ester has two parts:
i.
Locate the alcohol branch and name it as an alkyl group.
ii.
Locate the acid branch. The ending of the acid name is changed from “_oic acid”
to “_oate”
O
alcohol
acid
CH3-C
CH3-CH2-C(=O)-O-CH2-CH3
O-CH3
methyl ethanoate
ethyl propanoate
Properties: -Esters are “odor” chemical (fruits and flowers).
- are added to foods to enhance taste + odor.
Try This: Give the esterification reaction (with formulas and names) for
i.
Propanoic acid and butanol
ii.
Butanoic acid + propanol
iii.
Ethanol and methanoic acid
14. 7. Polymerization
- A polymer is a giant molecule formed by the covalent bonding together of repeating
smaller molecules called monomers.
…….. + monomer + monomer + …….. → polymer
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- One method of creating these polymers by addition polymerization – the joining
together of unsaturated (multiple bond) monomers.
If A = the monomer, the polymer will appear as -A-A-A-Acatalyst
n CH2=CH2 → (-CH2-CH2-)n
ethane (ethylene)
polyethylene
catalyst
n CH3CH=CH2 → (-CH2(CH3)-CH2-)n
propene (propylene)
polypropylene
- A condensation polymer is formed by reacting two different compounds together. In
order to do this, a small molecule (usually water) must be split off from the functional
groups.
If A = first monomer and B = second monomer, then the polymer will appear as
-A-B-A-BHere is a general example:
HO-X-OH + HO-Y-OH → (-O-X-O-Y) + 2H2O
“di” acid or “di” alcohol
Note: polyethylene = ice cream plastic containers,
polypropylene = nylon rope
Try This: Write the formula for the following polymers, which were formed by addition
polymerization.
1. Polyvinyl chloride (PVC) which is made form chloroethane.
2. Teflon which is made form tetrafluoroethene.