Chemistry and Chemical Reactivity 1
6th Edition
John C. Kotz
Paul M. Treichel
Gabriela C. Weaver
CHAPTER 11
Carbon: More than Just Another Element
Lectures written by John Kotz
©2006
2006
Brooks/Cole
Thomson
©
Brooks/Cole
- Thomson
ORGANIC CHEMISTRY
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3
cinnamaldehyde
eugenol
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4
Types of Organic Compounds
• Vast majority of over 20 million known
compounds are based on C: organic
compounds.
• Generally contain C and H + other elements
• Great variety of compounds
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Isomerism
• Isomers have identical composition but
different structures
• Two forms of isomerism
– Constitutional (or structural)
– Stereoisomerism
• Constitutional
– Same empirical formula but different atomto-atom connections
• Stereoisomerism
– Same atom-to-atom connections but
different arrangement in space.
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6
Structural Isomers
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Stereoisomers: Geometric
Geometric isomers can occur when there is a
C=C double bond.
Cis-2-butene
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Trans-2-butene
8
Stereoisomers: Optical
• Optical isomers are molecules with
non-superimposable mirror images.
• Such molecules are called CHIRAL
• Pairs of chiral molecules are
enantiomers.
• Chiral molecules in solution can rotate
the plane of plane polarized light.
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Chiral Compounds—Polarized Light
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Stereoisomers Isomers
Chirality
generally occurs
when a C atom
has 4 different
groups attached.
Lactic acid
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Stereoisomers Isomers
Lactic acid isomers are
nonsuperimposable
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Chirality: Handedness in
Nature
These molecules are non-superimposable
mirror images.
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Chirality: Handedness in
Nature
These amino acids are nonsuperimposable mirror images.
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Stereoisomers in Nature
Right- and lefthanded seashells
The DNA here is
right-handed
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15
The egg cases of the
whelk have a righthanded twist.
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Hydrocarbons
• Compounds of C and H
• Subgroups:
– Alkanes: C-C single bonds
– Alkenes: C=C double bonds
– Alkynes: carbon-carbon triple
bonds
– Aromatic: based on benzene
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17
Hydrocarbons
• Alkanes have the general formula
CnH2n+2
• CH4 = methane
• C2H6 = ethane
• C3H8 = propane
• C4H10 = butane
• C5H12 = pentane
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Methane Hydrate, CH4(H2O)x
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A colony of
worms on an
outcropping of
methane
hydrate on the
ocean floor.
See the
interchapter
“The Chemistry
of Fuels and
Energy Sources”
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CH 3CH2 CH 2CH2 CH 3
Pentane
Hydrocarbons
& Structural
Isomerism
21
CH3
CH 3CHCH 2CH3
2-Methylbutane
CH3
H3CCCH3
CH3
2,2-Dimethylpropane
Note names of isomers
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Isomers of C5H12?
C5H12 has 3
structural isomers.
C6H14 has 5
C7H14 has 9
22
Hydrocarbons: Alkanes
Alkanes are colorless gases, liquids,
and solids
Generally unreactive (but undergo
combustion)
Not polar (or low polarity) and so are
not soluble in water.
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Hydrocarbons: Cycloalkanes
All compounds are flexible.
Cyclohexane, C6H12, has interconverting
“chair” and “boat” forms.
Axia l H ato m
H
H
4
H
H
Eq u ator ia l H
a tom
H
5
6
2
3
H
H
H
H
1
HH
Chair form
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H
H
1
H
6
5
H
3
H
2
H
H
H
H
H
H
H
Boat form
H
H
H
H
5
4
H
3
HH
H
H
1
6
H
H
2
H
Chair form
H
24
Alkenes: Compounds with
C=C Double Bonds
• How many isomers are possible for a
compound with the formula C4H8?
3 4
CH2CH3
H
1
C
H
1
C
2
C
H
3
CH3
H
1-butene
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H
1
H3C
2
C
4
CH3
2
C
CH3
2-methylpropene
(isobutene)
H
4
CH3
H
3
C
2
C
H
cis-2-butene
1
H3 C
3
C
H
trans-2-butene
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Alkenes—
Many Occur Naturally
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Reactions of Alkenes:
ADDITION REACTIONS
• Alkenes are unsaturated — more
bonds can form to the C atoms
• Molecules such as Br2, H2, HCl, HBr, and
H2O add to the double bond
H
C C + Br2
H
H
H
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Br Br
H C C H
H H
1,2-dibromoethane
An Addition Reaction
Fat placed
in Br2 vapor
• The fat in bacon is partially unsaturated.
The fat adds Br2 to the C=C bonds.
• Fats can be “hydrogenated” with H2.
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An Addition Reaction
Fat placed
in Br2 vapor
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An Addition Reaction
• Fats can be “hydrogenated” with H2.
Peanut butter has partially hydrogenated
vegetable oil.
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30
CH3(CH2)7CH=CH(CH2)7CO2H
Trans Fatty Acids
tend to raise total blood
cholesterol
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Trans Fatty Acids
Food Percentages of TransFatty Acids
Butter
Soft Margarine
Hard Margarine
Vegetable Oils, Including
Safflower, Sunflower, and Soy
Beefburger, Fried or Grilled
Chocolate Cake with Icing
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3.6
5.2
12.4
0
0.8
7.1
Alkynes
• Alkynes have carbon-carbon triple bonds.
• C2H2: common name = acetylene
systematic name = ethyne
Preparation:
CaC2(s) + H2O(liq) -->
C2H2 (g) + Ca(OH)2(s)
∆Hfo(C2H2, g) = +226.7 kJ/mol
∆Hrxn for C2H2 + O2
= –1300 kJ/mol
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33
Aromatic Compounds
• Benzene, C6H6, in the
top 25 chemicals
produced in the U.S.
• Starting point for
hundreds of other
compounds.
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Resonance in Benzene
• C6H6 has two resonance structures with
alternating double bonds.
• The π electrons are delocalized over the ring.
H
C
HC
H
C
C
C
H
H
CH
H
H
C
C
H
C
C
H
CH
C
H
Resonance structures of benzene, C6 H6
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H
C
HC
H
C
C
C
H
H
CH
Abbreviated representation
of resonance structures
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Resonance in Benzene
• CC bond order is _______________
• C–C single bond = 154 pm
C=C bond = 134 pm
• CC bonds in benzene = 139 pm
π electrons delocalized
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Bonding in Benzene
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Other Aromatic Hydrocarbons
Toluene
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Naphthalene
Benzene Derivatives
38
Aniline
Phenol
C6H5NH2
TNT
trinitrotoluene
C6H5OH
C6H4CH3(NO2)3
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Naming Benzene Derivatives
Cl
1
6
2
3
5
4
39
Ortho to Cl
Meta to Cl
Para to Cl
1,4-dimethylbenzene
Common name: Para-xylene
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Reactions of Aromatics
• Substitutions — not additions — are
typical.
CH3
+ CH3Cl
AlCl3
AlCl3 is a catalyst. Catalysts typically used in
aromatic substitutions.
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+ HCl
41
Functional Groups
See CD-ROM Screens 11.5 & 11.6
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Alcohols
• Characterized by –OH group
• Name: add –ol to name of hydrocarbon
Methanol
Butanol
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Structures of Alcohols
C3H5OH: how many structural isomers?
H
H
H
H
C
C
C
H
H
H
1-propanol
OH
H
H
OH H
C
C
C
H
H
H
H
2-propanol
Naming: Add -ol to name of 3-C hydrocarbon. Indicate
position of OH with number.
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Alcohol Properties
• Alcohols are a derivative of water
• Many alcohols dissolve in water
Methanol dissolves
in water.
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Butanol is NOT soluble
in water.
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“Sterno”
• Alcohols burn in air
• A mixture of ethanol +
calcium acetate =
STERNO
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GLYCOLS
Alcohols with Two OH Groups
Ethylene
glycol
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Propylene
glycol
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Alcohol Reactions
Screen 11.6
Substitution
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Elimination—the
reverse of addition
48
TYPES OF ALCOHOLS
H
Primary
R
C
OH
CH3 CH2 OH, ethanol
H
CH3
R
Secondary
R
C
OH
R
R
C
R
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H3 C
C
H
H
Tertiary
rubbing alcohol
OH
OH
49
More Alcohol Reactions
H
H
C
H
C
OH ( )
+ Oxidizin g agent
H
H H
Eth anol
H
O
C
C
H ( )
H
Acetaldehyde
+ Oxidizin g agent
Ethanol is a PRIMARY
ALCOHOL. It is oxidized
to an ALDEHYDE and then
to an ACID.
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H
H
O
C
C
OH ( )
H
Acetic acid
50
More Alcohol Reactions
OH
R—C—R'
H
Secondary alcohol
oxidizing
agent
O
R—C—R'
Ketone
(–R and –R' are organic groups. They may be the
same or different.)
SECONDARY ALCOHOLS are oxidized to
KETONES — and reaction stops there.
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Sugars: Related to Alcohols
• Sugars are carbohydrates, compounds
with the formula Cx(H2O)y.
CHO
H OH
4
HO
HO
H
5
HO
3
H
H
2
HO
1
OH
OH
a-D-glucose
H
H
H
1
OH
2
H
3
OH
4
OH
5
CH2OH
H OH
4
HO
HO
5
HO
1
3
H
H
2
OH
H
b-D-glucose
Open chain form
What is the difference between a and b D-glucose?
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OH
52
Sucrose and Ribose
H OH
HO
HO
HO
HO
H
OH
O
H
H
CH2OH
H
HO
Fructose
H
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O
H
a-D-Glucose
OH
H
OH
H
H
H
Deoxyribose,
the
sugar
in
the
OH
H DNA
CH2 OH backbone.
O
Amines
53
Alcohols are derivatives of H2O (R–OH)
and amines are derivatives of NH3.
Methylamine
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Dimethylamine
Trimethylamine
Amines
54
Amines generally have terrible odors!
Cadaverine
Pyridine
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Amines
55
Amines, like NH3, are bases
2 C6H5NH2 (aq) + H2SO4(aq)
Aniline
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2 C6H5NH3 +(aq) + SO42-(aq)
Anilinium ion
Amines
56
Many natural
products and
drugs (such
as nicotine
and cocaine)
are bases.
H+
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Nicotine
57
O
C
Aldehyde
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Compounds with
Carbonyl Group
Carboxylic acid
Ketone
58
Structures of Aldehydes
Cinnamaldehyde
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Odors from aldehydes and
ketones
Carboxylic Acids
Acetic acid
Acids are found in
many natural
substances: bread,
fruits, milk, wine
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Benzoic acid
Carboxylic acid group
with acidic H+
All are WEAK acids
Carboxylic Acids
60
H
O
C
O
O
Formic acid,
HCO2H, gives
the sting to ants.
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C
CH3
O
Aspirin, acetylsalicylic acid
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Acids + Alcohols --> ESTERS
Esters have generally pleasant odors
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Acids + Alcohols --> ESTERS
O
O
CH 3COH + CH 3CH 2OH
Acetic acid
H+
CH 3COCH 2CH 3 + H 2O
Ethyl acetate
Ethanol
O
O
RC—O—H
+ R'—O—H
Carboxylic acid
Alcohol
H+
RC—O—R' + H 2O
Ester
One of the important reactions in nature!
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Acids + Alcohols --> ESTERS
3-methylbutanol
Acetic acid
O
H3C
C
CH3
O
CH2 CH2CHCH3
3-methylbutylacetate
Many fruits such as
bananas and strawberries
contain esters.
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Glycerol
Alcohol with 3 OH Groups
Combine this with long chain acids ------> ???
Fatty acids ---> fats and oils
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Fats and Oils
H2 C
HC
H2 C
O
O CR
O
O CR
O
O CR
What is the
functional group in a
fat or oil?
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R = organic group
with NO C=C bonds
C12 = Lauric acid
C16 = Palmitic acid
C18 = Stearic acid
R = organic group
with C=C bonds
C18 = oleic acid
H2 C
HC
H2 C
O
O CR
O
O CR
O
O CR
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Fats and Oils
Fats with C=C bonds are usually LIQUDS
Oleic acid: a
monounsaturated
fatty acid
C=C bond
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H2 C
HC
H2 C
O
O CR
O
O CR
O
O CR
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Fats and Oils
Fats with saturated acids (no C=C bonds)
are SOLIDS.
Saturated fats are
more common in
animals.
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Fats and Polar Bears
•Bears gorge on blubber
in the winter.
•During the summer
bears rely on stored fat
for energy.
•Burn 1-1.5 kg of fat per
day.
•Water for metabolism
comes from fat burning.
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Trans Fatty Acids
•Oleic acid is a mono–unsaturated cisfatty acid
•Trans fatty acids have deleterious health
effects.
•Trans fatty acids raise plasma LDL
cholesterol and lower HDL levels.
C=C bond
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Fats and Oils: Saponification
Glyceryl stearate, a fat + NaOH
O
CH2 O CR
O
+ 3 NaOH
CH O CR
O
CH2 O CR
R = —(CH2 )16CH3
CH2 OŃ H
CH OŃ H
CH2 OŃ H
Glycerol
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O
+ 3 RCŃ O- Na+
Sodium stearate, a soap
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Acids + Amines --> AMIDES
N-methylacetamide
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Acids + Amines --> AMIDES
H
C
H
H
H
O
H
O
C
C
C
C
C
C
N
H
H
C
H
H
Amide link
Acetoaminophen
Tylenol, Datril, Momentum, ...
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Alpha-Amino Acids
H2N
H
O
C
C
OH
R
Amine
H
Alanine
H3 C
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C
Chiral a-carbon
NH3
CO2
Acid
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Peptides and Proteins
O
HOCH2
H 3N
OŠ
H CH3
Alanine
+
H 3N
H
OŠ
O
Serine
peptide bond
– H2O
H
HOCH2
H
H 3N
O
N
H
O
OŠ
CH3
Adding more peptide links ---> PROTEIN
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Polymers
• Giant molecules made by joining many
small molecules called monomers
• Average production is 150 kg per person
annually in the U.S.
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Polymer Classifications
• Thermoplastics (polyethylene) soften and
flow when heated
• Thermosetting plastics — soft initially
but set to solid when heated. Cannot be
resoftened.
• Other classification: plastics, fibers,
elastomers, coatings, adhesives
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Polymer Preparation
• Addition polymers — directly
adding monomer units together
• Condensation polymers —
combining monomer units and
splitting out a small water (water)
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Polyethylene: Addition Polymer
n H2C
CH2
Ethylene
H
H
C
C
H
H n
Polyethylene
A polymer with a molar mass of
1e6 has about 360,000 units.
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Mechanism of Addition
Polymerization
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80
Types of Polyethylene
Linear, high density PE
(HDPE)
Branched, low density
PE, LDPE
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Cross-linked PE, CLPE
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Types of Polyethylene
Polymers based on Substituted Ethylenes, CH2=CHX
CH2CH
OH
CH2CH
n
polyvinyl alcohol
CH2CH
OCCH3 n
O
polyvinyl acetate
n
polystyrene
Table 11.12: others are PVC, acrylonitrile,
polypropylene, polymethyl methacrylate
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Polystyrene
• Polystyrene is nonpolar material and dissolves in
organic solvents.
• PS foam is mostly air, and when it dissolves it collapses
to a much smaller volume.
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Slime!
Slime is
polyvinylalcohol
cross-linked
with boric acid
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Bubble Gum!
A copolymer
Styrene + butadiene
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Condensation Polymers
O
n HOC
O
COH + n HOCH 2CH 2OH
terephthalic acid
O
C
ethylene glycol
O
COCH 2CH2O
+ H2 O
n
Polyethylene terephthalate (PET), a polyester
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Polyesters, PET
Jackets made from recycled
PET soda bottles
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Soda bottles, mylar
film.
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Polyesters: Mechanism
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Polyamides: Nylon
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Polyamides: Nylon
•Each monomer has 6 C atoms in its chain.
•A polyamide link forms on elmination of HCl
•Result = nylon 66
•Proteins are polyamides
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Polymer Recycling Symbols
LDPE =
HDPE =
PP =
V=
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Low density PE = 0.910-0.925 g/cm3
High density PE = 0.941-0.965
Polypropylene = 0.90
PVC (Vinyl chloride) = 1.30-1.58
90