18.1 Starting Materials for Polymers
18.2 Free Radical Polymerization
18.3 Condensation Polymerization
18.4 Types of Polymers
18.5 Carbohydrates
18.6 Nucleic Acids
18.7 Proteins
Chapter 18. Macromolecules
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18.1 Starting Materials for Polymers
Learning objective:
Describe functional groups and linkage groups in polymers
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18.1 Starting Materials for Polymers
What is a polymer? A polymer is a macromolecule constructed by linking together
many copies of much smaller molecules called monomers. Monomers are organic molecules characterized by their
functional groups. Functional groups – specialized groups of atoms that impart a
specific chemical function.
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Polymerizable Functional Groups
Functional groups are only a part of an organic molecule.
R – represents the less important part of the molecule, and can be H or an organic fragment containing carbon atoms
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Examples of Alcohols and a Thiol
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The Carbonyl and Carboxyl Groups
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Important Polymer Linkage Groups
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…and phosphate linkages
18.2 Free Radical Polymerization
Learning objective:
Describe polymers made by free radical polymerization
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18.2 Free Radical Polymerization
e.g. the synthesis of polyethylene is a three-step sequence
Initiation – a reactive chemical attacks the bond of a single ethylene molecule.
Propagation – the product from step 1 reacts readily with the bond of another ethylene molecule. Several of these steps occur, building a long chain.
Termination – chain growth comes to an end when two long chains join.
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Initiation – an initiator molecule is added to ethylene, with heating, a free radical is formed and the first step occurs
Propagation – the first step leaves a carbon atom with a free radical, ready for another addition of ethylene
Termination – the process ends when two radicals collide and react.
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Important Polymers made from Alkenes
Example 18 – 1 Drawing the Structure of a Polymer
Polyacrylonitrile, known commercially as Orlon, is made by polymerizing acrylonitrile (see Figure 18 – 3). Orlon is used to make fibers for carpeting and clothing. Draw the Lewis structure of polyacrylonitrile, showing at least three repeat units.
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Rubber
Polyisoprene – the first alkene polymer to be used in society, came from sap of rubber trees.
Now, several forms of rubber are commercially produced by polymerizing mixtures of two different monomers to give copolymers.
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Cross-linking
How are rubbers made durable and strong if polymers are long chain molecules? Wouldn’t they only be held together by weak intermolecular forces?
They are chemically treated to create covalent bonds between the long chain molecules.
This process is referred to as cross-linking.
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18.3 Condensation Polymerization
Learning objective:
Describe polymers made by condensation polymerization
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18.3 Condensation Polymerization
Condensation reaction: the formation of a bond between two molecules eliminating water or some small molecule.
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Polyamides
Amide – a condensation of an amine and a carboxylic
Polyamides – polymers that contain amide linkage groups
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Example 18 – 2 The Structure of a Polyamide
Qiana, a polyamide that feels much like silk, has the following structure:
Identify the monomers used to make Qiana
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Polyesters
Comprise largest segment of market of synthetic fibers (40%)
Poly(ethylene terephthalate) is the leading polymer
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18.4 Types of Polymers
Learning objective:
Recognize and describe some properties of plastics, fibres, and elastomers
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18.4 Types of Polymers
Polymers can be divided into three categories based on their form and resistance to stretching: Plastics Fibers Elastomers
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Plastics
Plastic is a type of polymer that hardens on cooling or evaporation of the solvent. Thermoplastics – plastics that melt or deform when heated
High Density Polyethylene (HDPE) – very rigid and strong, used to make bottle caps, toys, cabinets for electronic devices
Low Density Polyethylene (LDPE) – soft, semi-rigid, used to make plastic bags, squeeze bottles
Thermosetting – plastics that retain their structural integrity when heated Formica
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Plasticizers
Improve the flexibilities of some plastics
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Fibres
Synthetic fibres are thin threads of polymer made by forcing a fluid thermoplastic material through a set of tiny pores.
The polar functional groups produce strong dipolar forces that add significant strength to the material.
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Elastomers
A flexible polymer that can be distorted.Most contain alkenes (double bonds)The polymer chains are held together by cross-links.The number of cross-links will determine the degree of flexibility and the
strength of the polymer.
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Effects of Cross-Linking on Rubber
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18.5 Carbohydrates
Learning objective:
Recognize and draw structures of monosaccharides and polysaccharides
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18.5 Carbohydrates
Carbohydrates are monomers and macromolecules with empirical formulas of Cx(H2O)y where x and y are integers.
Important food source for most organismsMonosaccharides: small molecules that when broken down
provide quick energy for cells (sugar high) Glucose, sucrose, fructose
Polysaccharides – macromolecular carbohydrates that store large amounts of energy Glycogen, cellulose, chitin
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• Have a formula of (CH2O)n where n is 3, 4, 5, or 6.• The most important ones contain 5 carbons or 6 carbons in
a ring.• Monosaccharides are cyclic compounds with an oxygen
atom forming an ether linkage in one of the ring positions. • The carbons are numbered for identification purposes.
Monosaccharides
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Example 18 – 3 Monosaccharide Structures
Describe the differences in structures of ribose and fructose
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Example 18 – 4 Drawing Monosaccharides
The six-carbon sugar -galactose is identical to a-glucose except at carbon atom number 4, where the orientations are different. Draw the molecular structure of -galactose. Simplify the structure using flat rings rather than the true three-dimensional forms.
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Disaccharides
Formed by the condensation reaction of two monosaccharides.
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Example 18 – 5 Decomposing a Sugar
Whereas humans can obtain energy from sucrose, insects obtain energy from trehalose, whose line structure follows. Identify the monosaccharides from which trehalose is constructed.
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Polysaccharides
Macromolecules made up of linked monosaccharides have two main functions: To act as structural materials (cellular make up) To act as reservoirs for energy
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Polysaccharides
Cellulose and Starch – both are made from glucose monomers
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18.6 Nucleic Acids
Learning objective:
Draw primary and secondary structures of DNA and RNA
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18.6 Nucleic Acids
The instructions for self-replication in biological organisms is stored and transmitted by macromolecules called nucleic acids
Genetic information is stored in molecules of DNA (deoxyribonucleic acid) located in the cell nuclei. (M > 109 g/mol)
The information stored in DNA is transmitted by RNA (ribonucleic acid). (M = 20,000 – 40, 000 g/mol)
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Building Blocks of Nucleic Acids
1. A nitrogen containing organic base• Purines: two-ring structures, adenine and guanine• Pyrimidines: one-ring structures, thymine (only in DNA),
cytosine (in DNA and RNA) and uracil (only in RNA)
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2. A pentose sugar• RNA - ribose• DNA – deoxyribose
3. A phosphate linkage derived from phosphoric acid
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Building Blocks of Nucleic Acids
The formation of adenosine monophosphate (AMP) by condensation of adenosine and phosphoric acid. The three linked units form the nucleotide building block required for nucleic acid synthesis.
2 13
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Example 18-6 Drawing Nucleotides
Draw the structure of uridine monophosphate (UMP).
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Structure of Nucleic Acids
A nucleic acid polymer contains nucleotide chains in which the phosphate group of one nucleotide links to the sugar ring of a second. The primary structure: the sequence of bases
ACGT in this example
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Secondary Structure of DNA
Elucidated by Watson and Crick in 1953 with data taken by Rosalind Franklin. (Died before the Nobel was awarded)
DNA consists of two strands of sugar-phosphate backbones wound one around the other in a double helix.
The two helices are connected by hydrogen bonds between bases that pair within the molecule.
Complimentary base pairs – the matching of bases Adenine pairs with thymine Guanine pairs with cytosine
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N
N
N
N
O
N H
H
H
N
N
O
O
H
N N
NN
NHH
H
N
N
O
NHH
H
Is this going to happen?
A
C
G
T
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N
N
N
N
O
N H
H
H
N
N
O
NHH
H
N N
NN
NHH
H
N
N
O
O
H
Hydrogen bonding!
A T
GC
Or this?
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
(a) A ball-and –stickmodel, with the sugar-phosphate backbone colored blue and the bases colored red. (b) Aspace-filling model,showing C atoms inblue, N atoms in darkblue, H atoms in white, O atoms in red, and P atoms inyellow.
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Structure of DNA
Structure of RNA
Similar to DNA, but… Sugar is ribose (not deoxyribose) RNA uses uracil instead of thymine RNA is much smaller RNA is usually single-stranded, not double-stranded.
Complimentary base pairing (G-C and A-U) creates loops and kinks
The principle job of RNA is to provide information to synthesize proteins.
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The structure of an RNAmolecule. Notice the folding caused by theintrastrand base paring.
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18.7 Proteins
Learning objective:
Explain primary, secondary, and tertiary structures of proteins
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18.7 Proteins
The most important biochemicals in cells are proteins (enzymes, antibodies, hormones, transport molecules, and structural materials) Protect organisms from disease Extract energy from food Move essential cellular components Responsible for vision, taste and smell And many other tasks
Proteins are the molecular machinery of the cell.
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All proteins are polyamides.
Amino acids make up proteins.
All amino acids in proteins have a central carbon bonded to one hydrogen and to a side chain group, R
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Of the 20 amino acids, 11 have side chains containing polar groups (in yellow), and 9 have nonpolar side chains. One, proline, has a unique ring structure.
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• Amino acids condense to create an amide linkage.• The amide group that contains the two amino acids is called a
peptide linkage.• Protein synthesis occurs by sequential condensation at the
carboxylic end of the growing chain leading to a polypeptide.
Polypeptides
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By convention, the terminal amino acid group is written on the left and the terminal carboxylic acid group is written on the right.
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Example 18 – 7 The Primary Structure of a Peptide
Draw the line structure of the peptide Asp-Met-Val-Tyr.
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Primary Structure of a Polypeptide
The sequence of amino acids is called the primary structure.
They are represented using short-hand notations for the amino acids.
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Secondary Structure
Certain sections of a long polypeptide will fold into sheets or twist into coils. The Helix Pleated Sheets
These regions constitute the secondary structure.The 2° structure is determined by hydrogen bonding
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A helical secondary structure results from hydrogen bonding within a single protein. The side chains are omitted to emphasize the shape of the helix. Notice the hydrogen bonding between N-H and C=O groups.
2° Structure: The Helix
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The pleated sheet: the chains in a sheet are fully extended rather than coiled, and hydrogen bonds exist between different portions of the protein chains. The pleats are caused by the bond angles of the peptide linkages.
2° Structure: The Pleated Sheet
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Tertiary Structure
Each protein has a unique 3D shape called the tertiary (3o) structure
This results from the bends and folds the peptide chain makes to achieve the lowest possible energy.
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Example 18 – 8 Hydrogen Bonding in Proteins
Draw a line structure that shows the various ways in which water molecules form hydrogen bonds with a protein backbone.
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Globular Proteins
Carry most of the work done by cellsAre compact, roughly spherical structures with folds
and grooves Enzymes: globular proteins that speed up biochemical
reactions Hemoglobin, antibodies, and hormones
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Fibrous Proteins
Structural components of cells and tissue are made of proteins that form fibres.
The fibrous proteins are the cables, girders, bricks and mortar of organisms.
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