Download - 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

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

Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.


Learning objective:

Describe functional groups and linkage groups in 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.


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


Examples of Alcohols and a Thiol


Ammonia and Amines


The Carbonyl and Carboxyl Groups


Important Polymer Linkage Groups


…and phosphate linkages


Learning objective:

Describe polymers made by 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.


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.



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.


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.


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.



Learning objective:

Describe polymers made by condensation polymerization



Condensation reaction: the formation of a bond between two molecules eliminating water or some small molecule.


Polyamides

Amide – a condensation of an amine and a carboxylic

Polyamides – polymers that contain amide linkage groups



Polyamides


Polyesters

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


Polyesters

Comprise largest segment of market of synthetic fibers (40%)

Poly(ethylene terephthalate) is the leading polymer



Learning objective:

Recognize and describe some properties of plastics, fibres, and elastomers



Polymers can be divided into three categories based on their form and resistance to stretching: Plastics Fibers Elastomers


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


Plasticizers

Improve the flexibilities of some plastics


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.


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.


Effects of Cross-Linking on Rubber



Recycling Polymers

18.5 Carbohydrates

Learning objective:

Recognize and draw structures of monosaccharides and polysaccharides


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


• 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


Example 18 – 3 Monosaccharide Structures

Describe the differences in structures of ribose and fructose


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.


Disaccharides

Formed by the condensation reaction of two monosaccharides.


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.


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


Polysaccharides

Cellulose and Starch – both are made from glucose monomers


18.6 Nucleic Acids

Learning objective:

Draw primary and secondary structures of DNA and RNA


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)


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)


2. A pentose sugar• RNA - ribose• DNA – deoxyribose

3. A phosphate linkage derived from phosphoric acid


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


Example 18-6 Drawing Nucleotides

Draw the structure of uridine monophosphate (UMP).


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


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


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


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?


(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.


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.


The structure of an RNAmolecule. Notice the folding caused by theintrastrand base paring.


18.7 Proteins

Learning objective:

Explain primary, secondary, and tertiary structures of proteins


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.


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


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.


• 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


By convention, the terminal amino acid group is written on the left and the terminal carboxylic acid group is written on the right.


Example 18 – 7 The Primary Structure of a Peptide

Draw the line structure of the peptide Asp-Met-Val-Tyr.


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.


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


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


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


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.


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.


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


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.



Chapter 18 Visual Summary

Download - 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

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