CHEM219/ CHEM 219 Module 7 – Principles of
Organic Chemistry with Lab | Portage Learning |
Updated 2026–2027 | Complete Questions &
Verified Answers
...
| Grade A
2026 / 2027 Academic Year
Q: Heterocycles (heterocyclic compounds)
Answer
cyclic organic molecules in which one or more carbon atoms are replaced by heteroatoms
(elements other than carbon or hydrogen)
Q: What are the most common heteroatoms?
Answer
oxygen, nitrogen, and sulfur
Q: How many heteroatoms can be present on a heterocyclic compound?
Answer
More than one heteroatom can be present, and the heteroatoms can be the same or
different
Q: True or False: Heterocyclic compounds may contain multiple bonds and the rings may
have chains or branched chains of carbons attached to them. The rings may be of a variety
of sizes.
Answer
True
Q: True or False: Heterocycles form the largest class of organic compounds known.
Answer
True
Q: True or False: Many natural products and important drug molecules contain
heterocyclic rings.
Answer
True
Q: What are the two main subgroups of heterocyclic compounds?
Answer
Aromatic and aliphatic (non-aromatic)
Example of non-aromatic heterocycles include molecules like cyclic ethers (epoxides) and
sugars like glucose (a cyclic hemiacetal)
Non-aromatic heterocycles behave very similarly to their acyclic counterparts.
Q: Pyridine
Answer
A six-membered heterocyclic analog of benzene. In pyridine, one CH unit of the (benzene)
ring is replaced by a N atom.
Q: What are the bond angles between the atoms of pyridine?
Answer
Approximately 120 degrees
Q: True or False: Like benzene, pyridine is a flat molecule with near-perfect hexagonal
geometry?
Answer
True
Q: What hybridization are the atoms of the pyridine ring?
Answer
sp2
Q: What makes the pyridine ring aromatic just like benzene?
Answer
each atom is sp2 hybridized and each contributes a single electron to the conjugated p
system for a total of six p electrons, making the ring aromatic just like benzene
Q: True or False: The nitrogen atom of pyridine contains a lone pair of electrons in an sp2
hybrid orbital that is NOT orientated in the same plane of the atoms in the ring (like the
hydrogens that project from each carbon atom).
Answer
False - they are orientated in the same plane of the atoms in the ring.
Q: What are the C-C bond lengths in a pyridine molecule?
Answer
139 pm are intermediate between normal C-to-C sigma and pi bonds.
Q: True or False: Pyridine exists as a hybrid of equivalent resonance structures as
evidenced by the C-C bond length?
Answer
True
Q: What does the circle inscribed inside of the pyridine ring represent?
Answer
The delocalization of the pi electrons within the six-membered ring.
Q: What kind of reaction does pyridine tend to undergo and why?
Answer
Substitution reactions because addition reactions would destroy the aromaticity.
Q: True or False: Pyridine is completely miscible in water?
Answer
True; unlike benzene
This is due to the substitution of the N atom in the ring which changes many of the
properties of the molecules.
Pyridine is also miscible in most organic solvents.
Q: What are the several factors that explain the ability of pyridine to dissolve in water?
Answer
1. The ability of pyridine to accept hydrogen bonding interactions from water molecules due
to the lone pair of electrons on the N atom.
2. The electronegative N creates a relatively strong dipole moment in the pyridine molecule,
making it a polar compound overall. There is a shift of electrons away from the Cs and
towards the N, making the ring Cs partially positive and the N partially negative.
Q: What causes the difference in B.P. between pyridine and benzene?
Answer
B.P. of pyridine is 35 degrees higher than that of benzene, even though the molecular
weight is negligible between the two compounds. Dipole-Dipole attractive forces between
the pyridine molecules raises the B.P. as compared to benzene.
Q: Pyridinium salts
Answer
Pyridine is a weak base and will react with strong acids to form pyridinium salts. The ability
of pyridine to act as a base, coupled with its wide-ranging solubility, makes it suited to act
as a proton scavenger in acid-producing reactions, like the conversion of alcohols to alkyl
chlorides using thionyl chloride.
Q: EAS (Electrophilic aromatic substitution) reactions
Answer
Reactions in which a hydrogen is replaced by an electrophile (species that seeks
electrons/negative charge).
Q: Under what conditions will pyridine undergo EAS reactions?
Answer
Slowly and very harsh conditions
i.e. pyridine can be nitrated or brominated, as shown, but the reactions require very high
temperatures and very strong acid catalysis. Electron withdrawal by the N makes the ring
partially positive and, thus, not as receptive to attack by electrophiles like NO2+ or Br+. In
addition, the strongly acidic conditions required for the formation of these electrophiles
causes protonation of the N atom and the positive pyridinium ion formed as a result is even
less attractive to attack by electrophiles.
Q: When EAS does occur, what is the preferred position for the substitution on the ring?
Answer
C3 position
This position is preferred as the positive charge that forms on the C during the reaction is
the one position that does not put the positive charge on the electronegative N via
resonance.
Q: True or False: Pyridine can more easily undergo nucleophilic aromatic substitution
(NAS) than EAS?
Answer
True
In NAS, a nucleophile displaces a hydride (H-) ion or halide ion (on a substituted pyridine)
from the aromatic ring. Due to the presence of the N heteroatom, the ring is partially
positive and therefore is more attractive to nucleophiles, rather than electrophiles.
i.e. Strong nucleophiles like alkoxide ions (RO-) and amide ions (NH2-) help to facilitate
the reaction.
Azines
Answer
heterocyclic six-membered rings with two or more N atoms present as part of the ring
system
Diazines
Answer
contain two N atoms and can exist in three different constitutional isomeric forms;
pyrimidines are the most important because derivatives of pyrimidines are important bases
in the nucleic acids DNA and RNA namely cytosine, thymine, and uracil.
True or False: Tri- and tetrazines are also known, but no others with higher degrees of N
substitution (5 or 6 N atoms) are known.
Answer
True
What are the most important heterocyclic molecules with five-membered rings?
Answer
Furan (oxygen-based)
Pyrrole (nitrogen-based)
Thiophene (sulfur-based)
differences:
the heteroatom of a five-membered ring contributes two electrons (one lone pair) to the
These molecules each contain a carbon ring with a single heteroatom substitution.
What are some similarities and differences between five-membered rings and benzene (six
membered ring)?
Answer
Similarities:
aromatic
undergo EAS rather than other modes, like addition
planar (flat)
aromatic pi system of the ring to make the molecule aromatic while the six-membered
heterocycles have a heteroatom that contributes one electron to the aromatic pi system
What are some important consequences in terms of chemistry of the molecule for the use of
the lone pair of pyrrole in the aromatic pi system?
Pyrrole (five-membered) is a much weaker base than pyridine (six-membered) due to the
availability of the lone pair. In pyridine, the lone pair is available (not part of the aromatic
pi system) to accept an acidic proton. In pyrrole, this is not the case.
True or False: Protonation of the lone pair of pyrrole destroys the aromatic pi system and
the special stability of aromaticity; thus, pyrrole is much less likely to accept an acidic
proton on its N atom.
True
True or False: Furan and thiophene have two lone pairs on their respective heteroatoms.
While one lone pair is involved in the aromatic pi system, the other is in the same plane as
the atoms of the ring and is available for protonation.
True
"Pyrrole-like"
When the N atom of an aromatic heterocycle has single bonds only, then the lone pair
participates in the conjugated pi system to create aromaticity and is not available to react as
a weak base.
"Pyridine-like"
When the N atom of an aromatic heterocycle is participating in a pi bond, then the lone pair
occupies an sp2 orbital in the same plane as the ring and is available to react as a weak base.
True or False: Furan, pyrrole, and thiophene are all more reactive than benzene in EAS
reactions.
True
Each molecule reacts with electrophiles to substitute (for a hydrogen) at the C-2 position.
Why is substitution preferred at the C-2 position on five-membered heterocycles?
The carbocation intermediate that forms during the reaction is delocalized over more atoms
(and hence, more stable) when substitution occurs at this position.
Azoles
It is possible to introduce more than one heteroatom into a five-membered heterocycle. Of
the many available structural possibilities, the most important heterocycles are formed by
introducing a N atom in place of C-3 in furan, pyrrole, and thiophene. The resulting
molecules are known as azoles.
Thiazole
occurs naturally in thiamin (vitamin B1), a coenzyme required for many biochemical
processes essential to human life
The inclusion of the N at position C-3 results in a "pyridine-like" N, which is involved in a pi
bond.
Imidazole
A very good base, as the positive charge obtained from protonation of the N at position C-3
can be delocalized via resonance over both N atoms.
Imidazole is present in the amino acid histidine and is important in the reactions of many
enzymes.
Why do heterocycles form the largest class of organic compounds known?
Structural diversity in terms of their ring size and the number and identity of heteroatom
substitutions.
Another reason, is the possibility of fused ring systems.
Fused ring system
Two (or more) rings are fused together to form a larger molecule; to be fused means that
each ring shares two (or more) common atoms as a part of the structure of each ring.
Purines
Another biologically important class of fused-ring heterocyclic compounds. Purines contain
a pyrimidine ring fused to an imidazole ring.
Uric acid , caffeine, and theobromine (found in chocolate) are all based on the structure of
purine.
Biochemically, the structures of adenine and guanine, two of the nitrogenous bases present
in DNA and RNA are both purines.
Indole
a bicyclic, fused-ring compound formed by fusing a benzene ring to the C2-C3 bond of
pyrrole
Indole is a component in many biologically active compounds including the amino acid
tryptophan.
Heterocycles
cyclic organic molecule where one or more carbon atoms are replaced by heteroatoms
Heteroatoms
Atoms in an organic compound other than carbon and hydrogen
Ex: Oxygen, Nitrogen, Sulfur
Two main subgroups of heterocycles
1. aromatic
2. aliphatic (non-aromatic)
Pyridine
analogue of benzene where one C is replaced by N
geometry of pyridine
flat/ planar geometry with 120 degree bond angles
atomic structure of pyridine
sp2 hybridized atoms, 6 P electrons just like benzene
resonance structure of pyridine
Why does pyridine undergo substitution rather than addition?
addition would destroy the aromaticity
solubility of pyridine
soluble in most organic solvents and completely soluble in water
why is pyridine soluble in water? -ability of pyridine to accept hydrogen bonding interactions from water molecules d/t the
lone pair of electrons on the nitrogen. - electronegative N creates a relatively strong dipole moment in the pyridine, thus making it
an apolar compound overall.
BP of pyridine vs benzene? why? -pyridine has a higher BP than benzene even though they have a similar weight -why? dipole/dipole forces
Is pyridine an acid or base?
weak base
will form pyridinium salt when reacted with strong acids
Two main reaction types of pyridine?
1. EAS- Electrophilic Aromatic Substitution
2. NAS- Nucleophilic Aromatic Substitution
What happens in the EAS of pyridine?
a hydrogen is replaced by an electrophile
What conditions are needed for pyridine to undergo EAS?
very slow and very harsh conditions- need very hot heat and a strong acid
Why is pyridine less receptive to EAS than other molecules?
ring is partially positive d/t electron withdrawal by the nitrogen
What position does an EAS reaction prefer on a pyridine molecule?
C3 bc the charge wont put a positive charge on the electronegative nitrogen via resonance
Nucleophilic Aromatic Substitution
A substitution reaction in which an aromatic ring is attacked by a nucleophile, which
replaces a leaving group. -displaces a hydride ion or a halide ion from the ring
Why are NAS easier for pyridine than EAS?
the positive partial charge on the Nitrogen atom attracts nucleophiles
Azine
heterocyclic 6-membered rings with 2 or more nitrogen atoms as part of the ring system
Diazines
2 nitrogens replacing carbons in a benzene ring
3 isomeric forms of diazines
1. pyridazine N1, N2
2.pyrimidine N1, N3
3.pyrazine N1, N4
pyridazine
placement: 1, 2
pyrazine
placement 1, 4
Pyrimidine
placement: 1, 3 -most important, found in cyotosine and thymine (DNA/ RNA)
furan
oxygen-based 5-membered aromatic ring
pyrrole
nitrogen-based 5-membered aromatic ring
thiophene
sulfur-based 5-membered aromatic ring
5-membered heterocycles
furan, pyrrole, thiophene -aromatic/ behave like benzene -EAS reactions -Flat/planar geometry
Biggest difference between benzene and membered aromatic rings?
The heteroatom of a 5-membered ring contributes 2 electrons (1 lone pair) to the aromatic
system while the 6-membered heterocycles' heteroatom only contributes 1 electron to the
aromatic system
Pyridine or Pyrrole WEAKER base?
Pyrrole is a weaker base than pyridine bc pyrrole uses the lone pair from the nitrogen in the
aromatic stabilization system.
pronating the lone pair of pyrrole would destroy the aromaticity
Difference in Furan and Thiophene compared to pyrrole
Furan and thiophene have 2 lone pairs instead of one which leaves one lone pair for
protonations after the other is used in the aromatic pi system
Is pyridine or the 3 5-membered heterocycles more reactive in EAS reactions?
Furan, Thiophene, and pyrrole are more reactive in EAS reactions than pyridine
what atom number is preferred for EAS substitution on 5-membered heterocycles?
substitution at C2
carbocation intermediate that is formed during EAS is delocalized over more atoms and
thus more stable when at C2
Azole
more than one heteroatom in a 5-membered heterocycle
oxazole
oxygen at 1, nitrogen at 3
Imidazole
nitrogen at 1, nitrogen at 3
Thiazole
sulfur at 1, nitrogen at 3
What does the additional Nitrogen on azoles allow for?
lone pair on new nitrgoen means there is availability for the molecule to bond to an acidic
proton
Why is Imidazole a good base?
positive charge obtained from the protonation of nitrogen on position 3 can be localized via
resonance over both of the nitrogens
Imidazole is found in:
histidine (amino acid)
thiazole is found in:
Thiamine (B1 vitamin)
fused-ring system
a molecule in which two or more rings share two adjacent carbon atoms
indole
benzene + pyrrole
found in amino acid tryptophan
purine
pyrimidine ring fused to imidazole ring -found in uric acid, adenine and guanine (A & G in DNA)caffeine, theobromine (in
chocolate)
CHEM219/ CHEM 219 Module 8 – Principles of
Organic Chemistry with Lab | Portage Learning |
Updated 2026–2027 | Complete Questions &
Verified Answers
...
| Grade A
2026 / 2027 Academic Year
Q: Polymer
Answer
large molecule made by repetitive linking of smaller units (monomers)
Q: Macromolecule
Answer
very large molecule composed of thousands of covalently bonded atoms (ex: polymer)
Q: two ways polymers are made
Answer
1. natural (in nature)
2. synthetic (in lab)
Q: examples of natural polymers
Answer
rubber, carbs: starch & cellulose, proteins, nucleic acids DNA, RNA
Q: examples of synthetic polymers
Answer
nylon, teflon, styrofoam, polyethylene, Dacron,
Q: 3 main ways to differentiate polymers
Answer
1. method of formation
2. final composition
3. stereochemical orientation
Q: Two types of Synthetic polymers
Answer
1. chain-growth
2. step-growth
Q: chain growth polymers are also know as:
Answer
addition polymers
Q: How are chain growth polymers made?
Answer
made by addition of one monomer unit to another in a repetitive pattern
Q: chain growth polymerization
Answer
A polymerization involving sequential addition to monomers that are unsaturated (C=C) or
have some other reactive functional groups (particularly ethylene and derivatives)
Q: what 2 things stops chain growth polymerization?
Answer
1. intervention
2. consumption of all available monomers
Q: Teflon
Answer
chain-growth
polymer: polytetrafluoroethylene
monomer: F2C=CF2
nonstick coating, goretex, electrical insulator, chem-resistant coating
Q: Saran
Answer
chain-growth
polymer: polyvinylidenedichloride
monomer: H2C=CCl2
cling-wrap
Q: Polypropylene
Answer
chain-growth
polymer: polypropylene
monomer: H2C=CHCH3
carpet fibers, car parts, toys, packaging, houseware
Q: Orlon, Acrilan, Creslan
Answer
chain-growth
polymer: polyacrylonitrile
monomer: H2C=CH(CN)
textiles/fibers, carpets, upholstery
Q: Polyvinyl Acetate
Answer
chain-growth
polymer: polyvinyl acetate
monomer: H2C=CH(OCOCH3)
elmers glue, silly putty, latex paints
Q: Polyvinyl alcohol
Answer
chain-growth
polymer: polyvinyl alcohol
monomer: H2C=CH(OH)
eye med- artificial tears
Q: Plexiglass (Lucite)
Answer
chain-growth
polymer: polymethylmethacrylate
monomer: H2C=C9CH3)COOCH3
clear plastic sheets , blocks, and tubing
Q: the final polymer retains all of the atoms of the monomer
Answer
the final polymer retains all of the atoms of the monomer
Q: step growth polymerization
Answer
formed by the reaction between 2 different functional groups on different monomer
molecules with the accompanying loss of some small molecule (typically water)
Q: The defining characteristic of step-growth polymers
Answer
The final polymer chain does NOT include all the atoms initially present in the monomer
molecules
Q: step-growth polymers also known as:
Answer
condensation polymers
Q: functionality of step-growth monomers
Answer
typically di or polyfunctional
Q: appearance of monomers in step-growth polymerization
Answer
alternating order in the final polymer chain
Q: how step-growth polymers generally grow
Answer
by carbon-heteroatom bond formation
Q: how chain-growth polymers generally grow
Answer
carbon-carbon bond formation
Q: Polyamide (Nylon)
Answer
formed by combining 1,6-diaminohexane (amine) with 1,6-hexandioic acid (carboxylic acid)
amine functionality reacts with carboxylic acid functionality to form an amide with a
corresponding loss of a water molecule
naturally occurring step-growth/ condensation polymer examples
Answer
cellulose, polypetide chains, beta-Hydroxybutyric acid
Lexan
Answer
step-growth
polymer: polycarbonate
eye glasses, auto parts, drinking glasses
Kevlar
Answer
step-growth
polymer: polyamide
body armor, tires, helmets
step-growth
polymer: polyester
Dacron, Mylar
Answer
eletric/thermal insulation, helium balloons, artificial limbs
three main mechanisms for addition/ chain-growth polymerization
Answer
1. free radical
2. cationic
3. anionic
For all three main addition mechanisms, how does polymerization begin?
Answer
(initiation) begins by creating a reactive intermediate that starts the chain reaction
free-radical addition polymerization
Answer
a monomer reacts with a free-radical initiator to create a free-radical
free-radical
Answer
an atom or a group of atoms that has one unpaired electron
radical initiator
Answer
a reagent that creates radicals, has relatively weak covalent bonds which can be homolyzed
3 main characteristics of free-radicals
Answer
1. electrically neutral
2. quite reactive and reacts quickly to pair up the lone electron
3. formed from radical initiators
Homolyzed bond
Answer
broken so that each atom joined by the bond gets one of the two electrons in the bond
benzoyl peroxide
Answer
example of a radical initiator (o-o bond = weak and can undergo homolysis upon heat or UV
exposure to produce 2 benzoyl radicals)
how much initiator is needed in polymerization and does any remain at the end of the
reactions?
Answer
only a small amount of radical initiator is needed compared to the concentration of
monomers present -some remains in final product but it does not affect the product
two main things that control polymer properties
Answer
1. the monomer used
2. the molecular weight of the final polymer chain
what happens after the radical initiator has formed radicals?
Answer
radical can attack + homolyze C=C of monomer to create a reactive intermediate that starts
polymerization
which substituent does the radical add to in the monomer?
Answer
adds to the LEAST substituted carbon of the C=C bond because this carbon is easier to
approach and less hindered to produce a more stable radical intermediate
What happens during propagation of free-radical polymerization?
Answer
produces a new radical that can continue the polymerization chain reaction:
Each attack of the radical with a new monomer unit extends the chain by one unit
what is chain propagation the same as?
Answer
some step as initiation in that monomers add in head to tail fashion with substituents
present on alternating carbons in the chain
What 4 main factors determine the extent of the polymerization?
1. temperature
2. pressure
3. solvent used
4. monomer concentration
speed of free radical chain growth
Answer
extremely rapid- can grow by thousands of monomers in less than a second
Termination of free-radical polymerization
Answer
stops the chain growth, involves 2 radical species- pairing of 2 unpaired electrons and
formation of new covalent bond
2 pathways of termination
Answer
1. Radical Coupling
2. Radical Disproportionation
Radical Coupling
termination of free-radical polymerization where 2 radicals combine using the unpaired
electrons on each to make a new covalent bond
monomer arrangement in radical coupling
head-to-head arrangement, substituents are attached to adjacent carbons
radical disproportionation
One radical abstracts a hydrogen atom from another radical species which forms a new
covalent bond and makes and alkane- then an alkene is formed by the combination of
unpaired electrons on adjacent carbons
Radical Coupling AND radical disproportionation form what type of species from radical
species?
both form non-radical species from radical species which stops the growth of the polymer
chain
3 steps in a Chain Reaction of free-radical polymerization
1. Initiation
2. Propagation
3. Termination
Initiation of Free Radicals
production of a radical species from a non-radical species using heat or UV light
Propagation of Free Radicals
reaction of a radical with a non-radical producing a new radical species and continuing the
chain reaction
what is chain transfer dependent on?
Rates of the straight chain propagation steps versus the chain transfer steps -Rates are controlled by stability of the intermediate radicals that form as a product in each
Termination of Free Radicals
reaction of 2 radicals with each other producing a non-radical- no intermediate reactive =
reaction stops
chain transfer reaction
type of propagation step where a radical in one polymer chain abstracts a hydrogen atom
from a position in a different polymer chain which causes branching in a growing polymer
chain
Cation Chain-Growth Polymerization
best for substrates that can form stable carbocation intermediates (typically unsubstituted
substrates like bulky alkenes or alkenes with electron-donating substituents)
How is cation addition polymerization initiated?
By adding a strong acid to an alkene to form a carbocation intermediate
cation addition polymerization propagation
carbocation intermediate + new alkene monomer molecule adds one unit to the polymer
chain each time
cation addition polymerization termination
terminates by the removal of a hydrogen atom from a carbon atom adjacent to the
positively charged carbon to form an alkene (like in an elimination reaction)
main catalysts used for anionic addition polymerization
Grignard Reagents (R: -[MgBr]+)
Alkyllithium (R:-Li+)
Anionic addition polymerization
a form of chain-growth polymerization or addition polymerization that involves the
polymerization of monomers initiated with anions. The type of reaction has many
manifestations, but traditionally vinyl monomers are used.
Why use anionic addition polymerization
useful for alkenes with electron-withdrawing substituents such as cyano groups, phenyls,
esters
anionic addition polymerization propagation
chain grows by 1 anionic intermediate adding to the C=C bond of a monomer molecule.
monomer anion adds in place of a Grignard Reagent or Alkyllithium reagent.
each addition grows by one unit
anionic addition polymerization termination
accomplished by quenching reaction with a proton source such as water or alcohol
what is formed when a monosubstituted alkene monomer is polymerized?
a new chiral center is formed at every position where the substituent branches from the
back bone of the chain
Tacticity
describes the location in the polymer chain of chiral centers rather than using R or S
designation
3 main classes of polymer tacticity
1. Atactic
2. Isotactic
3.Syndiotactic
atactic
stereocenters have random configurations
Isotactic
all stereocenters have the same configuration
syndiotactic
Stereocenters alternate in configuration
atactic configuration is labeled as
Stereorandom
isotactic and syndiotactic are labeled as
Stereoregular
How does having different tacticity with the same monomer effect the monomer?
The same monomers with different tacticity will have different physical properties
EX: atactic polypropylene (soft matrix adhesive) vs isotactic polypropylene (high-melting
solid that can be molded or machined)
2 ways to control polymer stereochemistry
1. chain-end control
2. site control
preferential formation of chain-end control -1st chiral center that forms will determine all subsequent stereochemistry in the polymer -an existing chiral center will force an incoming group to one side of the molecule
Chain end control
at an existing stereocenter and the end of the chain, the next monomer will be influenced by
how the chiral center projects into space
Site Control
The specific shape of the reagent or catalyst that facilitates the reaction also determines the
stereochemistry.
Ziegler-Natta catalyst
most famous site control to prod stereoregular polymers. uses various transition metal
catalysts to control sites where monomers are added to the chain
Ligands
A molecule that binds specifically to a receptor site of another molecule. -coordinated to the metal ion that bind monomers prior to insertion into the growing chain -specifically utilized in Ziegler-Natta catalysts
what 2 factors of ligands orient monomers into position
shape and size hold monomers into position in ONE orientation
what two types of polymers can Ziegler-Natta catalysts be used on?
Isotactic and Syndiotactic (only stereoregular polymers)
Homopolymer
a polymer made up of one type of repeating unit. It is made from one monomer only.
Copolymer
polymers composed of more than one type of monomer -used to control properties of a polymer product (like flexibility or chemical resistance)
Random (Statistical) Copolymer
monomeric units distributed randomly and unevenly in the chain
Alternating Copolymer
monomeric units distributed regularly + alternating with nearly equimolar amounts in each
chain
Block Copolymer
long sequence/ blocks of one monomer is joined to a block of the second monomer
Graft Copolymer
side chains of a given monomer are attached to main chains of a second monomer
biggest causative agent of the exact sequence in copolymer chains:
relative reactivity of the monomers present
situation creates what copolymer?
A reacts rapidly with B but slow with self
B reacts rapidly with A but slow with self
alternating sequence (ABABABABABA)
two things that determine the reactivity of a monomer
1. number of substituents present
2. type of substituents present
situation creates what copolymer?
A and B are equally reactive towards each other and self
random sequence (ABBAAAAABABBBAABBBBBBBAABABBB)
situation creates what copolymer?
One monomer in in copolymer is more reactive than other to all species
mixture of two different homopolymers
situation creates what copolymer?
polymerization of monomer A is iniated, then B is added, then A is added, etc -particularly useful for anionic polymerization bc the living end (anion) stays active until
the reaction is quenched.
Block sequence
situation creates what copolymer?
first polymerize a monomer with additional functionality (a second double bond) in its
structure -makes a polymer with multiple bonds -homopolymer is formed -monomer B added with a radical initiator to graft section of B onto reactive sites of A.
Graft sequence
polymer properties are strongly affected by:
1. molecular weight (and distribution)
2. amount of branching (of the chain architecture)
how do long branches affect crystallinity?
undergo side-chain crystallization (able to form rows of crystals on their own)
how do short branches affect crystallinity?
Reduce crystallinity (interfere with the formation of crystals)
Amorphous polymers
polymer chains arranged in random manner- not regularly aligned as in a crystal
important example of an amorphous polymer
polystyrene (monomer styrene ((Vinyl Benzene)))
thermoplastic
softens upon heating and hardens upon cooling (property of polystyrene)
what is produced by adding a low boiling inert solvent like pentane to the polymerization
reaction of polystyrene where the pentane boils off into gas and the volatilization causes
bubbles that expand the polymer into a foam.
Styrofoam
What allows amorphous polymers to be made more rigid/ crystalline (and thus less
amorphous)
Cross-Linking
Cross-linking definition
small amounts of polyfunctional monomers are added to form links (covalent bonds
between growing chains)
these links tether the growing chains together in a less random, more crystalline order
characteristics of cross-linked polystyrene
more rigid, less soluble in organic solvents than native
what are the main properties that characterization techniques of polymers seek to discover?
molecular mass, molecular structure, morphology, thermal properties, mechanical
properties
molecular mass of polymers
differs from typical molecules d/t polymerization reaction producing a distribution of
molecular weights and shapes
molecular mass of polymers =
average molecular weight and polydispersity
Polydisperity (PD)
how heterogenous the range of particle size is
Spectroscopy: UV-visible, infrared, Ramen, Nuclear magnetic resonance, electron spin
resonance, xray diffraction, mass spectrometry
techniques used to characterize polymers by identifying common function groups + other
structure features
(also used to determine molecular structure of unknown molecules)
an atom has gained or lost electrons
ion
a characteristic of atom that varies regularly across the periodic table
periodic property
a compound held together by a shared pair of valence electrons
covalent compound
a compound formed by ions
ionic compound
the electrons that exist farthest from the atom's nucleus and generally have the highest
energy level number
valence electrons
most atoms strive to attain eight valence electrons
octet rule
an indicator of an atom's size
atomic radius
the amount of energy needed in order to take an electron away from an atom
ionization potential
a measure of how strongly an atom attracts extra electros to itself a
electronegativity
the process by which an atom turns into an ion by gaining or losing electrons
ionization
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