Organic Chemistry
History:
Vital Force Theory: organic molecules can only be created by living organisms.
In 1828, Professor Wöhler was finishing up his post-doctoral work as a student. While working the laboratory he
succeeded in synthesizing an organic compound, urea, previously observed only in living tissue. Wöhler, pictured
below, made this organic compound from a non-living chemical substance, Ammonium Cyanate. He evaporated a
solution of Ammonium Cyanate to produce Urea. Organic Chemistry has undergone a substantial change since
then. There are well over a million synthetic organic compounds. Organic Chemistry is defined as the Chemistry of
Carbon and its compounds.
Carbon is a Lego like element. These atoms tend to form bonds with themselves creating different shapes. Like
the two below, octane on the left and a steroid precursor on the right.
The shapes are created by the chemical property of carbon to form 4 bonds.
Hybridization:
The 4 bonds carbon forms is explained by Linus Pauling’s theory of hybridization. Carbon atoms have an electron
configuration of 1s2 2s2 2p2 This configuration corresponds to the following energy level diagram.
2p
2s
1s
From the looks of this diagram, carbon might form 3 bonds as appears to be nowhere for a 4th bond to form. Linus
theorized that the two sublevels, s and p, in the second energy level formed a hybrid sublevel.
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This new energy level diagram is draw below
2sp
1s
This shows four open orbitals, allowing for the formation of four bonds. Linus won a noble prize for this theory.
Depending upon the number and types of bonds will dictate the hybridization of a carbon atom. A carbon atom
with four single bonds is designated as sp3, with two single bonds and one double bond sp2 and with one single
and one triple or with two double bonds is designated as sp.
When carbon atoms are bonded using all single bonds, sp 3, a molecular shape is formed (draw the Lewis structure
for CH4 to confirm this to yourself). In this instance the carbon atom forms bonds with 4 other atoms, resulting in a
tetrahedral shape, the blue sections of the below picture. This shape is formed by the repulsion of the electrons
which surround all atoms. So, if four objects are connected to a central object the farthest these objects can be from
each other forms a tetrahedral shape. The angle between these bonds is 109.5.
When carbon atoms are bonded using one double bond and two single bonds, sp 2, a molecular shape is formed
(draw the Lewis structure for H2CO (H only bonds to C) . In this instance the carbon atom forms bonds with 3
objects, resulting in a triangular shape (the blue sections of the below picture). This shape is formed by the
repulsion of the electrons which surround all atoms. The angles between these bonds are 120. The clear bubbles
are showing a pi-bond, a hybrid p orbital which will be used to create the double bond.
When carbon atoms are bonded using one single bond and one triple bond or two double bonds, sp, a molecular
shape is formed (draw the Lewis structure for CO2 or HCCH (as written) to confirm this to yourself) . In this
instance the carbon atom forms bonds with 2 objects, resulting in a linear shape, the blue sections of the below
picture. This shape is formed by the repulsion of the electrons which surround all atoms. So, if two objects are
connected to a central object the farthest these objects can be from each other forms a linear shape. The angle across
2
this bond is 180. The clear bubbles are showing pi bonds, hybrid p orbitals which will be used to create the double
or triple bonds.
The shapes around a given carbon atom will have the following shapes based on their hybridization, sp 3, sp2, sp
respectively.
General Properties of Organic Molecules:
1. Flammable
2. High Vapor Pressure
3. Odorous
4. Covalently Bonded
5. Non-Polar – functional groups can change these from non-polar to polar or cause the molecule to be bi-polar.
6. Low Solubility in Water – due to being non-polar as water is polar
7. Rate of Chemical Reaction is Normally Slow
8. Normally Found as Gases and Liquids at Room Temp
9. Non-Conductive of Electrical Current
Alkanes:
The first classification for organic molecules is the most simple, the alkane. The most simple alkane consists of only
carbon and hydrogen atoms connected by single bonds.
Alkanes are common and for the most part chemically unreactive, the chemical reaction combustion being the
major exception.
Alkanes can be found in many common substances; natural gas, gasoline, plastics…
The chemical formula can be generalized as:
CnH2n+2
Where n represents the number of carbons and 2n+2 equals the number of hydrogen’s.
Nomenclature:
Nomenclature is the scientific term for naming compounds. The governing body is “The International Union of
Pure and Applied Chemistry”, or IUPAC for short. The following statement is from their web site:
“The International Union of Pure and Applied Chemistry (IUPAC) serves to advance the worldwide aspects of the
chemical sciences and to contribute to the application of chemistry in the service of Mankind. As a scientific,
international, non-governmental and objective body, IUPAC can address many global issues involving the
chemical sciences.”
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IUPAC was formed in 1919 by chemists from industry and academia. One of there main functions is to objectively
create rules for naming compounds in the most simplified manner possible. This is equivalent to creating a new
language, just like English grammar, there are rules.
Even with the advent and acceptance of the IUPAC system some common names still persist, when discussing a
substance the IUPAC name should be used but the common name will be accepted by most chemical
organizations.
Alkane Nomenclature:
Naming of organic structures, unlike biological classification, follows a rigid set of rules. The International Union of
Pure and Applied Chemistry, abbreviated IUPAC, came up with a set of rules that follows the same standards
worldwide, and is accepted among all chemists. However, common names of compounds, or names that have
historical roots, are still used today for many compounds.
The suffix for the alkane family is –ane.
prefix – root – suffix
prefix – where the substitutions, or other interesting things (anything but hydrogen is
interesting to organic chemists!) is/are located. The number associated with the interesting
“thing” or side group will always receive the lowest number possible in the alkane chain.
root – how many carbons are in the longest chain in the molecule (the longest chain might twist
and turn. Longest chain represents carbon atoms that are bonded to each other.
suffix – family – type of functional group (alkane, alkene, alcohol, ester, etc...)
Root words are named for its number of carbons:
# of carbons
root
1
meth2
eth3
prop4
but5
pent6
hex7
hept8
oct9
non10
decExample:
an alkane with 3 carbons is named propane
prop – for the 3 carbons
ane – for the family alkane (meaning all single bonds)
Formula Types:
A variety of methods are used to describe a chemical compounds composition. Sometimes you will find the
chemical formula sufficient. Other times you need to see the structure drawn out, this is referred to as the
structural formula. This is a larger drawing which will show the atoms are connected. Another is the condensed
structural formula, this shows the connections in around about manner. Lastly, a more lazy form is the line
structure. This simplified drawing assumes you know that carbon atoms make 4 bonds and that if you do not see a
4
bond drawn assume a hydrogen is occupying the undesignated bond. Also all ends and turns in the line signify
carbon atoms.
Examples:
Chemical Formula:
C4H10
Condensed Structural Formula:
CH3CH2CH2CH3
Structural Formula:
Line Structure:
H H H H
H C C C C H
H H H H
Rules:
1.
2.
3.
4.
5.
Find the longest chain of carbons, and use this number as the base/root/parent name
Number the chain with the end nearest the first substituent carbon #1.
Give the location of the alkyl substituent by the number of the main-chain carbon that it is attached to.
Put the Substituents in alphabetical order (i.e. ethyl before methyl)
Substitution Syntax:
a. between numbers and words add a dash
b. between numbers add commas
Examples:
4-ethyl-octane
Correct
5-ethyl-octane
Incorrect
4-ethyl-2-methylheptane
Correct
4-ethyl-6-methylheptane
Incorrect
2-methyl-4-ethylheptane
Incorrect
Isomers:
Structural Isomers – have the same molecular formula, but different structure (are connected/bonded differently).
This is important as it causes different chemical and/or physical properties for the molecule. The number of
possible isomers increases rapidly as the length of the chain increases. These molecules are isomers of the same
chemical formula.
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Examples:
Each of the following molecules has a chemical formula of C4H10 but they are different molecules having different
properties.
butane
2-methyl propane (isobutane)
More Examples:
hexane
2-methyl pentane
3-methyl pentane
2,3-dimethyl butane
2,2-dimethyl butane (not 3,3-dimethyl butane)
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Cyclic Alkanes:
Alkanes can form compounds with themselves. By this I mean they commonly form rings.
Shown below is cyclohexane. It is a hexane molecule that has come around back onto itself. The below you will
find the chemical formula, structural formula and the line diagram.
H
C6H12
H
H
C
H
C H
H C
H C
C H
C
H
H HH
Sources of Alkanes:
Crude oil is the main supplier. Crude oil is gently heated in a tower, this heating produces vapors, the lighter
compounds to rise higher in the tower, while the heavier compounds rise very little. Collection equipment is
stationed at various levels ready to remove hydrocarbons of various masses. Alkanes tend to be light and very
non-polar, thus they travel to the top of the tower. Natural gas is the name given to the lightest of the alkanes, this
gas is a combination of methane, ethane and propane. Natural gas pockets are found above large deposits of crude
oil. (see picture of refinement tower below).
Alkanes can also be made these synthetically in a lab, like Professor Wöhler, in 1828 made urea. But his process is
time consuming and expensive. Verify this yourself by pricing synthetic motor oil verse regular motor oil.
Synthetic can easily be 15 times more expensive
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Modifications of Straight Chained Alkanes: Cracking
Hydrocarbons are indeed flammable, but as it turns out this is not enough to make a fuel a “good” fuel. An
important characteristic for fuels made up of different chemicals, like the mixture named gasoline, is that all the
fuels ignite at the same time. If some fuel ignites before it is designed to ignite undesirable result occur. This
phenomenon in your conventional internal combustion engine is called “Engine Knock.” The effects of engine
knocking vary, some symptoms include; unpleasant sounds, poor fuel economy, poor engine performance or even
engine damage.
The timing of ignition is very important. Many processes are occurring in concert with each other to deliver
smooth power to the cars wheels. Pistons are rising then being forced down by the explosion of these hydrocarbon
vapors mixed with oxygen gas from the atmosphere. The idea is to detonate this mixture, with a spark plug in
gasoline engines, when the piston has reached the top of the chamber, as the fuel explodes the piston is forced
down, this downward motion is mechanically converted to rotating motion and transferred to the wheels.
The knock occurs when some of the fuel enters the cylinder and ignites before the spark plug has fired. This causes
the piston to apply force to the parts in the motor at that are not designed to accept this force, at this time. The
reason for the premature ignition is due to the varied flammability of the different hydrocarbons found in gasoline.
Some hydrocarbons fire simply because they find themselves in a hot cylinder, and ignite before the spark plug
sparks.
You have no doubt seen the different ‘flavors’ of gasoline available at any gas station. Normally “octane numbers”
87, 89 and 92 are available. The higher the number the less chance of knocking. The alkane heptanes is considered
the worst and is assigned an octane number of 0. 2,2,4-trimethylpentane, common name isooctane, earns an octane
number of 100.
2,2,4-trimethylpentane
So, the more isooctane the higher the octane number and the less likely you will have a knock occur. The more
branching the better the fuel. Catalytic cracking, breaks apart straight chained alkanes, then catalytic reforming
“reforms” the bonds, as branched hydrocarbons. The above isooctane could have been octane cracked and
reformed as isooctane. The branching gives the molecule increase stability. Is allows it to withstand higher
temperatures as it waits to be ignited by the firing spark plug. Aromatics, compound containing benzene rings, are
also desirable hydrocarbons due to their high stability.
Alkenes: the presence of a double bond.
Alkenes are very similar to alkanes. In fact, all organic functional groups that we will be dealing with will be based
off the alkane (simple carbon) structure. An organic molecule is determined to be an alkene if there are carbons
that are doubly bonded to one another. The naming system is VERY similar to the alkane – so be careful.
prefix – root – ene
You will need to find the longest carbon chain that CONTAINS the double bond functional group. You will then
number your carbon chain beginning at the end nearer to the double bond. IF the double bond is equidistant from
either end, check to see if other functional groups or branch points are present. Make sure that the numbers
assigned to those other branch points are as low as possible. Multiple double bonds are indicated by additional
prefixes such as dienes, trienes, etc. (di for a species that contains 2 double bonds, and tri for a species that contains
3 double bonds).
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Consider the following structure below:
CH3CH=CHCH3
compared to
CH2=CHCH2CH3
Both compounds contain 4 carbons and 8 hydrogens. What is different about them? Right! The location of the
double bond. So this is something that the name of the compound will help us in differentiating between the two
compounds. These two species are not the same, they will not behave the same chemically and therefore they will
not and can not have the same name
Concept Test:
CH3CH=CHCH3
compared to
CH2=CHCH2CH3
What is the root for a species that has 4 carbon?
Since there is a double bond present, what will the suffix be?
Number the carbons on the structure on the left. What carbon does the
double bond begin on?
Number the carbons on the structure on the right. What carbon does the
double bond begin on?
Therefore the name of the species on the left is
The name of the species on the right is
These species have the same molecular formula. But they are different. We had a name for chemical species like
this – what was it? Right – an isomer.
When more than one double bond is present in a compound the location of EACH double bond must be identified
by a number (the lowest numbering system is still used!) and then since more than one double bond is present, the
name will be a diene or a triene, etc.
Concept Test
Name the following:
CH3CH=CHCH=CHCH2CH2CH3
CH2=CHCH2CH2CH=C=CH2
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Alkynes: presence of a triple bond
Again the naming system will follow the base alkane naming system. You will need to find the longest carbon
chain that contains the triple bond moiety. The carbons will be numbered at the end nearest to the triple bond.
Multiple triple bonds are named as diynes or triynes.
Example: HCCCH2CH2CH3 is named as 1-pentyne
Organic Functional Groups:
Organic molecules can be very complex, not only for their ability to branch off but also for specialized groupings of
atoms each of which give molecules special properties. Most any of these groupings, named organic functional
groups, can attach themselves to any organic molecule in most any location. One molecule may have more than
one of these groups giving the molecule different properties. In our studies of “Organic Chemistry” the reactivity
of these functional groups will a main focus.
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Alcohols, and Phenols
This set of notes discusses another set of related organic functional groups. The groups can be found attached to
normal straight chain alkanes as well as unsaturated organics: alkenes, alkynes and aromatics. Alcohols and
phenols deal with oxygen groups
Here are the general formulas and examples of each.
alcohol
general
structure
phenol
OH
R OH
H H
example
structure
OH
H C C OH
H H
example
name
Br
ethanol
or
ethyl alcohol
o-bromo phenol
or
2-bromo phenol
Nomenclature of Alcohols:
1. Select the longest chain containing the alcohol, -OH.
2. Number the chain with the –OH group getting the lowest possible number.
3. Replace the –e at the end of the suffix with –ol.
4. If there are more than one –OH group do not remove the –e from the suffix, but add a di- or tri- prefix to the –
ol suffix.
5. Add a prefix number to indicate which carbon the –OH group is bonded to. This is not always necessary.
Examples:
ethanol
H H
H C C OH
H H


2-propanol
or
isopropyl alcohol
(rubbing alcohol)
2,4-pentanediol
cyclopentanol
H OH H
H C C C H
OH
OH
H H H
OH
For the first example there is no prefix number to indicate the location of the –OH group. The reason is that no
matter which carbon the –OH group is attached to that carbon is carbon number one. The name 1-ethanol
would be redundant.
For the last example there is no prefix number to indicate the location of the –OH group. The reason is that no
matter which carbon the –OH group is attached to that carbon is carbon number one. The name 1cyclopentanol would be redundant.
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Alcohols are often classified based on the classification of the carbon they are attached to.

primary carbon is bonded to one other carbon:
o both of these carbons
H H
H C C
H
H H

secondary carbon is bonded to two other carbons:
o the center red carbon only
H H H
H C C C H
H H H

tertiary carbon is bonded to three other carbons:
o the center red carbon only
H
H C
H
H
H
H C
C C
H
H H H
Following the format of the above diagrams, if we replace one hydrogen with a –OH group we get the following
classifications of alcohols:

1, primary alcohol has –OH group bonded to a carbon which is bonded to one other carbon:
H H
H C C
OH
H H

2, secondary alcohol has –OH group bonded to a carbon which is bonded to two other carbon:
H OH H
H C C C H
H H H

3, tertiary alcohol has –OH group bonded to a carbon which is bonded to three other carbon:
H
H C
H
H
H
H C
C C
H
H OH H
The classification dictates what types of reactions the alcohol will undergo. Simple test can be performed to
determine which classification of alcohol is present.
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Ethers
An ether functional group is indicated by the presence of an oxygen atom sandwiched in-between two carbons.
The generic formula description of an ether is C-O-C. Ethers are named as each C group on either side of the
oxygen are alkyl groups followed with the word ether. The alkyl groups are alphabetized but in the grand scheme
of things, ethyl methyl either is the same compound as methyl ethyl ether.
CH3CH2-O-CH2CH2CH3
A 2 carbon alkyl group is an ethyl group (eth for 2 and yl for alkyl group)
A 3 carbon alkyl group is a propyl group (prop for 3 and yl for alkyl group)
Therefore the name is ethyl propyl ether
If both groups are the same on either side of oxygen then the alkyl group is named as a dialkyl group. For
example:
CH3CH2-O-CH2CH3
A 2 carbon alkyl group is an ethyl group, there are two ethyl groups therefore
Diethyl ether is the name for this species
Aldehydes and Ketones
Aldehydes and ketones are compounds that are very similar to one another and oftentimes confused with one
another when you are first starting out. Examine the two structures below and notice a subtle difference between
the aldehyde moiety and the ketone moiety.
O
O
CH3CCH3
CH3CH2CH
Aldehydes are always TERMINAL or on the end of the carbon chain
Ketones are always INTERNAL, they can never be on the end of the carbon chain.
Aldehydes are named the same as the parent alkane, but the e on the alkane name is dropped and al is added.
The longest carbon chain must contain the aldehyde functional group.
Ketones are named the same as the parent alkane, but the e is dropped on the alkane and one is added. Since the
carbonyl group is internal, and may vary in location, the exact location must be identified using the same
numbering system that we have been talking about.
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Concept Test
Name the following:
O
CH3CH2CH2CH2CH2CH
O
CH3CH2CH2CH2CH2CH2CH2CH
O
CH3CH2CH
O
CH3CH2CH2CCH2CH3
O
CH3CH2CH2CH2CCH3
O
CH3CH2CCH2CH2CH3
O
CH3CCH3
O
CH3CH2CH2CH2CCH2CH2CH3
O
CH3CCH2CH2CH2CH2CH2CH3
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Carboxylic Acids
Carboxylic acids and esters are like aldehydes and ketones in that they contain the carbonyl functional group.
O
O
-OH
C
carbonyl
O
C OH
hydroxyl
R'
carboxylic acid
C O C R
ester
Carboxylic acids are the acids found in organic molecules, the carbon based compounds necessary for life. The
term “carboxylic” is derived from carbonyl and “hydroxyl”, the two structures which make an organic acid.
None of the these carboxylic acids are classified as strong acids. Remember a strong acid is an acid which fully
dissociates in an aqueous environment. This is not to say an organic acid is not able to cause harm.
Small concentrations of hydrogen ion given off by organic acids are potent enough to kill most microscopic
organisms and cause tissue irritation and/or damage to larger organisms. Acetic acid is the acid found in vinegar,
a pickle stored in its brine may not spoil and be edible for years partly because of the organic acid from the vinegar
kills the bacteria which will cause spoilage.
Nomenclature:
carboxylic acids:
1.
2.
3.
count number of carbons in the longest carbon chain containing the –COOH group
replace the –e with the suffix –oic acid
compound containing multiple -COOH groups do not drop the –e but add a di- or tri- to the ending –
carboxylic acid or add a di- or tri- to the suffix –oic acid.
Examples:
Structural Formula
Condensed Structural
Formula
IUPAC
Common Name
O
CH3
O
C OH
CH3
CH2
C OH
HO C CH2
O
C OH
CH3COOH
CH3CH2COOH
HOOCCH2COOH
ethanoic acid
acetic acid
propanoic acid
-
propandioic acid
malonic acid
Esters:


1.
2.
3.
O
to create an ester an alcohol is reacted with a carboxylic acid
an ester is named for its starting materials, the acid and the alcohol
the first part names the alcohol, use the side chain abbreviation, i.e. methyl, ethyl…
the second part names the carboxylic acid
to end the second part change the –ic of the carboxylic acid to -ate
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Examples:
O
Structural
Formula
CH3
Condensed
Structural
Formula
IUPAC
Common Name
O
O
C O CH3
CH3
CH2
CH3
C O CH2 CH3
C O
CH3COOCH3
CH3CH2COOCH2CH3
CH3COOC6H5
methyl ethanoate
methyl acetate
ethyl propanoate
ethyl propyrate
phenyl ethanoate
phenyl acetate
Salts of Carboxylic Acids:
 to create a salt of a carboxylic acid, neutralize an organic acid with a strong base
1. change the name of the carboxylic acid suffix from –ic acid to –ate, just as you did with the ester
2. the first word will by the name with the cation, probably a metal
Examples:
Structural Formula
Condensed Structural
Formula
IUPAC
Common Name
CH3
C O Na
O
O
O
CH3
CH2
C O
C O
K
CH3COONa
CH3CH2COOK
C6H5COONa
sodium ethanoate
sodium acetate
potassium propanoate
-
sodium benzoate
phenyl acetate
Na
Preparation:
Carboxylic Acids:
The oxidation of a primary alcohol will lead through an aldehyde to a carboxylic acid.
H H
H O
H O
[O]
[O]
H C C OH
H C C H
H C C OH
H H
H H
H H
primary alcohol
carboxylic acid
aldehyde
Esters (esterification):
To create an ester an alcohol combines with a carboxylic acid in a dehydration reaction, which produces the ester
and a water molecule.
carboxylic acid
alcohol
O
H H
CH3
C OH
ester
HO C C H
CH3
H H
acetic acid
O
H H
C O
C C H
H H
ethyl ethanoate
ethanol
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H2O
Extra Information
Reactions:
Ionization:
The first definition of an acid is a proton donator. A carboxylic acid donates the hydrogen attached to the oxygen
fulfilling the definition of an acid.
O
O
CH3
CH3
C O H
H+
C O
This reaction has a double arrow. The reason is that organic acids are weak acids and form an equilibrium in a
solution. Only a small percentage of the acids give up their hydrogen. Once the equilibrium has been reached the
concentration of acid, hydrogen ion and anion remain constant. In the above case we have acetic acid, acetate
anion and hydrogen ion.
Acid/Base:
Just as you can neutralize an inorganic acid, organic acid can be neutralized. They same product is formed, a salt
and water. If sodium hydroxide is used to neutralize acetic acid the following reaction occurs.
O
O
CH3
C O H
ethanoic acid
NaOH
CH3
H
C O Na
sodium ethanoate
sodium hydroxide
H
O
water
Acid Anhydrides:
Two carboxylic acids can be combined to form an acid anhydrides. The term anhydride combines an- and hydride. The prefix an- means anti, in this form it is describing a loss. The loss is of water, which is where the
hydride portion comes to play. So, two carboxylic acids are
O
CH3
C O H
O
CH3
H O C CH3
O
O
C O
C CH3
H2O
Common Sources:
Carboxylic Acids:
The carboxylic acid function group can be found in all facets of nature. A few of the more common acids follow,
formic acid, a chemical defense for some ants, acetic acid, found in vinegar, propanoic acid, found in cheese,
butanoic acid, from spoiled butter, citric acid, from citric fruits, lactic acid, from dairy products, palmitic acid,
found in palm oil and stearic acid, from beef fat.
Esters:
The most utilized ester is that found in soap. Soap pre-dates history. The production is simple, boil a fat in wood
ash. The fat is actually the carboxylic acid, hence the name fatty acid. A fat like stearic acid, beef fat, would work
very well for producing soap. A component of wood ash is potassium hydroxide, which is a strong base. So, your
average caveman could easily produce soap by boiling some beef fat combined with ash from the campfire.
Other uses include dry cleaner fluids, pharmaceutical drugs, flavorings an scents. Methyl salicylate can be found
in wintergreen flavored mints.
Polymers
Polymers are an extremely important material in our world. Plastics are the most commonly used polymer, and
they are all around us, intertwined in our daily lives. How many of you brushed your teeth this morning? Well,
that was not horsehair on your toothbrush! (I hope!) How many of you put on clothes? Hopefully all of you. Ever
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paid attention to that material label inside your shirt or pants? Anyone wearing Nylon or Dacron or polyester
today? Because of their abundance in our society, as chemists, we should study the properties as well as structures
of polymer materials.
Polymers are extremely large molecules with molar masses exceeding 1.0 x 10 6 grams/mole. A polymer is a
material composed of many repeating units called monomers. Monomers are molecules which have the structural
ability to react and form a repeating sequence. The chemical structure of a monomer affects both the type of
polymer that it can form as well as the way in which the polymer forms in a chemical reaction. The main classes of
polymer materials are: addition polymers and condensation polymers.
An addition polymer is formed from a compound that contains a multiple bond. An initiator is used to open the
first monomer's multiple bond, but once the reaction starts, the open monomer reacts with other monomers in
order to form a polymer.
This reaction requires an initiator, like benzoyl peroxide or t-butyl benzoyl peroxide. Initiators are unstable
molecules that split apart into free radicals. Free radicals are highly reactive! They cause the first monomer’s double
bond to open and allow the polymerization process to begin. Often heat or ultraviolet light are needed before the
initiator will form free radicals; however, initiators (especially, peroxide initiators) should be handled with care
because they can explode if dropped with sufficient force.
Polymers all share some similar properties. These include: 1) the flexibility and structure 2) strength (try ripping
apart your nylon coat!) 3) the presence of crosslinks (usually covalent bonds) between polymer chains
Crosslinking can occur if there is a double bond or other reactive group present on a side chain. These reactive
areas can be used to create new bonding regions which will make a stronger, more rigid material. Crosslinking
restricts the ability of the individual polymer chains to slide past one another. Crosslinking can be thought of as a
three-dimensional network structure. Depending on the degree of crosslinking that occurs, different properties
result. Low levels of crosslinking, such as elastomers (e.g. rubber bands) are elastic and deformable. Highly
crosslinked materials, such as Bakelite (billiard balls) are obviously rigid and brittle.
Because we use so much plastic, recycling is an excellent way to conserve resources. A code for plastics was
established based on the most frequently used plastics (see chart below).
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Methyl Methacrylate:
Poly(methyl methacrylate), which lazy scientists call PMMA, is a clear plastic, used as a shatterproof replacement
for glass. The barrier at the ice rink which keeps hockey pucks from flying in the faces of fans is made of PMMA.
The chemical company Rohm and Haas makes windows out of it and calls it Plexiglas. Ineos Acrylics also makes it
and calls it Lucite. Lucite is used to make the surfaces of hot tubs, sinks, and the ever popular one piece bathtub
and shower units, among other things. PMMA is a member of a family of polymers which chemists call acrylates,
but the rest of the world calls acrylics. Another polymer used as an unbreakable glass substitute is polycarbonate,
but PMMA is cheaper!
When it comes to making windows, PMMA has another advantage over glass. PMMA is more transparent than
glass. When glass windows are made too thick, they become difficult to see through. But PMMA windows can be
made as much as 13 inches (33 cm) thick, and they're still perfectly transparent. This makes PMMA a wonderful
material for making large aquariums, whose windows must be thick in order to contain the high pressure millions
of gallons of water. In fact, the largest single window in the world, an observation window at California's
Monterrey Bay Aquarium, is made of one big piece of PMMA which is 54 feet long, 18 feet high, and 13 inches thick
(16.6 m long, 5.5 m high, and 33 cm thick).
PMMA is also found in paint. The painting on your right, Acrylic Elf was
painted by Pete Halverson with acrylic paints. Acrylic "latex" paints often
contain PMMA suspended in water. PMMA doesn't dissolve in water, so
dispersing PMMA in water requires we use another polymer to make
water and PMMA compatible with each other.
But PMMA is more than just plastic and paint. Often lubricating oils and
hydraulic fluids tend to get really viscous and even gummy when they get
really cold. This is a real pain if you trying to operate heavy equipment in
really cold weather. When a small amount of PMMA is dissolved in these oils and fluids, they do not get viscous
in the cold, and machines can be operated down to -100 oC! (the question is, can the human operating the machine
take that weather!!) PMMA is made by free radical vinyl
polymerization from the monomer methyl methacrylate.
As you can see from the picture, the structure of methyl methacrylate kind of looks like Massachusetts. But
Massachusetts does not polymerize, because there is only one.
NYLON 6,6:
Nylons are some of the most important fibers produced commercially. If you have ever slept in a tent or used a
toothbrush, you have used nylon fibers. But nylon can be more than just fibers. It is also used for self-lubricating
gears and bearings. Nylon-clay composites are used to make under-hood automobile parts.
The two most important kinds of nylon are nylon 6,6 and nylon 6. These two nylons have almost identical
properties. Both were invented in the late 1930s. Nylon 6,6 was discovered first. It was invented in the United
States by Wallace Carothers who was working for DuPont. Not long after that Nylon 6 was invented in Germany
by Paul Schlack who was working for I.G. Farben.
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Physical Properties
You may ask yourself, "Why does nylon act as it does?" You may ask yourself, "Why does nylon make such good
fibers?" The answer to both is pretty simple: intermolecular forces. When you are talking about nylons, the most
important intermolecular force is hydrogen bonding. The nitrogen-bonded hydrogens of one nylon chain will
hydrogen bond very strongly with the carbonyl oxygens of another nylon chain. These hydrogen bonds make
crystals of nylon very strong, because they hold the nylon chains together very tightly. Of course, these strong
crystals make strong fibers.
Unless it has been drawn into fibers, only about 20-30% of the nylon in a given sample is crystalline when in solid
form. The rest is in the amorphous phase. But even though it's non-crystalline, the chains are still bound strongly
to each other by hydrogen bonds. This combination of crystalline and strongly associated amorphous phases is
what makes nylon thermoplastics so tough. (This only applies to nylons used as thermoplastics, mind you. When
drawn into fibers nylons become almost entirely crystalline).
We all know that a lot of the nylon produced ends up as clothing. But it also ends up as other everyday things like
rope, tents, and toothbrush bristles. Sometimes nylon is used to make the belts that reinforce tires. Most
passenger car tires have steel belts, but tires for aircraft, trucks and off-road vehicles are often made of nylon.
Under the hood of your car you'll find nylon fibers reinforcing rubber belts, too.
Theory
Step-growth Polymerizations and Chain-growth Polymerizations
All polymerizations fall into two categories: step-growth polymerizations and chain-growth polymerizations. Both
step-growth polymerizations and chain-growth polymerizations are used to make nylons. Making nylon from a
diacid and a diamine is a step-growth polymerization.
So what is the difference between the two types of polymerization? There are some practical differences you
should know about for this experiment...
In a step-growth system, we start off with monomers. The monomers combine and grow into dimers, trimers,
tetramers, and so forth. The molecules get bigger and bigger, but only when you done (when the polymerization
reaches high conversion) do you have high molecular weight polymers.
But in a chain growth system, again you start off with monomers, but the monomers quickly form high molecular
weight polymers. There are high molecular weight polymers present in your test tube just after you start the
polymerization. There are no dimers, trimers, and other oligomers (many units) hanging around. A growing
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polymer chain grows so fast that it reaches high molecular weight quickly, and it does not spend any real length of
time as an oligomer.
Polycondensations
There is another way to describe polymerizations other than the step-growth/chain-growth system. There is also
the condensation/addition system. The most important thing you need to know about this system is that it
classifies all polymerizations as polycondensations or polyadditions. Polycondensations are polymerizations in
which a small molecule by-product is produced. The by-product is usually something like water, HCl, or once in
awhile NaCl. Polyadditions on the other hand are polymerizations in which no by-product is produced.
Polycondensation can be used to make nylons. The simplest polycondensation for making nylons is the
polymerization of a diacid and a diamine. This reaction might not normally go to high conversions (make a lot of
nylon as the product), but by removing the water by-product, we can force this reaction go to higher conversions.
Removing water makes the reaction go to high conversion thanks to LeChatlier's Principle.
Our preparation of nylon uses the diacid, and is a condensation polymer. It is produced when a diamine and a
diacid chloride react. The small molecule produced is hydrochloric acid.
Today in lab, you will react 1,6-hexanediamine and adipoyl chloride to form nylon-6,6 and HCl. The structures for
the monomers and polymer are shown below.
The Silly Polymer:
Silly Putty is a dilatant compound, a silicone based polymer that is highly elastic, exhibits high bounce, can be
easily molded, yet can hold it shape while at rest. It is non-toxic and non-irritating to the skin.
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The history of silly putty is quite amusing. In 1943 James Wright, an engineer, was attempting to create a synthetic
rubber. He was unable to achieve the properties he was looking for and put his creation (later to be called silly
putty) on the shelf as a failure. A few years later, a salesman for the Dow Corning Corporation was using the putty
to entertain some customers. One of his customers became intrigued with the putty and saw that it had potential as
a new toy. In 1957, after being endorsed on the "Howdy Doody Show", silly putty became a toy fad. Recently new
uses such as a grip strengthener and as an art medium have been developed. Silly putt even went into space on the
Apollo 8 mission.
The polymers in silly putty have covalent bonds within the molecules, but hydrogen bonds between the molecules.
The hydrogen bonds are easily broken. When small amounts of stress are slowly applied to the putty, only a few
bonds are broken and the putty "flows". When larger amounts of stress are applied quickly, there are many
hydrogen bonds that break, causing the putty to break or tear.
If a substance springs back to its original shape after being twisted, pulled, or compressed, it is most likely a type of
polymer called an elastomer. The elastomer has elastic properties (i.e., it will recover its original size and shape
after being deformed). An example of an elastomer is a rubber band or a car tire.
The liquid latex (Elmer's glue) which you use contains small globules of hydrocarbons suspended in water. The
silly putty is formed by joining the globules using sodium borate (a cross-linker). The silly putty is held together
by very weak intermolecular bonds that provide flexibility around the bond and rotation about the chain of the
cross-linked polymer. If the cross-linked bonds in a polymer are permanent, it is a thermosetting plastic. If the
bonds are non-permanent, it can be considered either thermoplastic or an elastomer.
The covalent bonds along the chain are strong, but the bonds between chains are normally weak. However,
additives such as borax allow the formation of strong "cross-links" between chains, such as C-B-C. As the number
of cross-links increases, the material becomes more rigid and strong.
Borax crosslinking in a polymer
I’m Melting . . .
Polystyrene is an inexpensive and hard plastic, and probably only polyethylene is more common in your everyday
life. The outside housing of the computer you are using now is probably made of polystyrene. Model cars and
airplanes are made from polystyrene, and it also is made in the form of foam packaging and insulation. Clear
plastic drinking cups are made of polystyrene, so are a lot of the molded parts on the inside of your car, like the
radio knobs. Polystyrene is also used in toys, and the housings of things like hairdryers, computers, and kitchen
appliances. What we commonly call styrofoam, is actually the most recognizable form of foam polystyrene
packaging. Styrofoam ® is a Dow Chemical Co. trademarked form of polystyrene foam insulation, introduced in
the U.S. in 1954. Styrofoam® is a trademarked name, the real name of the product is foamed polystyrene.
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Polystyrene is a vinyl polymer. Structurally, it is a long hydrocarbon chain, with a phenyl group attached to every
other carbon atom. Polystyrene is produced by free radical vinyl polymerization, from the monomer styrene.
Polystyrene is a polymer which is cross-linked to provide extra stability in keeping its shape. Air (or other common
gas) can be blown into molten polystyrene (plastic) to create a light and foamy material called styrofoam. This airfilled product is good for packing and insulation. Water tends to dissolve molecules that contain OH groups
(hydrophilic), but styrofoam does not have OH groups associated with them which makes styrofoam cups good to
drink out of! However, styrofoam cups cannot hold all types of liquid.
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