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Notes: Organic Chemistry & Alkanes
History:
Vital Force Theory: organic molecules can only be created by living organisms
...
While working
the laboratory he succeeded in synthesizing an organic compound, urea, previously observed
only in living tissue
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He evaporated a solution of Ammonium Cyanate to produce Urea
...
There are well over a million
synthetic organic compounds
...

Carbon is a Lego like element
...
Like the two below, octane on the left and a steroid precursor on the right
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Hybridization:
The 4 bonds carbon forms is explained by Linus Pauling’s theory of hybridization
...


2p

2s

1s
From the looks of this diagram, carbon might form 3 bonds as appears to be nowhere for a 4 th
bond to form
...


This new energy level diagram is draw below

This shows four open orbitals, allowing for the formation of four bonds
...
When carbon atoms are bonded using all single bonds the below shape forms
from the combination of one s orbital and three p orbitals
...

These shapes are verified by an analysis technique named X-Ray Crystallography
...
The resulting pictures have shown this
tetrahedral shape
...
This shape is formed by the repulsion of the electrons which
surround all atoms
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The angle between these bonds is
109
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The blue balloon looking objects represent the orbitals where the four electrons in
carbons second energy level reside
...
Each of the four electrons have
equal energy and are all in the same orbitals, they have been moved to the same “Shell” instead
of having the 2s electrons located inside or underneath the 2p electrons
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The addition of one sphere and three
dumbbell shapes produces this tetrahedral shape
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2
...

4
...

6
...

8
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Flammable
High Vapor Pressure
Odorous
Covalently Bonded
Non-Polar – functional groups can change these from non-polar to polar or cause the
molecule to be bi-polar
...
The most simple
alkanet consists of only carbon and hydrogen atoms connected by single bonds
...

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
...
The governing body is “The
International Union of Pure and Applied Chemistry”, or IUPAC for short
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As a scientific, international, non-governmental and objective body,
IUPAC can address many global issues involving the chemical sciences
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One of their main
functions is to objectively create rules for naming compounds in the most simplified manner
possible
...

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
...
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
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The suffix for the alkane family is –ane
...
)
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
...
Other times you need to see the structure drawn out,
this is referred to as the structural formula
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Another is the condensed structural formula, this shows the connections in
around about manner
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This simplified drawing
assumes you know that carbon atoms make 4 bonds and that if you do not see a bond drawn
assume a hydrogen is occupying the undesignated bond
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Examples:
Chemical Formula:
C4H10

Condensed Structural Formula:
CH3CH2CH2CH3

Structural Formula:
H H H H
H C

C

C

C

Line Structure:
H

H H H H

Rules:
1
...
Number the chain with the end nearest the first subsistent carbon #1
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Give the location of the alkyl subsistent by the number of the main-chain carbon that it is
attached to
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Put the Constituents in alphabetical order (i
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ethyl before methyl)
5
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between numbers and words add a dash
b
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Also creates different properties
for the molecule
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These molecules are isomers of the same chemical formula
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butane
2-methyl propane (isobutane)

More Examples:

hexane

2-methyl pentane

2,3-dimethyl butane

3-methyl pentane

2,2-dimethyl butane
not
3,3-dimethyl butane

Chemical Equivalence – non-isomers:
When one first begins learning how to name organic compounds they typically have a difficult
time recognizing when two molecules are actually the same molecule
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Let’s look at
the following two structural formulas:
H H
F H
F

C C H

H C C H

H H
H H
These two molecules look different but they are actually the same
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So, the difference
between the two above molecules is simply that the carbon-carbon bond is rotated to a different
position
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Let’s look a this molecule a little more, by the way, its name is fluoroethane
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The following structural drawings will all actually be of this same
molecule:
H H
F

C C H

F

H

H C C H

H H
H C C H

H H

H H

H H

H F

H H

H C C F

H C C H

H C C H

H H

H H

H F

F

H

Yes, they look different, try using a molecular modeling kit and proving to yourself that yes
indeed, these are all the same
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You simply twist the carbon-carbon bond or
flip the molecule around
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I just added another fluorine to our
fluoroethane molecule
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This means that both fluorines
will react, chemically, in exactly the same manner
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Both fluorines have the exact same description, the fluorines are bonded
to a carbon that is singly bonded to another carbon and also bonded to two other hydrogens
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If we look at the hydrogens on this molecule we can demonstrate that they too are all chemically
equivalent
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Looking back to the fluoroethane we can see that not all of the hydrogens are chemically
equivalent
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The following molecules have two colored atoms, these colored atoms are listed as either
chemically equivalent or non-equivalent
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If the two atoms
you are comparing have symmetry between themselves on the molecule, they are probably
chemically equivalent
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By this I mean they commonly form rings
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It is a hexane molecule that has come around back onto itself
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H
H
H
H
C
C H
H C
H C
C H
C
H
H HH

C6H12

Sources of Alkanes:
Crude oil is the main supplier
...
Collection equipment is stationed at various levels ready to remove hydrocarbons of
various masses
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Natural gas is the name given to the lightest of the alkanes, this gas is a combination of
methane, ethane and propane
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See picture of refinement tower below
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But his process is time consuming and expensive
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Synthetic can easily be 15 times more expensive
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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
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This phenomenon in your conventional internal
combustion engine is called “Engine Knock
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The timing of ignition is very important
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Pistons are rising then being forced down by
the explosion of these hydrocarbon vapors mixed with oxygen gas from the atmosphere
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The knock occurs when some of the fuel enters the cylinder and ignites before the spark plug
has fired
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The reason for the premature ignition is due to the varied
flammability of the different hydrocarbons found in gasoline
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You have no doubt seen the different ‘flavors’ of gasoline available at any gas station
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The higher the number the less chance of
knocking
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2,2,4-trimethylpentane, common name isooctane, earns an octane number of 100
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The more branching the better the fuel
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The above
isooctane could have been octane cracked and reformed as isooctane
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Is allows it to withstand higher temperatures as it waits to be ignited
by the firing spark plug
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Reactions of Alkane:
Combustion:
C3H8(g) + O2(g)  CO2(g) + H2O(g) + heat
complete – occurs in high oxygen environments

C3H8(g) + O2(g)  CO2(g) + CO(g) + H2O(g) + less heat
incomplete – occurs in low oxygen environments

Halogenation:
C3H8(g) + Br2(l)

uv


C3H7Br (g) + HBr(g)

Dehydrogenation:
C3H8(g)

Pt


C3H6(g) + H2(g)

Organic Functional Groups:
Organic molecules can be very complex, not only for their ability to branch off but also for
specialized groupings of atom each of which give molecules special properties
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One molecule may have more than one of these groups giving
the molecule different properties
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Another Classification for Carbons:
•

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
•

quaternary carbon is bonded to four other carbons
o the center red carbon only
H

H C

H

H

H

H C

C C

H

H

H C

H

H

H



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