The importance of
organic chemistry
Many areas rely on organic
chemistry, including:
• Biology
• Petroleum
• Polymers
• Genetic Engineering
• Agriculture
• Pharmacology
• Consumer Products
Importance of carbon
• Basis for all life.
• Form stable covalent bonds to other
carbon atoms - catenation.
• Can form single, double and triple
bonds.
• Long carbon chains can be produced.
• Will bond with many other elements.
• A HUGE number of compounds is
possible.
Hydrides of carbon
Catenation
The formation of chains of atoms of the
same element.
This key feature of carbon permits a vast
number of compounds to exist.
One simple class of compound is the
alkane which has only C, H and single
bonds.
H
H
C
H
H
methane
H
H
H
C
C
H
H
H
ethane
H
H
H
H
C
C
C
H
H
H
H
propane
H
H
H
H
H
C
C
C
C
H
H
H
H
butane
H
Formulas and models
Organic molecules can have very
complex structures.
A number of formats are used to
represent organic compounds.
Each has its own advantages but the
goal is the same, to accurately
describe the structure of a compound.
Lets look at some different
representations.
Formula
Condensed structural formula
• Shorthand way of writing formula.
• Lists all atoms in order and tells how
they are bound together.
Example.
Propane
CH3CH2CH3
This is a convenient format for
describing a molecule using text.
Structural (Constitutional) isomers
Compounds with the same number and type
of atoms but with different arrangements.
Molecular Formula
C5H12
Condensed structural formulas.
CH3CH2CH2CH2CH3
pentane
CH3CH(CH3)CH2CH3 2-methylbutane
(CH3)4C
2,2-dimethylpropane
All are structural isomers of C5H12.
Line formula
• Similar to structural formula.
• Each line represents a bond.
• Carbons are assumed to be present at the end of
each line segment.
• Hydrogen is not shown when bound to carbon.
OH
H2 H2
C C
H2C
CH2
C C
H2 H2
N
H2 H2
C C
H2C
H2C
C C
H2 H2
H
H2 H2
C C
OH
H2C
N
C C
H2 H2
H2 H2
C C
H
H2C
H2C
C C
H2 H2
H2
C
CH3
Models
Three dimensional representations
Ball and Stick
Space Filling
Both are models of propane.
Alkanes
Simplest members of the hydrocarbon family.
• contain only hydrogen and carbon
• only have single bonds
All members have the general formula of
CnH2n+2
Twice as many hydrogen
as carbon + 2
Alkanes
First four members of the alkanes
Name
Methane
# of C
1
Condensed formula
CH4
Ethane
2
CH3CH3
Propane
3
CH3CH2CH3
Butane
4
CH3CH2CH2CH3
Called a homologous series
“Members differ by number of CH2 groups”
Alkanes
Physical Properties
Nonpolar molecules
Not soluble in water
Low density
Low melting point
Low boiling point
These go up
as the number
of carbons
increases.
12.7 Properties of Alkanes
Odorless or mild odor; colorless; tasteless;
nontoxic
Flammable; otherwise not very reactive
The first four alkanes are gases at room
temperature and pressure, alkanes with 5–
15 carbon atoms are liquids; those with 16 or
more carbon atoms are generally lowmelting, waxy solids.
12
22 - 12
The boiling and melting points for the straightchain alkanes increase with molecular size.
13
22 - 13
Alkanes
Name
bp, oC
mp, oC
Density at 20 oC
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
-161.7
- 88.6
- 42.2
-0.5
36.1
68.7
98.4
125.6
150.7
174.0
-182.6
-182.8
-187.1
-135.0
-129.7
- 94.0
- 90.5
- 56.8
-53.7
-29.7
0.000 667
0.001 25
0.001 83
0.002 42
0.626
0.659
0.684
0.703
0.718
0.730
22 - 15
Sources of alkanes
Alkanes can be obtained by refining or
hydrogenation of:
petroleum
shale oil
coal
Low molecular mass alkanes can be
obtained directly from natural gas.
Reactions of alkanes
Combustion
CH4(g) + 2O2(g)
CO2(g) + 2H2O(g)
Many alkanes are used this way - as fuels
Methane
-
natural gas
Propane
-
used in gas grills
Butane
-
lighters
Gasoline
mixture of many
hydrocarbons, not all alkanes
Reactions of alkanes
Halogenation
A reaction where a halogen replaces one or
more hydrogens.
CH4(g) + Cl2(g)
heat or light
CH3Cl(g) + HCl(g)
Used to prepare many solvents
• dichloromethane - paint stripper
• chloroform - once used as anesthesia
• 1,2-dichloroethane - dry cleaning fluid
Organic nomenclature
Organic molecules can be very complex.
Naming system must be able to tell
• Number of carbons in the longest chain
• The location of any branches
• Which functional groups are present and
where they are located.
The IUPAC Nomenclature System provides a
uniform set of rules that we can follow.
Prefix
MethEthPropButPentHexHeptOctNonDec-
Carbons
1
2
3
4
5
6
7
8
9
10
Base names
I see much
memorization in
your future!
Naming Alkanes
IUPAC Rules
Acylcic, saturated hydrocarbons end in “-ANE”
Named by the number of carbons in the “chain”
The Root is the longest carbon chain
Substituents or alkyl groups named by the number
of carbons
Substituents are identified by the number of the
carbon and how many of that type of group.
(mono = 1, di = 2 , tri = 3, tetra = 4 etc.)
Two or more different substituents are listed
alphabetically
ethyl before methyl
Names are one word. Numbers are separated by
commas and names are separated by hyphens.
There are no spaces between the substituent
and the root names
22 - 21
12.6 Naming Alkanes
The system of naming now used is one devised
by the International Union of Pure and
Applied Chemistry, IUPAC.
In the IUPAC system for organic compounds, a
chemical name has three parts: prefix,
parent, and suffix.
22 - 22
Drawing Organic Structures
Condensed structure: A shorthand way of
drawing structures in which C-C and C-H
bonds are understood rather than shown.
22 - 23
Branched-chain alkanes
STEP 1: Name the main chain. Find the longest
continuous chain of carbons, and name the
chain according to the number of carbon
atoms it contains.
The longest chain may not be immediately
obvious because it is not always written on
one line; you may have to “turn corners” to
find it.
24
22 - 24
STEP 2: Number the carbon atoms in the main chain.
Begin at the end nearer the first branch point:
► STEP 3: Identify the branching substituents, and
number each according to its point of attachment to
the main chain:
25
22 - 25
► If there are two substituents on the same carbon,
assign the same number to both. There must always be
as many numbers in the name as there are
substituents.
STEP 4:Write the name as a single word, using
hyphens to separate the numbers from the
different prefixes and commas to separate
numbers if necessary. If two or more different
substituent groups are present, cite them in
alphabetical order.
26
22 - 26
If two or more identical substituents are
present, use one of the prefixes di-, tri-, tetra-,
and so forth, but do not use these prefixes for
alphabetizing purposes.
22 - 27
Examples
C-C-C-C-C-C
|
|
C-C C
C-C-C-C C-C-C
|
|
C-C-C-C-C-C-C
|
C
C-C-C-C-C-C-C
|
|
C-C C
Examples
C-C-C-C-C-C
|
|
C-C C
3,5-dimethylheptane
C-C-C-C C-C-C
|
|
C-C-C-C-C-C-C
|
C
C-C-C-C-C-C-C
|
|
C-C C
Examples
C-C-C-C-C-C
| |
C-C C
3,5-dimethylheptane
C-C-C-C C-C-C
|
|
C-C-C-C-C-C-C
|
C
C-C-C-C-C-C-C
|
|
C-C C
3-ethyl-5-methylheptane
Examples
C-C-C-C-C-C
|
|
C-C
C
3,5-dimethyl heptane
C-C-C-C C-C-C
|
|
C-C-C-C-C-C-C
|
C
C-C-C-C-C-C-C
|
|
C-C C
3-ethyl-5-methylheptane
2,3,3,7,8-pentamethyldecane
Another example
Name the following.
(CH3)2CHCH2CH2CH(CH3)2
This is a condensed structural formula.
First convert it to a carbon skeleton, leaving
out the hydrogens.
Another example
(CH3)2CHCH2CH2CH(CH3)2
C
C
|
|
C-C-C-C-C-C
Now name it!
Another example
C
C
|
|
C-C-C-C-C-C
1. Longest chain is 6 - hexane
2. Two methyl groups - dimethyl
3. Use 2,5-dimethylhexane
The situation is more complex for larger alkanes.
There are two different three carbon alkyl groups,
there are four different four carbon alkyl
groups.
22 - 35
22 - 36
Substituents to a Carbon Chain
Alkyl Chains
Named by number of carbons
Straight chains
Branched chains
iPr
sBu
iBu
tBu
Halides
Branch name
Halohydrocarbons
22 - 37
Naming alkyl halides
1. Follow the same system as with alkanes.
2. Give the name and carbon number for the
halide just like a side branch.
C-C-F
1-fluoroethane
C-C-C
C-C-C-C-C
|
|
Cl
C-Br
2-chloropropane
1-bromo-2-ethylbutane
Practice
2,3 dimethylpentane
3-ethyl-4-methlylheptane
4-propyl-2,2,3,3-tetramethyloctane
4-isopropyloctane
22 - 39
Drawing and Naming Cycloalkanes
Ring structures are possible and very
important in organic chemistry.
A more streamlined way of drawing structures
is often used in which cycloalkanes are
represented simply by polygons.
40
22 - 40
In line structures, a C is located at every
intersection, and the number of H atoms
necessary to give each C four covalent bonds is
understood. Methylcyclohexane, for example,
looks like this in a line structure:
41
22 - 41
STEP 1: Use the cycloalkane name as the
parent.
named as alkyl-substituted cycloalkanes
rather than as cycloalkyl-substituted
alkanes.
If there is only one substituent on the ring
it is not necessary to assign a number
because all ring positions are identical.
42
22 - 42
STEP 2: Identify and number the
substituents.
Start numbering at the group that has
alphabetical priority,
Proceed around the ring in the direction that
gives the second substituent the lower
possible number.
43
22 - 43
1,2,4,4,5-pentachlorocylooctane.
Draw
Start by drawing an octagon.
Number the carbons and draw in substituents
22 - 44
Cyclic Alkane Properties
Cyclic compounds have ring strain.
They are more eclipsing than linear molecules
and can’t rotate to relieve strain.
Also to convert the tetrahedral bond angles to the
angles necessary for a ring causes bond-angel
strain.
Cyclopropane is planer and unstable.
Cyclobutane is not planer but “puckered”
Cyclopentane has the “envelope” and “half-chair”
shapes rather than being planer.
Cyclohexane is not planar as well, has “chair”
and “boat” formations.
All to relieve stress and lower potential energy.
22 - 45
Conformations of Cylcohexane
Axial groups are close in space, so the smallest substituent
will be in the axial postion
Chair Conformation
22 - 46
The Chair Conformation Can Flip
All the axial positions become equatorial after a fli
22 - 47
Methyl Cylohexane
↔
Flip
Which confirmation is favored?
Can you draw a Newman projection of carbon 1 and 2
for each conformation?
22 - 48
Multiple bonds
Another key feature of carbon is its
ability to form double and triple bonds.
This can be between two carbons
alkenes (C=C) and alkynes (C C)
It can also be between carbon and
another element.
C=O
C=NC N
Ethane, C-C single bond
Rotations
Since the central atom can rotate, then the
hydrogens can line up (eclipsed) or be
staggered
There is a potential energy difference
between the two positions.
The change in energy is called torsional
energy or rotational energy
Due to this, the molecule is more likely to be
staggered rather than eclipsed.
The bigger the carbon chain and groups that
would be eclipsed, the harder the rotation
is.
Called steric hindrance.
Gauche and anti – 4 carbons or more.
22 - 51
Ethene or ethylene, C=C double bond
Ethyne or acetylene, C C triple
bond
Naming alkenes and alkynes
1. All multiple bonds must be included as
part of the main chain, even if it is not
physically the longest chain.
2. Multiple bonds take priority over
substituted groups in determining the
lowest number.
3. Follow the same system as with alkanes.
C C-F
C-C-C-C=C
|
fluoroethyne
C-Br
4-bromo-3-ethyl-1-butene
Alkanes and Saturated Hydrocarbons
Saturated fat and unsaturated fat
Unsaturated means there is a C=C
Polyunsaturated means there are 2 or more
C=C
How can you tell if a hydrocarbon is saturated?
Why are they healthier to eat?
What phase to they tend to be?
22 - 55
Alkenes and Alkynes
Simple alkenes are made in vast quantities in
the petroleum industry by thermal
“cracking” of the alkanes in petroleum.
Most of the organic chemicals used in making
drugs, explosives, paints, plastics, and
pesticides are synthesized by routes that
begin with alkenes.
56
22 - 56
Classification of Unsaturated
Hydrocarbons
Alkene – has a carbon carbon double bond
Diene- has 2 C=C bonds
Conjugated, C=C-C=C, (interacting ∏ bonds)
Cummulated, C=C=C
Nonconjugated diene, C=C-Cn-C=C,
(noninteracting ∏’s)
Conjugated is much more stable than
nonconjugated.
22 - 57
Which carbons are conjugated?
http://www.3dchem.com/3dmolecul
e.asp?ID=103
22 - 58
Nomenclature of Alkenes and Alkynes
Ending for C=C is -ene, Ending for C=C is –yne
Compounds with both are –enynes.
Select longest chain with the unsaturation
Number the chain so unsaturation has the lowest
number
1. The name starts with the “smallest number”
2. If there are two double bonds, use the order
with the lowest number
3. If there are a double and a triple bond, the
order with the double bond being lowest has
priority
22 - 59
Naming Alkenes and Alkynes
In the IUPAC system, alkenes and alkynes are
named by a series of rules similar to those used
for alkanes. The parent names indicating the
number of carbon atoms in the main chain are
the same as those for alkanes, with the -ene
suffix used in place of -ane for alkenes and the yne suffix used for alkynes.
STEP 1: Name the parent compound. Find the
longest chain containing the double or triple
bond, and name the parent compound by adding
the suffix -ene or -yne to the name for the main
chain.
60
22 - 60
Name the parent compound. Find the longest chain
containing the double or triple bond, and name the
parent compound by adding the suffix -ene or -yne to
the name for the main chain.
The number of multiple bonds uses a numerical prefix
diene = 2 double bonds
triene = 3 double bonds and so on…tetra, penta, hexa,
61
22 - 61
Number the carbon atoms in the main chain,
beginning at the end nearer the multiple
bond. If the multiple bond is an equal
distance from both ends, begin numbering at
the end nearer the first branch point.
62
22 - 62
Write the full name.
Assign numbers to the branching substituents,
and list the substituents alphabetically.
Use commas to separate numbers and
hyphens to separate words from numbers.
Indicate the position of the multiple bond in the
chain by giving the number of the first multiplebonded carbon. If more than one double bond is
present, identify the position of each and use
the appropriate name ending
for example, 1,3-butadiene and 1,3,6heptatriene
For historical reasons, there are a few alkenes
and alkynes whose names do not conform
strictly to the rules.
63
22 - 63
Alkenes and alkynes differ from alkanes in
shape because of their multiple bonds.
Methane is tetrahedral, ethylene is flat and
acetylene is linear, as predicted by the
VSEPR model.
Unlike the situation in alkanes, where free
rotation around the single bond occurs,
there is no rotation around the double
bonds..
64
22 - 64
Stereoisomers
Structural isomers are not the only
types that can exist.
Stereoisomers have
• the same order and types of
bonds.
• different spatial arrangements.
• different properties.
Many biologically important
compounds, like sugars, exist as
stereoisomers. Your body can tell
the difference.
Stereoisomers
Two kinds of stereoisomers exist.
Cis-trans (Geometric) isomers
When a double bond exists between
carbons or carbons form a ring, a
molecule can exist in two geometric
forms.
Optical isomers
When molecules can exist as mirrorimage isomers or enantiomers.
Cis and Trans Isomerism
Configurational stereoisomers
Cis –same side
Trans – opposite
sides
They are different
compounds
No free rotation
22 - 67
Cis–trans isomerism
whenever each double-bond carbon is
bonded to two different substituent
groups.
If one of the double-bond carbons is
attached to two identical groups, cis–trans
isomerism is not possible.
68
22 - 68
Retinal and sight
cis-retinal
Light causes a
change from cisto trans-. This is
how we see.
O
light
several steps Several enzymes
O
trans-retinal
are required
to convert
trans-retinal
Back to the
cis-form.
3-D models of retinal
cis-
trans-
Enantiomers
Pairs of stereoisomers
Sometimes designated by D- or L- at the start
of the name.
They are mirror images that can’t be
superimposed.
If you don’t believe it,
give it a try!
Enantiomers
L-
and D- glyceraldehyde
CHO
CHO
HO
H
H
OH
C
C
CH2OH
CH2OH
CHO
CHO
HO
H
CH2OH
H
OH
CH2OH
Enantiomers
Stereocenter.
Chiral center or asymmetric carbon - four
different things are attached to it.
Cl
|
I- C - F
|
Br
Chiral center
A molecule that has one stereocenter exists
as a pair of enantiomers.
Examples
Is the ‘red’ carbon a stereocenter?
H
C=O
H
H3C- C-OH
HO
CH2CH3
I
Cl
C=C
Br
F
H
H
H3C- C-OH
H
|
C=O
|
H-C-OH
|
CH2OH
HH H
H2N-C-C-C-SH
Cl H Cl
Classifying organic compounds
Functional Groups take priority!!!
Functional group - Specific combination of atoms
that gives a known type of behavior.
Alcohols
R-OH
-ol
Acids
R-COOH
-oic Acid
Amines
R-NH2
-amine
Ketones
R(C=O)R’
-one
Aldehydes
R-CHO
-al
Amides
R-CONH2
-amide
Ethers
R-O-R’
ether
Esters
R-OO-R’
-oate
Thiols
R-SH
-thiol
Nitriles
R-CN
-nitrile
C-C-C-C-O-H
Alcohol example
The IUPAC system deals with functional groups
two different ways.
Base contains 4 carbon
- alkane name is butane
- remove -e and add -ol
alcohol name - butanol
OH is on the first carbon so…..
1-butanol
alternate name: 1-hydroxylbutane
Acid example
Example: CH3CH2COOH
1. Longest chain containing carbonyl is 3,
propane
2. The -e ending is replaced with -oic acid,
propanoic acid
Physical properties
Optical activity
ability to rotate plane-polarized light.
dextrorotatory
- rotate clockwise
- use + symbol
- usually D isomers
levorotatory
- rotate counterclockwise
- use - symbol
- usually L isomers
Plane polarized light
Light is passed through a polarized filter.
A solution of an optical isomer will rotate the
light one direction.
Organic Reactions
Pyrolysis
Substitution
-halogenation – with a halogen
-SN2 – with a nucleophile
-SN1 or hydrolysis (solvolysis) – substitution by solvent
E1 - Elimination – removes halogen and makes alkene
E2 – Elimination – same as E1 but different mechanism
Hydrogenation – double bond eliminated by hydrogen
Hydration – double bond is eliminated and makes an
alcohol.
Dehydration – water is released.
Electrophilic addition – double bond is broken by a strong
acid.
Polymerization – taking alkenes and linking them into
(essentially) unending chains.
22 - 81
REDOX and organics
Oxidation is defined as any process that adds
electronegative atoms or removes
hydrogen.
Reduction is any process that adds hydrogen
and removes electronegative elements.
22 - 82
Homo and heterolytic cleavage
When a bond is broken, each fragment gets one
of the electrons from the bond and is left with
an extra unpaired electron
This is called homolysis or homolytic cleavage.
The result is two free radicals
Usually free radicals are intermediates and are
high energy.
A-B → A. + B.
If a bond is broken and both electrons go to one
fragment, then they both become ions
This is called heterolytic cleavage.
A-B → A+ + :B22 - 83
Pyrolysis
When alkanes are exposed to high temperatures,
C-H and C-C bonds begin to break leaving two
radicals.
The radicals can combine to form smaller chains.
Process is called cracking.
Heat can also cause hydrogen to be lost from the
radical leaving an alkene
Called hydrogen abstraction.
CH CH . + CH CH CH .→ CH CH + CH CH=CH
3
2
3
2
2
3
3
3
Zeolytes (catalysts like sodium aluminosilicates)
help specialize what products will be made.
2
22 - 84
Hyperconjugation
When the electron is removed from the molecule,
an sp3 orbital is left half empty.
The electron in the orbital delocalizes into a p
orbital leaving the other bonds in a planar
formation.
Resonance and hyperconjugation are forms of
delocalization of electrons.
Resonance is of a π bond overlap of p-orbitals
Hyperconjugation is delocalization with σ bonds.
22 - 85
Substitution Reaction
A general reaction type in which an atom or
group of atoms in a molecule is replaced by
another atom or group of atoms.
Halogenation reactions are one type:
86
22 - 86
Halogenation
Activity series determines which halogen is most
likely to react and substitute
Fluorine is exothermic, the rest are increasingly
endothermic.
UV light breaks the halogen bond enabling the
reaction.
Secondary carbons are more likely to substitute
than primary.
Tertiary are more likely than secondary.
22 - 87
SN2 mechanism
Reaction mechanisms provide a powerful way
to organize the vast amount of information
about organic reactions.
SN2 mechanism
• One very important reaction mechanism.
• The symbol (SN2) stands for substitution
nucleophilic bimolecular.
Nucleophile
“Nucleus loving.” A species that is
attracted by a positive charge.
OH-, I-, NH3, CH3O-, NC-
Example
HO- + CH3Br (aq)
For this reaction:
SN2 mechanism
CH3OH (aq) + Br-
• HO- is the nucleophile. Increases with
increasing negative charge, decreases to
right on periodic table
• CH3Br is the substrate - a species that
undergoes reaction.
• Br- is the leaving group. Because it is
replaced by HO-. Weak bases are good
leaving groups.
SN2 mechanism
The mechanism takes place in a single step.
This is supported by the observed rate law.
Rate = k [HO-][CH3Br]
SN2 reactions also take place with inversion
of configuration.
CH3
CH3
Cl
+ HO -
+ Cl OH
SN2 mechanism
H
H
HO
d+
-
C
H
d-
Br
H
To account for the inversion,
the nucleophile must approach
from the back of the carbon
The nucleophile acts as a Lewis
base and the substrate as a
Lewis acid.
HO
Br
H H
H
d-
HO
d+
+ Br
C
H
H
-
SN2 mechanism
Predicting whether an SN2 reaction will occur
is possible.
The SN2 reaction
Nuc:- + RX
RNuc + X-
is similar to a Bronsted-Lowry acid base
reaction
B:- + HX
HB + X-
SN2 mechanism
To predict whether a SN2 reaction will occur,
you must consider the relative base
strength of the nucleophile and the leaving
group.
If the nucleophile is a stronger base, the
reaction will occur.
Relative base strength
OH- > Cl- > Br- > ISecond order based on concentration of the
base and the halide.
Hydrolysis (SN1)
Haloalkane reacts with water solvent.
Halogen ionizes away from a carbon leaving a
carbocation.
Tertiary carbocations are the best while
primary are the worst.
Due to hyperconjugation the positive charge
is stabilized in the tertiary formation.
Polar water is attracted to carbocation.
Extra hydrogen is attracted to next water
molecule to create a hydronium ion.
First order based on concentration of halide.
22 - 94
E1 Elimination
Haloalkanes react with a base or nucleophile.
Alternate SN1 pathway.
Instead of adding water, it kicks out another
proton (H+) and forms a double bond between
carbons in its place.
Leaves you with an alkene and a halogenated
acid.
Weak bases give substitutions SN1and SN2,
strong bases give eliminations E1.
First order reaction: only dependent on the
concentration of the halide.
22 - 95
E2 - Elimination
Second order reaction due to concentration
of both the halide and the base.
Base attacks a hydrogen on a carbon away
from the halide.
Hydrogen leaves donating its electron pair to
the carbon giving it four pairs.
Carbon makes double bond with the other
carbon which causes the release of the
halogen ion.
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Hydrogenation
A carbonyl group from an aldehyde or a
ketone or a double bond in an alkene is
attacked by hydrogen gas or some other
hydride in the presence of a catalyst.
Catalyst is usually heterogeneous (insoluble)
like platinum, palladium, or nickel deposited
on carbon.
Results in an alcohol when an aldehyde or
ketone is involved, and an alkane when an
alkene is involved.
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Hydration: The addition of water, in the
presence of a strong acid catalyst, to a
multiple bond to give an alcohol product.
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Dehydration
A strong acid is added to an alcohol making a
halide and water.
HBr + C2H5OH → C2H5Br + H2O
A carboxylic acid and alcohol react in the
presence of an acid to make an ester.
Called esterfication.
An alcohol in acid (sulfuric) make an ether and
water.
An alcohol with an acid and heat will make an
alkene
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Electrophilic Addition
The acid attacks the pi bond breaking it an
leaving a carbocation.
The halogen attaches to the ion to make a
halide.
Also called hydrohalogenation.
Product can be determined using
Markalnikov’s rule.
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Hydrohalogenation
Hydrochoric and hydrobromic acids are hydrohalides
HCl, HBr
101
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Markovnikov’s rule
In the addition of HX to an alkene, the H
attaches to the carbon that already has the
most H’s, and the X attaches to the carbon
that has fewer H’s.
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Markonvnikov’s Rule
Only one product is produced because
of the mechanism of hydrohalogenation
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Reaction Mechanism
104
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Use Markovnikov’s rule to predict the product
for a hydration as well.
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Alkynes
It is important to note that all reactions that
occur with alkenes will occur in alkynes.
Each step in the mechanism just has to
happen twice.
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Biochemistry
The body uses complex catalysts to help with
these organic reactions, but the principles and
products are the same.
Ex. Alcohol in the body.
NAD+ is called a dehydrogenase (enzyme)
because it removes two hydrogens each time.
It is also the electron acceptor in the redox.
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Oxidation of Alcohols, Aldehydes,
Ketones and Carboxylic Acids
1˚ primary alchohol
2˚ primary alchohol
Aldehyde
Carboxylic Acid
Ketone
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Alkene Polymers
A polymer is a large molecule formed by the
repetitive bonding together of many smaller
molecules called monomers.
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Polymers
Because the monomer units in synthetic polymers
are all the same (except for copolymers), an
abbreviated formula can be used.
Monomer
Ethylene
H
H
C
C
H
-(CH2-CH2)-n
H
Vinyl chloride
H
Cl
C
H
Polymer
polyethylene
poly(vinyl chloride)
-(CH2-CH )-n
|
C
H
Cl
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Polymerization
Polymers are formed either by:
Chain polymerization
A multi-step process involving initiation,
propagation and termination. Polymer size
is relatively uniform.
Stepwise polymerization
A process where polymer size and amount
increase as a function of time.
Chain polymerization
Chain initiation
• This is the first step in chain polymerization.
• An initiator is added to form a radical
species which adds to a monomer.
• The resulting species is also a radical.
Rad
+ CH2
CHCl
Rad CH2 CHCl
Chain polymerization
Chain propagation
• The newly formed radical is then able to
react with another monomer unit.
• This process will continue, resulting in an
increasing longer chain.
Rad-CH2-CHCl + CH2 CHCl
Rad-CH2-CHCl -CH2-CHCl
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Chain polymerization
Chain termination
• This occurs when two radicals combine.
• Initially unlikely occurrence because much
more monomer than radical is present.
• As the monomer is depleted, termination
becomes much more likely.
Rad-CH2-CHCl -CH2-CHCl + Rad-CH2-CHCl -CH2-CHCl
Rad-CH2-CHCl -CH2-CHCl
CHCl-CH2-CHCl-CH2-Rad
Step polymerization
For step polymerization to occur, each
monomer unit must have two reactive groups.
Example. Preparation of nylon.
Adipoyl chloride
ClC(CH2)4CCl
||
||
O
O
hexamethylenediamine
+
H2N(CH2)6NH2
ClC(CH2)4C-NH(CH2)6NH2 + HCl
||
||
O
O
Step polymerization
ClC(CH2)4C-NH(CH2)6NH2
||
||
O
O
Product still has two reactive groups.
Polymer length is a function of time.
Polymer types
Fibers
These result when the intermolecular forces
between polymer molecules are strong.
Chains can be lined up by stretching.
HO
HO
O
HO
HO
O
HO
O
HO
O
HO
O
HO
O
HO
O
HO
O
Polymer types
Elastomers
In these polymers,
intermolecular
attractions are weak.
Crosslinking the
chains is one way of
helping them to
maintain a shape.
crosslink
Polymer types
Plastics
Somewhere between fibrous polymers and
elastomers.
Thermoplastic
Soften when heated
Example - polyethylene.
Thermoset plastic
Do not soften when heated.
These are typically highly crosslinked
polymers.
Polymers in the Body
Amino acids linking to make proteins.
DNA and RNA
In both cases the body uses enzymes to
assist in the creation to ensure the function
will be correct.
Skin and cell membranes are also polymers
of a sort (lipids)
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Aromatic Compounds
Compounds containing benzene-like rings.
Conjugated rings.
Benzene and other aromatic compounds are
much less reactive than alkenes.
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Structure of Benzene, C6H6
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Structure of Benzene, C6H6
Benzene is relatively stable
The ring system is preserved in reactions
All C-C bonds are identical.
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Structure of Benzene, C6H6
bond is an intermediate between a C-C and
C=C.
Simple aromatic hydrocarbons like benzene
are nonpolar, insoluble in water, volatile, and
flammable. (like alkanes)
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Naming Aromatic Compounds
Substituted benzenes are named using benzene as the parent.
No number is needed for monosubstituted
benzenes because all the ring positions are
identical.
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Phenyl and Benzyl Groups
CH2
Benzyl group
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Ortho, Meta and Para
Number the ring so have the smallest numbers
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Common Names
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Benzene
Benzene
phenol
Toluene
Cumene
Styrene
Toluene
cumene
benzaldehyde
Benzoic Acid
Phenol
Benzaldehy
de
Benzoic
acid
Styrene
aniline
Aniline
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Common Names
H
Benzene
CH3
Toluene
CH3
CH
CH3
Cumene
CH=CH2 Styrene
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Common Names
OH
Phenol
NH2
Aniline
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Common Names
CH=O
Benzaldehyde
CO2H
Benzoic Acid
CH2-
benzyl
Groups
O-
phenyl
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Reactions of Aromatic
Compounds
Unlike alkenes, which undergo addition
reactions, aromatic compounds usually
undergo substitution reactions.
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Reactions
Halogenation
FeCl3 →
Cl
Nitration
Chlorobenzene
HNO3
HONO2
H2SO4
→
NO2
Nitrobenzene
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Reactions
Friedel-Crafts Alkylation
AlCl3
R-Cl
CH2=H2
O
║
R-C-Cl
→
H2SO4
→
AlCl3
→
R
CH2CH3
O
║
CR
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Nitration is the substitution of a nitro group for
one of the ring hydrogens.
The reaction occurs when benzene reacts
with nitric acid in the presence of sulfuric
acid as catalyst:
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Halogenation is the substitution of a halogen
atom, usually bromine or chlorine, for one of
the ring hydrogens.
The reaction occurs when benzene reacts
with Br2 or Cl2 in the presence of iron as
catalyst:
Copyright ©
Chapter Thirteen
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