Organic Chemistry I
University of Lincoln
presentation
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Organic chemistry
C is a small atom
It forms single, double, and triple bonds
It is intermediate in electronegativity (2.5)
It forms strong covalent bonds with C, H, O, N, S and
some metals
What’s so important about Carbon Chemistry?
>7 or 10 or 30! million Organic Compounds (depends on the source)
1.5 million Inorganic Compounds
Lubricants, Cosmetics, Fragrances, Pigments, Dyes, Inks, Adhesives, Explosives,
Detergents, Surfactants, Emulsifiers, Coolants, Photographic agents, Forensic
chemicals, Plastics, Drugs, ….
And most important!! Is the base of the Chemistry of Life
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Carbon has 4 valence electrons
H
H
H C H
H
Ne
Methane
Neon
x
H
C
H
H
Methane
x
x
x
Stable Octet required
Covalent bonding – Atoms share electrons
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Problem
bonding by 2s and 2p atomic orbitals would give bond angles of
approximately 90°.
Instead we observe bond angles of approximately 109.5°, 120°, and
180°
Solution
hybridization of atomic orbitals
2nd row elements use sp3, sp2, and sp hybrid orbitals for bonding
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C(6) – 1s2, 2s2, 2px1, 2py1, 2pz0
Lowest energy state
C(6) – 1s2, 2s1, 2px1, 2py1, 2pz1
Excited state
4 sp3
2s
+
+
+
2py
2px
2pz
4 x sp3
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Hybridization of orbitals
(L. Pauling)
“The combination of two or more atomic orbitals forms a
new set of atomic orbitals, called hybrid orbitals”
We deal with three types of hybrid orbitals
sp3 (one s orbital + three p orbitals)
sp2 (one s orbital + two p orbitals)
sp (one s orbital + one p orbital)
Overlap of hybrid orbitals can form two types of bonds
depending on the geometry of overlap
σ bonds are formed by “direct” overlap
π bonds are formed by “parallel” overlap
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sp3 Hybrid Orbitals
– each sp3 hybrid orbital
has two lobes of unequal
size
– the sign of the wave
function is positive in one
lobe, negative in the
other, and zero at the
nucleus
– the four sp3 hybrid
orbitals are directed
toward the corners of a
regular tetrahedron at
angles of 109.5°
H
H
H
H
109.5o
An sp3 orbital
Four
tetrahedral
sp3 orbitals
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Methane is Tetrahedral
Sigma bonds
formed by
overlap of sp3
and 1s orbitals
H
H
H
H
109.5o
H
H
H
H
Methane
Sp3 hybridized carbon
4 equivalent C-H bonds (s-bonds)
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sp 2Hybrid Orbitals
– the axes of the three sp2 hybrid orbitals lie in a plane
and are directed toward the corners of an equilateral
triangle
– the unhybridized 2p orbital lies perpendicular to the
plane of the three hybrid orbitals
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H
H
H
H
Bonding in Ethylene
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sp Hybrid Orbitals
Two lobes of unequal size at an angle of 180°
The unhybridized 2p orbitals are perpendicular to each other
and to the line created by the axes of the two sp hybrid orbitals
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Bond
Orbital overlap
Orbital
Predicted Types of
Hybridis Bond
Bonds to
ation
Angles
Carbon
C-C
sp3-sp3
sp3
C-H
sp3-1s
C-C
sp2-sp2, 2p-2p
sp2-1s
C-C
sp-sp, two 2p-2p
sp-1s
4 sigma
bonds
H
sp2
sp
120o
180o
3 sigma bonds
and 1 pi bond
2 sigma
bonds and 2
pi bonds
Name
Ethane
H
H
H
H
C-H
C-H
109.5o
Example
H
Ethylene
H
H
H
H
Acetylene
H
H
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Aldehydes
Halocarbons
Alcohols
Ketones
Hydrocarbons
Nitriles
Ethers
Organic Compounds
Nitrocompounds
Acids
Amines
Esters
Amides
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HYDROCARBONS
contain only C and H atoms
ALIPHATIC
hydrocarbons
SATURATED
hydrocarbons
contain C–C and C–H
single bonds only (ALKANES)
ALKENE
contains the
C=C functional group
AROMATIC
Hydrocarbons must contain a
BENZENE ring
UNSATURATED
hydrocarbons
contain at least 1
C–C multiple bond
ALKYNE
contains the
C≡C functional group
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Alkanes
• Chemical formula CnH2n+2
n = 1, 2, 3, …
• CH4, methane, simplest
one
• C2H6, ethane
• All have –ane ending
– Follow a pattern
Prefix
Number
Meth-
One
Eth-
Two
Prop-
Three
But-
Four
Pent-
Five
Hex-
Six
Hept-
Seven
Oct-
Eight
Non-
Nine
Dec-
Ten
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Properties of Alkanes
Name
Molecular
formula
Melting point
(oC)
Boiling point
(oC)
Density at
20oC (g/mL)
Methane
CH4
-183
-162
(Gas)
Ethane
C2H6
-172
-89
(Gas)
Propane
C3H8
-188
-42
(Gas)
Butane
C4H10
-138
0
(Gas)
Pentane
C5H12
-130
36
0.626
Hexane
C6H14
-95
69
0.659
Heptane
C7H16
-91
98
0.684
Octane
C8H18
-57
126
0.703
Decane
C10H22
-30
174
0.730
Dodecane
C12H26
-10
216
0.749
Tetradecane
C14H30
6
254
0.763
Hexadecane
C16H34
18
280
0.775
Octadecane
C18H38
28
316
(Solid)
Eicosane
C20H42
37
343
(Solid)
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Cycloalkanes
• Carbon atom chains
in form of rings
• Name: cyclo + alkane
name (i.e.
Cyclobutane)
Cycloalkanes have
higher bpt/mpt
than straight chain
alkanes with the
same number of
carbon atoms
Cyclopropane
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Isomerism
• Isomers: compounds with same
molecular formula but
different structural formulas
• Differences in structure may
give rise to differences in
chemical and physical
properties
• To name them choose the
longest unbroken chain, and
number the alkyl groups to
obtain the lowest possible
number (2, methylpropane)
Butane
Isobutane
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C4H10 – has two isomers, n-butane
and isobutane (2-methylpropane)
H
CH3
H3C
CH3
Isobutane
2, methylbutane
Has the same molecular
formula as n-pentane, C5H12
2, 2 dimethylpropane
CH3
CH3
H3C
Isopentane
H3C
They all have different Physical
Properties, Mpt, Bpt, densities
CH3
H3C
CH3
Neopentane
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Reactions of Alkanes
■ Combustion
CH4  2O2  CO2  2H2O  energy
■ Dehydrogenation
R
R
High temp
Cataly st
+
R
H
H
R
alkene
■ Halogenation
H
H
H
H
H
H
H
Ethane
+
H
Heat or light
Br Br
H
Br
H
+
HBr
H
Bromoethane
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IUPAC rules
CH3
4
2
H3C
CH3
3
5
1
2-methylpentane (not 4-methylpentane)
CH3
1
2
5
3
H3C
CH3
4
The ending –ane means the C-C bonds are
single. The Pent- tells us the longest chain
is 5 carbons. They are numbered starting
closest to the branch point.
This is a saturated 6 carbon long chain with
a methyl group attached to the third
carbon.
6
3-methylhexane (not 2-ethylpentane or 4-methylhexane)
CH3
H3C
1
3
2
CH3
CH3
Each addition to the carbon chain has its
own number. The prefix di- inditcated
there are two additional methyl groups.
4
2,2-dimethylbutane (not 2,2-methylbutane or 2dimethylbutane)
2
Cl
1
Br
3
CH3
4
3-bromo-1-chlorobutane (not 1-chloro-3-bromobutane or
2-bromo-4-chlorobutane)
The carbon chain is numbered from the
end closest to the first additonal group. The
additional groups are then named in
alphabetical order irrespective of position
number.
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Alkane
Alkyl group
Methane
Methyl (CH3-)
Ethane
Ethyl (CH3CH2-)
Propane
Propyl (CH3CH2CH2-)
Butane
Methyl
(CH3CH2CH2CH2-)
CH3
H3C
2
4
3
2-Methylbutane
CH3
1
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Alkenes
• Alkene: Unsaturated hydrocarbon that
contains one or more carbon-to-carbon
double bonds
CH3
– General formula of CnH2n
H2C
• All have –ene ending
• Simplest: ethylene, C2H4
CH2
3, methyl-1,4-pentadiene
CH3
CH2
H2C
H2C
1,3-Butadiene
1-Butene
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Reactions of Alkenes
H
H
■ Addition reactions
+
H
H
H
H
H
X
H
H
OH
H
Alkyl Halides
Alkyl hydrogen Sulphate
Alcohols
H
H
X
X
H
X
H
H
H
H
H
A
H
H
OSO 3 H
H
H
H
H
H
X-X
X
H
H
H - OSO3H
H - OH
A
H
H
H-X
H
Dihaloalkanes
H
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■ Hydrogenation (another addition reaction)
H
H
+
H
H
H
H
Pt or Pd Catalyst
H
solvent, pressure
H
H
H
H
H
Pt
ethanol, 1atm
C 2H4  3O2  2CO2  2H2 O
Cyclohexene
Cyclohexane
■ Oxidation
KMnO4, -OH, H2O
H2C
CH2
■ Combustion
OH
HO
+
MnO2
C 2H4  3O2  2CO2  2H2 O
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H
H
■ Polymerisation
H
H
Polymers are large molecules
containing many identical
repeating units (100-1000000)
Addition polymer is a polymer
in which the monomer simply
add together with no other
products formed besides
polymer
H
H
H
H
H
H
CH3
n
H
CH3
H
H
H
H
Cl
polypropylene
propylene
Cl
n
H
H
H
H
polyethylene
ethylene
H
Polymerisation reaction is a
repetition reaction which
combines many small molecules
of monomer (alkene) to form a
polymer
n
H
n
H
H
H
H
H
F
F
n
vinyl chloride poly(vinylchloride), PVC
F
F
F
n
F
F
H
H
Styrene
n
F
n
teflon
tetrafluoroethene
H
H
H
H
H
H
H
H
n
polystyrene
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Alkynes
• Alkyne: hydrocarbon that
contains one or more
carbon-to-carbon triple
bonds
• General formula of CnH2n–2
• All have –yne ending
• Simplest: acetylene, C2H2
H
H
Acetylene
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Reactions of Alkynes
■ Combustion
Alkynes are high energy compounds
+
H
H
2.5 O2
+
2 CO2
H2O
Welding gas
■ Addition reactions
H
H
H
H
H
+
+
H
X
X
H
H
H
H
X
X
H
X
H
O
H
H
+
O3
H X
X
then H2O
OH
H
H
+
+
H
X
E xc es s
H
H X
H
H
H
H
H
HO
O
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Acknowledgements
•
•
•
•
•
•
•
JISC
HEA
Centre for Educational Research and Development
School of natural and applied sciences
School of Journalism
SirenFM
http://tango.freedesktop.org
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