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CH1810 Lecture #4
Organic Chemistry Basics
Carbon and The Scope of Organic Chemistry
The Position of Carbon in the Periodic TableThe Position of Carbon in the Periodic Table
Organic Chemistry - General Description
A. The Study of Carbon Compounds
B. “Organic” reminds us of plant or animal origins 1. “Natural” medicines: morphine, penicillin 2. “Natural” fibers: cotton, silk, wool 3. Foodstuffs: Fats, carbohydrates, proteins, vitamins 4. “Natural” rubber
C. Man-made substances can also be “organic” 1. Drugs: xylocaine, aspirin, acetaminophen 2. Fibers: nylon, dacron, rayon 3. Polymers: Saran wrap, polyesters, teflon, nylon 4. Synthetic rubber, synfuels
Differences Between Organic and Inorganic Compounds
Inorganic OrganicElements Present Metals and Nometals Mostly Carbon
Bonding Covalent and Ionic Mostly Covalent
“Particles” IONS & molecules ions & MOLECULES
Melting Points Relatively High Relatively LowBoiling Points Relatively High Relatively Low
Electrolytes STRONG to weak weak to NON
Comparison of Physical Properties of Organic and Inorganic Compounds
Name Salt Ethyl alcohol Benzene
Formula NaCl C2H6O C6H6
Organic/Inorganic Inorganic Organic Organic
Melting Point 804 ºC -117 ºC 5 ºC
Boiling Point 1413 ºC 78 ºC 80 ºC
Burns in O2 ? No Yes Yes
Water Soluble ? Yes Yes No
Structural Representation of Simple Alkanes
Review of Valence Bond Theory
Carbon Bonding in Alkanes
Carbon atoms in alkanes have the following characteristics:
Carbon is tetravalent: each carbon has four bonds; The four bonds possess tetrahedral geometry; The four bonds are equivalent and have similar properties.
The angle between any two bonds of a tetrahedral carbon in any carbon compound is 109.5o, the tetrahedral bond angle.
Carbon: ground-state electron configuration
2p
2s
1s
2p
2s
1s
Carbon: excited-state electron configuration
Carbon:
sp3-hybridized electron configuration
2sp3
1s
}hybridization
excitationEn
erg
yThe sp3 Hybridization Scheme for Carbon
The sp3 Hybridization Scheme
excitation
hybridization
an s and 3 p orbitals combine
4 sp3 hybrid orbitals
which are represented as
C
The Hybrid Orbital Picture of Methane
CH4
C
4 carbon sp3 hybrid orbitals
4 hydrogen 1s atomic orbitals
Methane
Ethane, CH3CH3The sp3 hybrid orbitals of
two carbons overlap
The remaining sp3 hybrid orbitals overlap with hydrogen s orbitals
7 sigma bonds
Carbon: ground-state electron configuration
2p
2s
1s
2p
2s
1s
Carbon: excited-state electron configuration
Carbon:
sp2-hybridized electron configuration
2p
2sp2
1s
}hybridization
excitation
En
erg
yThe sp2 Hybridization Scheme for Carbon
2p 2sp2
1s
An sp2-hybridized Carbon
The sp2 hybrid orbitals of two carbons overlap
The remaining sp2 hybrid orbitals overlap with hydrogen s orbitals
Ethene, CH2CH2
5 sigma bonds
The remaining unhybridized p orbitals overlap to form a ∏ bond.
∏ bond contains 2 electrons.
5 sigma bonds and 1 ∏ bond
Ethene, CH2CH2
Carbon: ground-state electron configuration
2p
2s
1s
2p
2s
1s
Carbon: excited-state electron configuration
Carbon:
sp2-hybridized electron configuration
2p
2sp2
1s
}hybridization
excitation
En
erg
yThe sp Hybridization Scheme for Carbon
2p 2sp2
1s
An sp2-hybridized Carbon
The sp hybrid orbitals of two carbons overlap
The remaining sp hybrid orbitals overlap with hydrogen s orbitals
Ethyne, CHCH
3 sigma bonds
The remaining unhybridized p orbitals overlap to form 2 ∏ bonds.
3 sigma bonds and 2 ∏ bonds
Each ∏ bond contains 2 electrons.
Bonding in HCCHH C C H
H
C
C
H
Structural Formulas and Bond Angles
120º
180º
Methane (109.5º angles)Ethane (109º angles)
CC
H
H
H
HH
H 109.5º
109.5º
“Sigma” and “Pi” Bonds
𝝈 π
7 sigma bonds
5 sigma bonds and 1 ∏ bond
3 sigma bonds and 2 ∏ bonds
C CH
HH
HH
H
C CH
H
H
H
C CH H
ethane
ethene
ethyne
Occupied “bonding” orbitals
Alkanes Aldehydes
Alkenes Ketones
Alkynes Carboxylic Acids
Aromatics Esters
Alcohols Amines
Ethers Amides
Families of Organic Compounds
C C
C C
C C
CC
CC
C
C
C O
H
C OC
CH
O
CC
O
C
CO
H
O
C
O
OC
N
CN
O
Alkanes
Hydrocarbons The Simplest Class of Organic Compounds
C. Hydrocarbons are further subclassified
C C C C C
UNSATURATED
ALIPHATIC AROMATIC
SATURATED
alkanes alkenes alkynes aromatics
Unsaturated hydrocarbons – alkenes or alkynes that can combine with H2 to form alkanes in a process called
CC
CCCC
HH
H
H H
H + 3 H2 C C C
CCC
H H
H
H
H
H
H
H
H
H
H
H
Benzene Cyclohexane
catalytic surface
catalytic surface
catalytic surface
CH4
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH3
CH3CH2CH2CH3
CH3CH2CH3
CH3CH3
Formulas and Properties of “Normal” Alkanes
Homologous Series
Members of the series
differ by one —CH2— group
CH4
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH3
CH3CH2CH2CH3
CH3CH2CH3
CH3CH3
Formulas and Properties of “Normal” Alkanesn Molecular Condensed Name Melting Boiling
Formula Structural Formula point (oC) point (oC)
1 CH4 methane -182 -1622 C2H6 ethane -183 -893 C3H8 propane -190 -424 C4H10 butane -138 -15 C5H12 pentane -130 366 C6H14 hexane -95 697 C7H16 heptane -91 988 C8H18 octane -57 1269 C9H20 nonane -51 151
10 C10H22 decane -30 174
Boiling Points of the First Ten Alkanes
All Molecules
Polar Molecules
Molecules containing O-H, N-H, or F-H
Bonds
Dispersion forces
Dipole forces
H-bonding
Hierarchy of Intermolecular Forces
Boiling Points of Straight Chain Alkanes NonPolar Molecules
Effect of Molecular Shapeon Size of Dispersion Force
n-pentane molar mass=72.15
b.p = 36.1 ºC
2-methylbutane molar mass=72.15
b.p = 27.9 ºC
2,2-dimethylpropane molar mass=72.15
b.p = 9.5 ºC
A larger surface-to-surface contact between molecules results in stronger dispersion force attractions and a
higher boiling point.
Drawing Organic Molecules
Lewis Structure
Condensed Structure
Carbon-Skeleton Structure
Molecular Formula C5H12
Alkanes - The Meaning of Line Structures
A. Atoms may freely “rotate” about Single bonds
B. Such rotation is not evident in very simple molecules, but can be demonstrated in models of larger molecules
1. Methane - CH4
Rotation does not change the spacial relationship between hydrogen atoms.
2. Ethane - CH3CH3
Rotation does change the spatial relationship between hydrogen atoms
“Conformations” of Alkanes
Conformations of Alkanes
C. CONFORMATIONS - Different arrangements of atoms in a molecule which can be interconverted by rotation about single bonds
D. In a given sample of a compound, the molecules usually exist as a mixture of conformations. One or two conformations are usually the most stable.
E. Though they may appear different on paper, different conformers represent the same molecule
CH3 CH2 CH2 CH3 CH2 CH2 CH3
CH3
CH3
CH2 CH2
CH3 CH3
CH2 CH2
CH3
CH3 CH2
CH3
CH2
Rotation about a bond is not isomerism.
Isomerism, A Complicating Factor in Organic Chemistry
A. A molecular formula may not convey a unique structure.
B. Isomers - Compounds with identical molecular formulas, but different structural formulas.
C. Example #1: C4H10
Compound
Name Butane Isobutane
Melting point -138 oC -160 oC
Boiling point 0 oC -12 oC
Density 0.601 g/mL 0.557 g/mL
H3CCH2 CH2
CH3
H
CH3C CH3
CH3
Isomerism
Isomerism
n-butane iso-butanebutane 2-methylpropane
Alkane Nomenclature
Alkane Nomenclature
Why is the IUPAC system Necessary ?
Consider the following “carbon hydrides”
CH4 C2H6 C2H4 C2H2
Each formula represents a unique compound.
When structural formulas are considered, however,
C3H7 has only 1 isomer. C4H10 has 2 isomers.
C5H12 has 3 isomers. C6H14 has 5 isomers.
C10H22 has 75 isomers. C30H62 has 4 x 109 isomers.
Basis of the IUPAC System of naming-The Root Name
The root name of a compound is derived from the longest continuous chain of carbon atoms
or the longest continuous chain of carbon atoms containing a given
special structural feature.
1) Common stems are used to indicate the length of carbon chains.
meth-, eth-, pro-, but-, pent-, hex-, hept-, oct-, non-, dec-
2) Common suffixes are use to indicate the class of compounds.
Alkane Alkene Alkyne
C CC CC C
Alkane Nomenclature
“Substituents” may be attached to a carbon chain
1. Substituents which are not pieces of alkanes
2. Substituents which are pieces of alkanes: “Alkyl” groups
Alkane Nomenclature
1. Substituents which are not pieces of alkanes:
-F “Fluoro”- -NO2 “Nitro”-
-Cl “Chloro"- -NH2 “Amino”-
-Br “Bromo”- -OH “Hydroxy”-
-I “Iodo”-
Alkane Nomenclature
2. Substituents which are pieces of alkanes - “Alkyl” groups
Names are derived from the parent alkanes.
C HH
H
H
Parent alkane When attached to another chain
Methane
CH
H
H
Parent Chain
Methyl- BASE NAME
C CH
H
H
H
H
H
Ethane
C CH
H
H
H
H
Parent Chain
Ethyl- BASE NAME
Alkane Nomenclature
2. Substituents which are pieces of alkanes - “Alkyl” groups
Parent alkane When attached to another chain
C CH
H
H
H
H
H
Parent Chain
Propane Propyl- BASE NAME
C
H
H C CH
H
H
H
H
H
C
H
C CH
H
H
H H
C
H
H
Parent Chain Isopropyl- BASE NAME
Alkane Nomenclature
methyl- CH3-
ethyl- CH3CH2-
propyl- CH3CH2CH2-
isopropyl- (CH3)2CH-
n-butyl- CH3CH2CH2CH2-
s-butyl- CH3CH2CHCH3
isobutyl- (CH3)2CH2CH-
t-butyl- (CH3)3CH-
Alkane Nomenclature -Alkyl GroupsName Formula Line structure
C3H7-
C4H9-
C2H5-
CH3-
Alkane Nomenclature -Final Step
Position of Attachment of Substituents is Indicated
1. For carbon chains with double or triple bonds (alkenes and alkynes), the numbering system for the base carbon chain has already been established and does not change.
2. For saturated carbon chains (alkanes) the numbering system for the base carbon chain is determined by the positions of the substituents.
Substituent names (in alphabetical order) and numbers are added (prefixed) to the base name of the compound.
Putting it Together for a Simple Alkane
CH3 CH2 CH2 CH
CH CH3
CH3
CH CH3
CH2
CH3
7 6 5 4 3
2
1
Family
heptane
Longest chain
Base name
Alkyl groups
methylisopropyl
Position of alkyl groups
4- -3-
CH3 CH2 CH2 CH
CH CH3
CH3
CH CH3
CH2
CH3
Alkane Nomenclature Worksheet
Br
1) 2)
3)4)
2-methyl pentane
2,3-dimethyl pentane
2,3,4-trimethyl hexane1-bromo-3,3-dimethyl pentane
H3CCH
CH2CH2
CH3
CH3
H3CCH
CHCH2
CH3
CH3
CH3
3,4-dimethyl hexane
BrCl
5) 2,2,3,3,4,4-hexamethyl pentane
6)
7) 2,2,3-trimethylnonane
8) 3,3-diethyl-4-isopropylheptane
1 1
35
1
5
18
14
1 8
Cycloalkanes
C
C C
H H
H
H
H
H
CC
CC
C
C
H HH
H
H
HH H
HH
H
H
1. Structures are usually abbreviated
2. Planar representations do not represent 3-D shape.
Nomenclature - Cyclic Alkanes
3. Cyclic structures are numbered and named to give the lowest numbers to substituents.
Nomenclature - Cyclic Alkanes
CH3H3C1,2-dimethylcyclopentane 1,2,4-trimethylcyclohexane
CH3
H3C
H3C1 2
1
2 34
1 1
35
9) 10)
1-isopropyl-3-methyl cyclohexane
1,1,3,3-tetramethyl cyclopentane
1
3
1 3
BrCl
Question: Are pentane and cyclopentane isomers ???
C5H12 C5H10