ch2210 an introduction to organic chemistry -...
TRANSCRIPT
CH2210 An Introduction
to Organic Chemistry
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 Formulas and Condensed Structures
Because organic compounds are molecular in nature, the additional information conveyed in structural formulas is sometimes necessary.
Structural formulas show the connections between atoms based on their abilities to form covalent bonds.
HC
C
C
O
O
N
N
N
F
Cl
Br
Main-Group Elements have common bonding patterns
Because certain carbon and hydrogen groupings are so common, some abbreviations are used.
Structural Formulas and Condensed Structures
C
H
H
H CH3 C
H
H
CH2
C
H
CH CH2CH2 (CH2)2
Structural Formulas and Condensed Structures
C
C
C C C
H
H C
C
C C C C O
H
H HH
H
H H
H
HH
H
H
H
H
H
H
H
H H
H
H3C
CH
H3C
CH
HC CH
CH3
(CH2)4 OH
Example of a Condensed Structure: What does the molecular formula C11H22O represent ?
Structural Formulas and Condensed Structures
Abbreviations for Cyclic StructuresCH2
H2C
H2CCH2
CH2
CH2
CH2H2C
H2CCH2
CH
CH
CH2
CH2
CH2
CH2
C
C
CC
C
CH
H
H
H
H
H
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
Alcohols Phenols Ethers Thiols Dissulfides Amines
-O- -S- -N-
OC
Alkanes Alkenes Alkynes Aromatics
Aldehydes Ketones Acids Esters Anhydrides Amides
OC-N
OC-O
Hydrocarbons
All Classes of Organic Compounds
Functionalized Hydrocarbons
Halides
F,Cl,Br O,S,N
OC
C C C C C
C
C
C
C C C C C C C
C
C C
CCC
C
C
CC
C
CC
CC
CC
C
CC
C
CC
C
C
CC
CC
Bonding Patterns of Carbon
Linear ChainBranched Chain
Cube
Simple Rings Fused Rings
Allotropes of Carbon
Hydrocarbons The Simplest Class of Organic Compounds
Hydrocarbons The Simplest Class of Organic Compounds
A. Contain only Carbon and Hydrogen B. Carbon can bond in different ways
C
H
HH
H
C
H
HH
H
CH4
180º120º
VSEPR Model
120º
180º180º
C C
H
H H
H
C C H H
Hydrocarbons The Simplest Class of Organic Compounds
B. Carbon can bond in different ways (multiple bonds)
C CH H
C CH
H H
H
Hydrocarbons The Simplest Class of Organic Compounds
C. Hydrocarbons are further subclassified
C C C C C
UNSATURATED
ALIPHATIC AROMATIC
SATURATED
Structural Formulas and Bond Angles
120º
180º
Methane (109.5º angles)
Structural Representation of Simple Alkanes
Alkanes - The Meaning of Line Structure
CH4
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH3
CH3CH2CH2CH3
CH3CH2CH3
CH3CH3
Formulas and Properties of “Normal” Alkanes
Homologous Series
n 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
CH4
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH3
CH3CH2CH2CH3
CH3CH2CH3
CH3CH3
Formulas and Properties of “Normal” Alkanes
Uses of Hydrocarbons
Supplement on
Hybridization
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
excitation
En
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
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
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
A molecular formula may not convey a unique structure.
Isomers - Compounds with identical molecular formulas, but different structural formulas.
Isomerism
n-butane iso-butanebutane 2-methylpropane
Compound
Name Acetic Acid Methyl formate
Melting point 16.6 oC -99 oC
Boiling point 118 oC 31 oC
Density 1.05 g/mL 0.97 g/mL
H3CC
O
OH
HC
O
OCH3
Isomerism Example #2: C2H4O2
Compounds with the Formula C4H10O
H3CCH2
CH2CH2
OH CH3
CH2CH2
OCH3
CH3CHCH2
OH
CH3
CH3CH2
OCH2
CH3
CH3CH2
CHCH3
O
H
CH3CH
OCH3
CH3
CH3C
OH
CH3H3C
Compounds with the Formula C4H8O
H3CCH2
C
O
CH3H3C
CHC
O
H
CH3
OH2C
H2C CH2
CH2 O
H2C CH2
HC
CH3
O
CH2
C
CH3
CH3
H2C
H2C CH2
HC
O
H
C C
CH2CH2
O
H
H
H
H
Isomerism Two Compounds
The compounds cannot be isomers.
Are the chemical formulas the same ?NoYes
The compounds are constitutional isomers. Are the compounds superimposable ?
Yes
No
The compounds are stereoisomers.
The compounds are identical.
The compounds are enantiomers.
The compounds are diastereomers.
Are the connectivities of the atoms the same ?
Yes No
Are the compounds mirror images?
NoYes
Isomer Worksheet
H3C
CH
H3C
CH2 CH2 CH3
CH3 CH2
CH2 CH
CH3
CH3
1)
2) CH3 CH2
CH2 CH
CH3
CH3
CH3 CH2 CH CH2 CH3
CH3
3)
4)
C6H14 C6H14
C6H14C6H14
C6H14 C6H14
C6H14C5H12
identical
isomers
isomers
unrelated
5)
6)
7)
8)
Cl Cl
CH3
H3C CH
CH3
OH
H3C CH2 CH2 OH
H3C CH2 C
O
CH3
O
H3C CH2 CH2 C
O
HH2C CH CH2 O CH3
C6H11Cl C6H11Clisomers
C3H8O C3H8Oisomers
C4H8O C4H8Oisomers
C4H8O C4H8Oisomers
Isomerism What is the relationship between these two
molecules?
2,3-dimethylpentane 2,3-dimethylhexane
C7H16 C8H18
Isomerism What is the relationship between these two
molecules?
and
2,4-dimethylpentane 2,2-dimethylpentane
C7H16 C7H16
Isomerism What is the relationship between these two
molecules?
2,3-dimethylpentane 2,3-dimethylpentane
C7H16 C7H16
Supplement on
Hybridization
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.