Chemistry 121(01) Winter 2010-11
Introduction to Organic Chemistry and Biochemistry
Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)
E-mail: [email protected]
Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;
Office Hours: MWF 8:00 am - 10:00 am;
TT 9:00 – 10:00 am & 1:00-2:00 pm.
December 17, 2010 Test 1 (Chapters 12-13)
January 19, 2011 Test 2 (Chapters 14,15 & 16)
February 7, 2011 Test 3(Chapters 17, 18 & 19)
February 23, 2011 Test 4 (Chapters 20, 21 & 22)
February 24, 2011
Comprehensive Make Up Exam:
Chemistry 121, Winter 2009-10, LA Tech
Sections 12.4-12.14 & 12.6
12-1
Alkanes: Acyclic Saturated Hydrocarbons
Alkane Isomerism
Conformations of Alkanes
IUPAC Nomenclature for Alkanes
Classification of Carbon Atoms
Branched-Chain Alkyl Groups
Cycloalkanes
IUPAC Nomenclature for Cycloalkanes
Isomerism in Cycloalkanes
Sources of Alkanes and Cycloalkanes
Physical Properties of Alkanes and Cycloalkanes
Chemical Properties of Alkanes and Cycloalkanes
Nomenclature and Properties of Halogenated Alkanes
Chemical Connections: Chlorofluorocarbons and the
Ozone Layer
Chemistry 121, Winter 2009-10, LA Tech
12-2
Chemistry 121, Winter 2009-10, LA Tech
Organic vs Inorganic Compounds
Chapter 12. Saturated Hydrocarbons
12.4
12.6
12.7
12.8
12.10
12.11
12.12
12.13
12.14
12.15
12.16
12.17
12.18
Chapter 12. Saturated Hydrocarbons
12-3
← Fig. 12.1
Sheer numbers is one
reason why organic
chemistry is a
separate field of
chemical study.
Chemistry 121, Winter 2009-10, LA Tech
12-4
1
Classification of Hydrocarbons
Types of formula for organic compounds
Fig. 12.2 Terms for organic compounds.
Chemical formula: Indicate the kind and number of each
type of atom in the molecule.
Condensed formula: Shows skeletal atoms in a molecule
and places them in a sequential order that indicates
bonding.
Structural formula: Shows each atom and bonds in a
molecule.
Line-angle formula: The hydrogen atoms are removed from
carbon chains, leaving just a carbon line skeleton with
functional groups attached to it.
Chemistry 121, Winter 2009-10, LA Tech
12-5
Alicyclic Alkanes
Chemistry 121, Winter 2009-10, LA Tech
12-6
Models of Hydrocarbons
← Fig. 12.3
Are saturated hydrocarbons:
•Noncyclic alkanes: General molecular formula, CnH2n+2
Molecular structures of (a) methane, (b) ethane, and (c) propane, the
three simplest alkanes.
Structural formula:
Chemistry 121, Winter 2009-10, LA Tech
12-7
Chemistry 121, Winter 2009-10, LA Tech
12-8
2
Physical Properties of Hydrocarbons
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.
Fig. 12.4
Models of (a) pentane, (b) isopentane, and (c) neopentane.
Chemistry 121, Winter 2009-10, LA Tech
12-9
Naming alkanes
Nomenclature: Unbranched or straight chain alkanes
1 Find the longest carbon chain.
Use as base name with an ane ending.
2 Locate any branches on chain.
Use base names with a yl ending.
3 For multiple branch of the same type,
modify name with di, tri, ...
4 Show the location of each branch with
numbers.
5 List multiple branches alphabetically
- the di, tri, ... don’t count..
General molecular formula: CnH2n+2
All bond angles about tetrahedral carbon are approximately 109.5°
12-11
Molecular
Formula
N ame
Molecular
Formula
methane CH4
nonane
C9 H2 0
ethan e
C2 H6
propane C H
3 8
decan e
C1 0 H2 2
dodecan e
C1 2 H2 6
tetrad ecane
C1 4 H3 0
N ame
bu tane
C4 H1 0
pen tane C5 H1 2
hexan e
C6 H1 4
hep tane C7 H1 6
octane
Chemistry 121, Winter 2009-10, LA Tech
12-10
Chemistry 121, Winter 2009-10, LA Tech
Chemistry 121, Winter 2009-10, LA Tech
hexadecane C1 6 H3 4
octadecan e
C1 8 H3 8
eicosane
C2 0 H4 2
C8 H1 8
12-12
3
Alkanes
Names of Alkyl Groups
First four members of the alkanes
Name
Methane
# of C
1
methyl
ethyl
propyl
isopropyl
butyl
sec-butyl
isobutyl
tert-butyl
Condensed formula
CH4
Ethane
2
CH3CH3
Propane
3
CH3CH2CH3
Butane
4
CH3CH2CH2CH3
Called a homologous series
“Members differ by number of CH2 groups”
12-13
Chemistry 121, Winter 2009-10, LA Tech
H4 methane: CH3- methyl
CH3CH3 ethane: CH3CH2- ethyl
CH3CH2CH2(CH3)2CHCH3CH2CH2CH2CH3CH2 (CH3) CH(CH3)2CHCH2(CH3)3C-
12-14
Chemistry 121, Winter 2009-10, LA Tech
Constitutional isomers in butane
Constitutional isomers
Compounds with the same number and type of atoms
but with different arrangements.
Molecular Formula
C5H12
Constitutional isomers: compounds with the same
molecular formula but a different connectivity of their
atoms in the skeleton.
There are two constitutional isomers with molecular
formula C4H10
Condensed structural formulas.
CH3CH2CH2CH2CH3
CH3CH(CH3)CH2CH3
(CH3)4C
pentane
2-methylbutane
2,2-dimethylpropane
All are constitutional isomers of C5H12.
Chemistry 121, Winter 2009-10, LA Tech
12-15
CH3 CH2 CH2 CH3
CH3
CH3 CHCH3
Butane
(bp -0.5°C)
2-Meth ylp ropan e
(bp -11.6°C)
Chemistry 121, Winter 2009-10, LA Tech
12-16
4
Molecular Structure and Physical Properties
Alkanes
•Bp decreases with hydrocarbon chain branching due to decrease
in surface area which results in fewer intermolecular attractions.
Physical Properties
• Mp increases with hydrocarbon chain branching because the
more compact molecules have a better fit in the crystal lattice
making it more stable.
• Nonpolar molecules
• Not soluble in water
•Solubility - the quantity of solute that will dissolve in a solvent
depends on polarity of solute and solvent.
“Like dissolves like” refers to polar liquids tending to dissolve
polar solutes and nonpolar liquids tend to dissolve nonpolar
solutes. Alkanes are nonpolar.
12-17
Chemistry 121, Winter 2009-10, LA Tech
Chemistry 121, Winter 2009-10, LA Tech
bp, oC
-161.7
- 88.6
- 42.2
-0.5
36.1
68.7
98.4
125.6
150.7
174.0
mp, oC
-182.6
-182.8
-187.1
-135.0
-129.7
- 94.0
- 90.5
- 56.8
-53.7
-29.7
• Low density
• Low melting point
• Low boiling point
12-18
Chemistry 121, Winter 2009-10, LA Tech
Physical Properties of The Saturated Hydrocarbons
Physical Properties of Alkanes
Name
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
These go up
as the number
of carbons
increases.
Density at 20 oC
0.000667
0.00125
0.00183
0.00242
0.626
0.659
0.684
0.703
0.718
0.730
12-19
Name
Molecular
Formula
Melting
Point (oC)
Boiling
Point (oC)
State
at 25oC
methane
CH4
-182.5
-164
gas
ethane
C2H6
-183.3
-88.6
gas
propane
C3H8
-189.7
-42.1
gas
butane
C4H10
-138.4
-0.5
gas
pentane
C5H12
-129.7
36.1
liquid
hexane
C6H14
-95
68.9
liquid
heptane
C7H16
-90.6
98.4
liquid
octane
C8H18
-56.8
124.7
liquid
nonane
C9H20
-51
150.8
liquid
decane
C10H22
-29.7
174.1
liquid
eicosane
C20H42
36.8
343
Chemistry 121, Winter 2009-10, LA Tech
solid
12-20
5
Refining Crude Oil
Sources of Alkanes
→ Fig. 12.9 The complex hydrocarbon mixture present in petroleum
is separated into simpler mixtures by means of a fractionating
column.
Natural gas
90-95% methane, 5-10% ethane
Petroleum
•
•
•
•
•
•
gases (bp below 20°C)
naphthas, including gasoline (bp 20 - 200°C)
kerosene (bp 175 - 275°C)
fuel oil (bp 250 - 400°C)
lubricating oils (bp above 350°C)
asphalt (residue after distillation)
Coal
Chemistry 121, Winter 2009-10, LA Tech
12-21
Rules of IUPAC Nomenclature of Branched Alkanes
Parent name: the longest carbon chain
Substituent: a group bonded to the parent chain
Alkyl group: a substituent derived by removal of a
hydrogen from an alkane; given the symbol Rwritten in alphabetical order
CH4 becomes CH3- (methyl)
CH3CH3 becomes CH3CH2- (ethyl)
Prefixes: di-, tri-, tetra-, etc. are not included
in alphabetization
Chemistry 121, Winter 2009-10, LA Tech
12-23
12-22
Chemistry 121, Winter 2009-10, LA Tech
IUPAC Nomenclature of branched alkanes
• suffix -ane specifies an alkane
• prefix tells the number of carbon atoms
Prefix Carbons
meth1
eth 2
prop3
but4
pent5
hex6
hept7
oct8
non 9
dec10
Chemistry 121, Winter 2009-10, LA Tech
Carb on s
Prefix
undec11
dod ec12
tridec13
tetradec14
pentadec- 15
hexadec16
heptadec- 17
octad ec18
non adec19
eicos 20
12-24
6
Alkyl groups and their IUPAC names
Example
Fig. 12.5 The four most common branched-chain alkyl groups and their
IUPAC names.
Name the following.
(CH 3)2CHCH2CH2CH(CH3)2
This is a condensed structural formula.
First convert it to a carbon skeleton, leaving
out the hydrogen.
12-25
Chemistry 121, Winter 2009-10, LA Tech
12-26
Chemistry 121, Winter 2009-10, LA Tech
Common alkyl groups
N ame
methyl
Con dens ed
Structu ral Formula
-CH3
ethyl
-CH2 CH3
propyl
-CH2 CH2 CH3
isopropyl -CHCH3
CH3
bu tyl
-CH2 CH2 CH2 CH3
N ame
isobu tyl
sec-butyl
Con dens ed
Structu ral Formula
-CH2 CHCH3
CH3
(CH 3)2CHCH2CH2CH(CH3)2
-CHCH2 CH3
CH3
C
C
|
|
C-C-C-C-C-C
CH3
t ert-bu tyl -CCH3
CH3
Now name it!
Chemistry 121, Winter 2009-10, LA Tech
12-27
Chemistry 121, Winter 2009-10, LA Tech
12-28
7
Giving IUPAC names
• CH3CH2CH2CH(CH3)CH2CH2CH2CH3
Parent name: octane
C
C
|
|
C-C-C-C-C-C
subs tituent
parent chain
Substituent: Methyl at 4
4-mehtyl
1
Name: 4-Methyloctane
1. Longest chain is 6 - hexane
2
3
4
5
6
8
7
4-Methyloctane
CH3C(CH3)2CH2CH(CH2CH3)CH2CH3
2. Two methyl groups - dimethyl
CH3 CH2 CH3
3. Use 2,5-dimethylhexane
CH3 CCH2 CHCH2 CH3
CH3
1
2
3
4
6
5
4-Ethyl-2,2-dimeth ylh exane
12-29
Chemistry 121, Winter 2009-10, LA Tech
12-30
Chemistry 121, Winter 2009-10, LA Tech
Physical State of Saturated Hydrocarbons
Types of carbon and hydrogen atoms
Primary (1°) carbon: a C bonded to one other carbon
Secondary (2°) carbon :
a C bonded to two other carbons
Tertiary (3°) carbon :
a C bonded to three other carbons
Quaternary (4°) carbon :
a C bonded to four other carbons
a 2° carb on
a 4° carb on
a 3° carb on
CH3
CH3 -C-CH2 -CH-CH3
a 1° carb on
a 1° carb on
CH3
CH3
← Fig. 12.12
A physical-state
summary for
unbranched alkanes and
unsubstituted
cycloalkanes at room
temperature and
pressure.
2,2,4-Trimeth ylp entane
Primary (1°) hydrogen:
Secondary (2°) hydrogen :
Tertiary (3°) hydrogen :
Chemistry 121, Winter 2009-10, LA Tech
a H bonded to primary (1°) carbon
a H bonded to secondary (2°) carbon
a H bonded to tertiary (3°) carbon
12-31
Chemistry 121, Winter 2009-10, LA Tech
12-32
8
Reactions of 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
12-33
Chemistry 121, Winter 2009-10, LA Tech
Reactions of Alkanes
heat of combustion: heat released when one mole
of a substance is oxidized to carbon dioxide and
water in a combustion reaction.
CH3 CH2 CH3 + 5O2
Propane
CO2 + 2 H2 O
CH4(g) + 2O2(g)
Many alkanes are used this way - as fuels
•
•
•
•
Methane
Propane
Butane
Gasoline
-
natural gas
used in gas grills
lighters
mixture of many hydrocarbons,
12-34
Chemistry 121, Winter 2009-10, LA Tech
H° = -212 kcal/mol
A mixture of carbon monoxide and hydrogen in varying
proportions, depending on how it is produced
C + H2 O
Coal
CH4 + 1 O2
2
Methan e
CO + 2 H2
3CO2 + 4H2 O H° = -530 kcal/mol
12-35
heat
catalyst
CO + H2
CO + 2 H2
Methanol and acetic acid are produced from synthesis gas
CH3 OH + CO
Methan ol
Chemistry 121, Winter 2009-10, LA Tech
CO2(g) + 2H2O(g)
Synthesis Gas
Oxidation is the basis for the use of alkanes as
energy sources for heat and power
CH4 + 2O2
Methane
Combustion
Chemistry 121, Winter 2009-10, LA Tech
catalyst
catalyst
CH3 OH
Methan ol
O
CH3 COH
Acetic acid
12-36
9
Cycloalknes
Cycloalkanes
Cyclic alkanes: General molecular formula, CnH2n
Structure and nomenclature
• named similar to noncyclic alkanes
• to name, prefix the name of the corresponding open-chain alkane
with cyclo-, and name each substituent on the ring
• if only one substituent, no need to give it a number
• if two substituents, number from the substituent of lower
alphabetical order
• if three or more substituents, number to give them the lowest set
of numbers, and then list substituents in alphabetical order
• in planar cyclopentane, all C-C-C bond angles are 108°, which
differ only slightly from the tetrahedral angle of
109.5°consequently there is little angle strain
Fig. 12.6 Simple cycloalkanes
12-37
Chemistry 121, Winter 2009-10, LA Tech
Properties of Hydrocarbons cont’d
Chemistry 121, Winter 2009-10, LA Tech
12-38
Melting Points of Hydrocarbons
CAG 12.1
→ Fig. 12.11
For a series of
alkanes or
cycloalkanes, melting
point increases as
carbon chain length
increases.
Chemistry 121, Winter 2009-10, LA Tech
12-39
Chemistry 121, Winter 2009-10, LA Tech
12-40
10
Naming simple of cycloalkanes:
Ring strain in cycloalkane
cyclopropane
The stability of cycloalkanes depends on their
ability to relieve ring strain when the bond angles
are less than 109.5˚.
cyclobutane
cyclopentane
cyclohexane
60º
90º
108º
cycloheptane
109.5º
Most stable
Least stable
cyclooctane
12-41
Chemistry 121, Winter 2009-10, LA Tech
Naming branched cycloalkanes
Commonly written as line-angle formulas
12-42
Chemistry 121, Winter 2009-10, LA Tech
Cycloalkanes :saturated hydrocarbons with a carbon ring
examples:
Have C-C single bonds in a ring structure.
General formula CnH2n
Isopropylcyclopentan e
1-tert -Bu tyl-4-methylcycloh exane
1-Isobutyl-2-meth ylcyclohexan e
1-Ethyl-1-methylcyclopropane
cyclopropane
Chemistry 121, Winter 2009-10, LA Tech
12-43
Chemistry 121, Winter 2009-10, LA Tech
cyclobutane
12-44
11
Naming Cycloalkanes
Conformations of Cycloalkanes
Have the carbons connected in a ring. These
compounds are known collectively as
To name a cycloalkane, use the prefix cyclo- with
the parent. If there is only one substituent, a
number is not needed.
Cyclohexane
Chair conformation-low energy
Boat conformation-higher energy
Chemistry 121, Winter 2009-10, LA Tech
12-45
Geometrical (cis & trans) Isomers of
Cycloalkanes
12-46
Cis and trans Geometrical isomers of
Cycloalkanes
Carbon ring create a rigid structure
trans and cis is used to describe the
arrangements of alkyl groups with respect
to the plane of the ring
cis: on the same side
trans: on the opposite sides
Chemistry 121, Winter 2009-10, LA Tech
Chemistry 121, Winter 2009-10, LA Tech
12-47
two groups are said to be located cis to each other if
they lie on the same side of a plane.
If they are on opposite sides, their relative position is
described as trans.
Chemistry 121, Winter 2009-10, LA Tech
12-48
12
Conformations of cyclopentane
Boat conformations of cyclohexane
• In planar cyclopentane, there are 10 fully eclipsed C-H
bonds, which create torsional strain of approximately
10 kcal/mol
• Puckering to an “envelope” conformation relieves part
of this strain
• In an envelope conformation, eclipsed interactions are
reduced but angle strain is increased slightly (105°)
Planar conformation
Chemistry 121, Winter 2009-10, LA Tech
Envelope conformation
12-49
A puckered conformation in which carbons 1 and 4 are bent
toward each other
• a boat conformation is less stable than a chair conformation by 6.5
kcal (27 kJ)/mol
• torsional strain is created by four sets of eclipsed hydrogen
interactions
• steric strain (nonbonded interaction strain) is created by one set
of flagpole interactions
Chemistry 121, Winter 2009-10, LA Tech
12-50
Interconversions of conformations
Interconvert ion to alternative chair conformations (lower
energy) via a boat conformation (higher energy
Geometric isomerism: A stereoisomer concerning the
orientation differences of atoms or groups around a
double bond or ring
cis isomer - a geometric isomer where groups are on
the same side of a ring or double bond
flip th is
end dow n
trans isomer - a geometric isomer where groups are
on opposite sides of a ring or double bond
flip th is
end up
Chemistry 121, Winter 2009-10, LA Tech
Cis and Trans Geometric Isomerism in Cycloalkanes
12-51
Chemistry 121, Winter 2009-10, LA Tech
12-52
13
CH 3
cis-1,2-dimethylcyclopentane
CH 3
Problem: draw the alternative chair conformations of
this trisubstituted cyclohexane and state which is the
more stable
CH 3
trans-1,2-dimethylcyclopentane
H3 C
CH 3
cis-1,4-dimethylcyclohexane,
equ atorial
H
CH3
H
axial
CH3
Perspective drawing
H
CH3
CH3
H
H
H
CH3
H
axial
CH3
cis-1,4-D imethylcycloh exane
(th ese conformation s are of equ al stability)
Chemistry 121, Winter 2009-10, LA Tech
12-53
Chemistry 121, Winter 2009-10, LA Tech
12-54
CFCs and Ozone Depletion
Substitution Reactions of Alkanes
→ Fig. 12.14 In an alkane substitute reaction, an incoming molecule.
atom or group of atoms replaces a hydrogen atom in the alkane
 CC 12. 3
Chemistry 121, Winter 2009-10, LA Tech
12-55
Chemistry 121, Winter 2009-10, LA Tech
12-56
14
Halo-Alkanes
Saturated Hydrocarbons Derivatives
Fig. 12.15 Models of four ethyl halides.
Table 12.4
Chemistry 121, Winter 2009-10, LA Tech
12-57
Isomerism
Constitutional Isomers
Skeletal (Chp. 12)
Isomers - different compounds having the same molecular
formula but different structural formulas
There are two type of Isomers:
Constitutional isomerism: Different connections among
atoms in the
• Skeleton
• Position
• Functional group
Stereoisomerism: Same connectivity among atoms, but
these atoms differ in spatial orientation
• geometric
• conformational
• optical
Chemistry 121, Winter 2009-10, LA Tech
12-58
Chemistry 121, Winter 2009-10, LA Tech
12-59
CH 3
CH 3CH 2CH 2CH 3
CH 3CHCH 3
Functional (Chp. 14)
Positional (Chp. 12)
CH 3CH 2OH CH 3OCH 3
CH 3CH 2CH 2 CH 3CH CH 3
Br
Br
Stereoisomers
Geometric (Chp. 13) Conformational (Chp.12)
H
H
C C
Br
Br
H
Br
C C
Br
H
H
H
CH 3
CH 3
CH 3
CH 3
H
H
HH
HH
Enantiomers (Optical) (Chp. 16)
H
Chemistry 121, Winter 2009-10, LA Tech
CO 2H
C
OH
CH 3
HO
CO 2H
C
H
CH 3
12-60
15
Physical Properties Constitutional isomers
Constitutional isomerism in alkane
The number of constitutional isomerism increases with
the carbon number in the alkane
Mole cular
Formula
CH 4
Constitutional isomers are different compounds and
have different physical properties
Constitutional
Is ome rs
C5 H1 2
1
3
C1 0 H2 2
75
C1 5 H3 2
4,347
N ame
hexan e
3-methylp entane
2-methylp entane
Meltin g Boiling
Point Point D en sity
(°C)
(°C) (g/mL)
-95
69
0.659
64
62
58
0.664
0.653
0.662
50
0.649
C2 5 H5 2
36,797,588
-6
-23
2,3-dimethylbutan e -129
C3 0 H6 2
4,111,846,763
2,2-dimethylbutan e -100
Chemistry 121, Winter 2009-10, LA Tech
Hexane
2,2-Dimethylbutane
12-61
Chemistry 121, Winter 2009-10, LA Tech
12-62
16