Chemistry 121(001) Winter 2015
Introduction to Organic Chemistry and Biochemistry
Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)
E-mail: upali@latech.edu
Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;
Office Hours: MTW 8:00 - 10:00 am;
ThF 9:00 - 10:00 am 1:00 - 2:00 pm.
December 19, 2014: Test 1 (Chapters 12-13)
January 26 , 2015: Test 2 (Chapters 14-16)
February 13, 2015: Test 3 (Chapters 17-19)
March 2, 2015:
Test 4 (Chapters 20-22)
March 3 , 2015: Make Up Exam: Chapters 12-22)
Bring Scantron Sheet 882-E
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GHW Questions
GHW#2
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Chapter 12. Saturated Hydrocarbons
12.1 Organic and Inorganic Compounds, 341
12.2 Bonding Characteristics of the Carbon Atom, 342
12.3 Hydrocarbons and Hydrocarbon Derivatives, 342
12.4 Alkanes: Acyclic Saturated Hydrocarbons, 343
12.5 Structural Formulas, 344
12.6 Alkane Isomerism, 346
12.7 Conformations of Alkanes, 348
12.8 IUPAC Nomenclature for Alkanes, 350
12.9 Line-Angle Structural Formulas for Alkanes, 356
12.10 Classification of Carbon Atoms, 358
12.11 Branched-Chain Alkyl Groups, 359
12.12 Cycloalkanes, 361
12.13 IUPAC Nomenclature for Cycloalkanes, 362
12.14 Isomerism in Cycloalkanes, 363
12.15 Sources of Alkanes and Cycloalkanes, 365
12.16 Physical Properties of Alkanes and Cycloalkanes, 367
12.17 Chemical Properties of Alkanes and Cycloalkanes, 368
12.18 Halogenated Alkanes and Cycloalkanes, 371
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Isomerism
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
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Constitutional Isomers
Skeletal (Chp. 12)
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
CH 3
CH 3
CH 3
H
CH 3
H
H
H
HH
HH
Enantiomers (Optical) (Chp. 16)
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CO 2H
C
H
OH
CH 3
CO 2H
C
HO
H
CH 3
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Constitutional isomers in butane
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
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CH3 CH2 CH2 CH3
CH3
CH3 CHCH3
Butane
(bp -0.5°C)
2-Meth ylp ropan e
(bp -11.6°C)
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Constitutional Isomers of Alkanes (CnH2n+2)
Number n of carbon Atoms
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1
2
3
4
5
6
7
8
9
10
11
12
13
Isomers of CnH2n+2
1
1
1
2
3
5
9
18
35
75
159
355
802
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1. Give the number of constitutional
isomers possible in following alkanes.
a) CH4
c) C3H8
e) C5H12
g) C7H16
i) C9H20
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_________
_________
_________
_________
b) C2H6
d) C4H10
f) C6H14
h) C8H18
_________
_________
_________
_________
_________
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2. Give the IUPAC name of the following
branched alkane:
CH3C(CH3)2CH2CH(CH2CH3)CH2CH3
a) Expanded condensed formula:
b) Line-angle formula:
c) Branched Alkyl groups and their names:
d) IUPAC name of the compound:
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Types of carbon atoms
Carbon atoms in alkanes and other organic compounds are classified
by the number of other carbons directly bonded to them.
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Types of carbon atoms
1.
2.
3.
4.
Primary (1◦) Carbon connected to one carbon atoms.
Secondary (2◦) Carbon connected to two carbon atoms.
Tertiary (3◦) Carbon connected to three carbon atoms.
How many primary, secondary, and tertiary carbons in the
two different structures of C4H10
H
H H H H
H C C C C H
H H H H
Butane, C 4H10
Primary = ?
Secondary =
Tertiary =
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H C H
H
H
H C C C H
H H H
Isobutane, C 4H10
Primary =
Secondary =
Tertiary =
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3. Identify the type of carbon atoms
in the following structure
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GHW#1: #9 IUPAC name of the following
branched alkane:
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Reactions of alkanes
Combustion
CH4(g) + 2O2(g)
CO2(g) + 2H2O(g)
Many alkanes are used this way - as fuels
– Methane
– Propane
– Butane
– Gasoline
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-
natural gas
used in gas grills
lighters
mixture of many hydrocarbons,
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Reactions of alkanes
Halogenation
– A reaction where a halogen replaces one or more
hydrogens.
heat or light
CH4(g) + Cl2(g)
CH3Cl(g) + HCl(g)
Used to prepare many solvents
• dichloromethane - paint stripper
• chloroform - once used as anesthesia
• 1,2-dichloroethane - dry cleaning fluid
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4. Complete combustion reaction
of following alkanes.
a) CH4
b) C4H10
c) C5H12
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Cycloalknes
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
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Cycloalkanes :saturated hydrocarbons
with a carbon ring
Have C-C single bonds in a ring structure.
General formula CnH2n
cyclopropane
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cyclobutane
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Naming 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.
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Cycloalkanes
Cycloalkanes have molecular formula CnH2n and contain carbon atoms arranged in a ring.
Simple cycloalkanes are named by adding the prefix cyclo- to the name of the acyclic
alkane having the same number of carbons.
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Naming simple of cycloalkanes:
cyclopropane
cyclobutane
cyclopentane
cyclohexane
cycloheptane
cyclooctane
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Ring strain in cycloalkane
The stability of cycloalkanes depends on their
ability to relieve ring strain when the bond angles
are less than 109.5˚.
60º
Least stable
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90º
108º
109.5º
Most stable
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Naming branched cycloalkanes
Commonly written as line-angle formulas
examples:
Isopropylcyclopentan e
1-tert -Bu tyl-4-methylcycloh exane
1-Isobutyl-2-meth ylcyclohexan e
1-Ethyl-1-methylcyclopropane
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5. IUPAC name of the following
substituted cycloakane
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Cis and trans Geometrical isomers of Cycloalkanes
•
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.
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Disubstituted Cycloalkanes
There are two different 1,2-dimethylcyclopentanes—one having two
CH3 groups on the same side of the ring and one having them on
opposite sides of the ring.
A and B are isomers. Specifically, they are stereoisomers.
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Haloalkanes
An alkane in which one or more H atoms is
replaced with a halogen (F, Cl, Br, or I)
CH3Br
1-bromomethane
(methyl bromide)
Br
CH3CH2CHCH3
2-bromobutane
Cl
chlorocyclobutane
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6. Give the common/IUPAC names of
following substituted alkanes:
Common
IUPAC
a) CH2Cl2
_________________
_________________
b) CHCl3
_________________
_________________
c) CCl3F
_________________
_________________
e) CCl2F2
_________________
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_________________
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7. Define following types of terms used
in describing isomerism:
a) Isomers: An example:
b) Constitutional isomers:
An example:
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Conformers of Alkanes
•Structures resulting from the free rotation of a
C-C single bond
•May differ in energy. The lowest-energy
conformer is most prevalent.
•Molecules constantly rotate through all the
possible conformations.
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Ethane Conformers
Staggered conformer has lowest energy.
Dihedral angle = 60 degrees
H
H
H
Dihedral angle
H
H
H
Newman
projection
sawhorse
model
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Ethane Conformers (2)
Eclipsed conformer has highest energy
Dihedral angle = 0 degrees
=>
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Conformational Analysis
•Torsional strain: resistance to rotation.
•For ethane, only 12.6 kJ/mol
eclipsed
staggered
=>
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Conformational Analysis Butane
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Conformational Analysis Butane
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Stereoisomers
c) Conformational stereroisomers:
d) Geometric stereoisomers:
e) Optical stereoisomers (d and l
Enantiomers):
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8) Describe the conformational
isomerism in following alknes:
a) Butane, C4H10:
b) Cyclopenatane, C5H10:
c) Cyclohexane C6H12:
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Units of Unsaturation
• Units of Unsaturation is the number of double
(p) bonds and/or rings in the molecule.
• Each ring or multiple bond replaces 2 H's in the alkane
formula CnH2n+2
• It relates molecular formula to possible structures
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9. Calculate the units of unsaturation in
following hydrocarbons
a) Butane, C4H10:
b) Cyclopenatane, C5H10:
c) Ethene (ethylene), C2H4:
d) Cyclohexa-1,3,5-triene (Benzene), C6H6:
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