chem1102 lecture notes 4-5
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1Chemistry 1102Charlie BondMCS Rm 4.16/4.27Charles.Bond@uwa.edu.au
What is Organic Chemistry?Organic Reactions I IIAlkanes (Ch 21)Conformational Analysis (Ch 21)Stereochemistry I II III (Ch 22)Alkyl Halides I II (Ch 24)Alcohols and Ether I II (Ch 24)
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2Problems to do in Brown&LeMay
21.1- 21.37 except 21.4, 21.15, 21.16 21.19, 21.20
Online self-help study at www.masteringchemistry.com
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3Organic Chemistry
H-C C-HH-C-C-HH
H
H
H HC C
H
H H
Hydrocarbons
Alkanes(Chapter3)
Alkenes(Chapters45)
Alkynes(Chapter4)
Arenes(Chapter9)
Onlycarboncarbonsingle
bonds
Oneormorecarboncarbondoublebonds
Oneormorecarboncarbontriplebonds
Oneormorebenzenelike
rings
Class
Example
Carboncarbonbonding
Name Ethane Ethylene Acetylene Benzene
Saturated Unsaturated
ethene ethyne
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4Structure
Hydrocarbon:Hydrocarbon: a compound composed only of carbon and hydrogen
Saturated hydrocarbon:Saturated hydrocarbon: a hydrocarbon containing only single bonds
Alkane:Alkane: a saturated hydrocarbon whose carbons are arranged in a open chain
Aliphatic hydrocarbon:Aliphatic hydrocarbon: another name for an alkane
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5Nomenclature Alkanes have the general formula CnH2n+2
names of unbranched chain alkanes
MolecularFormulaName
heptane
hexane
pentane
butane
propaneethanemethane CH4
C2H6C3H8C4H10C5H12C6H14C7H16
tetradecane
hexadecane
octadecane
eicosane
decanenonane
octane C8H18
C9H20C10H22
C14H30C16H34C18H38C20H42
dodecane C12H26
MolecularFormulaName
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6IUPAC Nomenclature Common alkyl groups
-CH2CH3
-CH3
-CH2CH2CH3-CHCH3CH3-CH2CH2CH2CH3
-CH2CHCH3CH3
-CHCH2CH3CH3
-CCH3CH3
CH3tertbutyl
secbutyl
isobutyl
butyl
isopropyl
propyl
ethylmethyl
NameCondensedStructuralFormula
CondensedStructuralFormulaName
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7IUPAC Nomenclature1.The name of an alkane with an unbranched chain
consists of a prefix and the suffix aneane2. For branched alkanes, the parent chain is the longest
chain of carbon atoms3. Each substituent is given a name and a number
4. If there is one substituent, number the chain from the end that gives it the lower number
CH3CH3CH2CH2CHCH32Methylpentane
14 3 2
5
CH3CHCH3CH3
2Methylpropane1
23
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8Classification of Carbons Primary (1):Primary (1): a C bonded to one other carbon Secondary (2):Secondary (2): a C bonded to two other carbons Tertiary (3):Tertiary (3): a C bonded to three other carbons Quaternary (4)Quaternary (4): a C bonded to four other carbons
a4carbon a3carbon
a2carbon
CH3-C-CH2-CH-CH3
2,2,4Trimethylpentane
CH3
CH3
CH3a1carbon a1carbon
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9Constitutional Isomers Constitutional isomers: compounds with the same
molecular formula but a different connectivity of their atoms there are two constitutional isomers with molecular
formula C4H10
CH3CH2CH2CH3 CH3CHCH3CH3
Butane(bp0.5C)
2Methylpropane(bp11.6C)
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10
Constitutional Isomerism the potential for constitutional isomerism is
enormous
4,111,846,763
4,3477531
ConstitutionalIsomers
MolecularFormula
CH4C5H12C10H22C15H32
C30H6236,797,588C25H52
World populationWorld populationisis
>6,000,000,000>6,000,000,000
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11
Physical Properties Alkanes are nonpolar compounds and have only
weak interactions between their molecules Dispersion forces:Dispersion forces: weak intermolecular forces of
attraction resulting from interaction of temporary induced dipoles
At Room Temperature:1-4C are gases (e.g. butane), 5-17C are liquids (e.g.
hexane, kerosene), 18+C are solids/waxes (e.g. parafin wax).
average density is about 0.7 g/mLliquid and solid alkanes float on water
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12
Physical Properties Constitutional isomers are different compounds and
have different physical propertiesMeltingPoint(C)
BoilingPoint(C)Name
hexane
2methylpentane3methylpentane
2,3dimethylbutane2,2dimethylbutane
69
6264
5850
Density(g/mL)
95
236
129100
0.659
0.6530.664
0.6620.649
Hexane
2,2Dimethylbutane
Melting point goes up with branching less flexibility, molecules can pack together more easilyBoiling point goes down with branching less available surface area for interactions (e.g. compare spaghetti with spaghetti hoops)
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13
Reactions of Alkanes Oxidation is the basis for the use of
alkanes as energy sources for heat and power heat of combustion:heat of combustion: heat released when
one mole of a substance is oxidized to carbon dioxide and water
CH4 2O2
CH3CH2CH3 5O2
CO2
3CO2
2H2O
4H2O
Methane++
++Propane
H=212kcal/mol
H=530kcal/mol
-886 kJ/mol
-2215 kJ/molC2H6 + 3.5O2 2CO2 + 3H2O Ho = -1427 kJ/mol
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14
Conformations of EthaneConformations of Ethane
Staggered Conformation
C C
H HH H
H HEthane
H
HH
H
H
H
Newman projection
60
Each carbon-hydrogen bond bisects the angle between two carbon-hydrogen bonds on the other carbon
Each hydrogen on the front carbon is perfectly staggered between two hydrogens on the back carbon
ConformationConformation: any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond
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15
Conformations of EthaneConformations of Ethane Eclipsed Conformation
Each carbon-hydrogen bond on one carbon of the eclipsed conformation of ethane is directly in line with a carbon-hydrogen
bond on the other carbon The back carbon-hydrogen bonds lie directly behind the front
carbon-hydrogen bonds The front hydrogens eclipse the back hydrogens
C C
H HH H
H HEthane
H
HH
H
H H
Newman projection
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16
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17
Conformations of ButaneConformations of Butane
C C
C C
H HH H
Butane
H HH H
H H1
2 3
4
Conformation analysis about C2-C3 bond of butane is more complex, because each carbon has a methyl group and two hydrogens bonded to it
HH
C
C
H H
C
H H
C
H H
H H
HHH H
HH
H
H
HH
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18
Conformations of ButaneConformations of Butane
CH3
HH
H
H3C
H
staggered conformer
H3CH
H
H
CH3
H
eclipsed conformer
H3C
H
H
H
CH3
H
staggered conformer
CH3
HHH
CH3
H
eclipsed conformer
C C
H3C CH3
H HH H
12 3
4
C C
H3C
CH3
HH
12 3
4
HH
Newman projectionsNewman projections
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19
Conformations of ButaneConformations of Butane Staggered Conformations
The methyl groups are said to be anti if the angle between them is 180
Is the most stable because is staggered and has the two methyl groups as far apart as possible
CH3
HH
H
H3C
H
conformer 1
H3C
H
H
H
CH3
H
conformer 2
We can predict that conformer 1 will be of lower energy than alternative staggered conformer 2
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20
Conformations of ButaneConformations of Butane Eclipsed Conformations
The eclipsed conformation is 19 kJ/mol higher in energy than anti, due to a H with H and CH3 with CH3 eclipsing interactions
CH3
HH H
H3C
H
conformer 1
conformer 2
H3CH
H
H
CH3
H
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21
The energy difference between the low-energy staggered anti conformer and the highest energy eclipsed conformer is about 19 kJ/mol
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22
Physical Properties Constitutional isomers are different compounds and
have different physical propertiesMeltingPoint(C)
BoilingPoint(C)Name
hexane
2methylpentane3methylpentane
2,3dimethylbutane2,2dimethylbutane
69
6264
5850
Density(g/mL)
95
236
129100
0.659
0.6530.664
0.6620.649
Hexane
2,2Dimethylbutane
Melting point goes up with branching less flexibility, molecules can pack together more easilyBoiling point goes down with branching less available surface area for interactions (e.g. compare spaghetti with spaghetti hoops)
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23
Cycloalkanes General formula CCnnHH2n2n
five- and six-membered rings are the most common
Cyclopentane, cyclohexane
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24
Cyclic Molecules in NatureCyclic Molecules in Nature
Steroids are an important class of compounds occurring in all animals and plants and have many important functions;
hormones, anabolic steroids
OH
H HHH H H
OCH3
HO OEstradiol Progesterone
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25
Conformations of CyclohexaneConformations of Cyclohexane This is a chair conformation The view along C1 C5 shows that there
are no eclipsing C H
All bonds are fully staggered, giving the lowest energy possible
This is why cyclohexane is strain free
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26
Conformations of CyclohexaneConformations of Cyclohexane
Staggered Conformation of Butane
C C
C C
H HH H
Butane
H HH H
H H1
2 3
4
This is a chair conformation of cyclohexane
H3C
H
H
H
CH3
H
conformer 2
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27
Conformations of CyclohexaneConformations of Cyclohexane This is a boat conformation Now all the C H bonds are eclipsed
Boat conformation is 25 kJ/mol
higher in energy than chair conformation
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28
Conformations of CyclohexaneConformations of Cyclohexane
CH3
HH H
H3C
H
Newman projection
C C
C C
H HH H
Butane
H HH H
H H1
2 3
4
Eclipsed Conformation of Butane
This is a boat conformation of cyclohexane
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29
Eclipsed conformation of butane
Conformations of CyclohexaneConformations of Cyclohexane
CH3
HH
H
H3C
H
Newman projection
CH3
HH H
H3C
H
Newman projection
Staggered conformation of butane
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30
Drawing CyclohexaneDrawing Cyclohexane1. Draw two parallel lines, slanted
downward and slightly offset from each other. This means that four of the cyclohexane carbon atoms lie in plane.
3. Locate the top most carbon above and to the right of the plane of the other four atoms and connect the bonds.
5. Locate the bottom most carbon atom below and to the left of the plane of the middle four and connect the bonds.
7. Note that the bonds to the bottom most carbon are parallel to the bonds to the top most carbon.
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31
Drawing CyclohexaneDrawing Cyclohexane1. Start off with one end. Locate
the top carbon on the left.
2. Next draw the two parallel lines of equal lengths. At this stage,
the top of the new line should be level with the top of the original pair.
6. Finally, the last lines should be parallel to the first pair of lines
shown, and the lowest points should also be level.
these lines should be parallel
these lines should be parallel
Level
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32
How How Not Not to Draw Cyclohexaneto Draw Cyclohexane
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33
AxialAxial and and EquatorialEquatorial Bonds in Cyclohexane Bonds in Cyclohexane The chair conformation has two kinds of positions for substituents
on the ring: axial positions and equatorial positions Chair cyclohexane has six axial hydrogens perpendicular to the
ring (parallel to the ring axis) and six equatorial hydrogens near the plane of the ring
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34
AxialAxial and and Equatorial Equatorial BondsBonds
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35
Conformational Mobility of Cyclohexane Conformational Mobility of Cyclohexane
The chair conformations readily interconvert, resulting in the exchange of axial and equatorial positions by a ring-flip
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36
Ring flippingRing flippingFor an animation, look athttp://www.chem.calgary.ca/courses/351/Carey5th/Ch03/ch3-06.html
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37
NH
N
OO
OHOH
OHHOH2C
OHHO
H NH
Tetrodotoxin
The Poisonous PufferfishThe Poisonous Pufferfish
25 milligrams of tetrodotoxin would be expected to kill a 75 kg person
FuguFugu- is the Japanese word for pufferfish and is also a Japanese dish prepared from the meat of pufferfish."I want to eat fugu, but I don't want to die" "I want to eat fugu, but I don't want to die" Fugu wa kuitashii, inochi wa oshishii
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38
Conformation of Methylcyclohexane Conformation of Methylcyclohexane CH3
The two conformers of methylcyclohexane are not equal in energy
HHH3C
HH
H
123
4 561
234
5 6
chairequatorial 95%
chairaxial 5%
boat
CH3
H
H
HH
H
H
H
CH3
HH
H
H
HH
H
H
H
H
H
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39
The equatorial conformer of methyl cyclohexane is more stable than the axial conformer by 7.6 kJ/mol
Conformation of Methylcyclohexane Conformation of Methylcyclohexane
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40
CH3
Cl CH3Cl
CH3
Cl
I II III
CH3
IV
Cl
Problem:Problem: Which of the following cyclohexanes has the highest highest energy?
Problem:Problem: Which of the following cyclohexanes has the lowestlowest energy?
C
Cl
I II III IV
H3C
CH3
CH3C
CCH3CH3H3C
Cl
H3CCH3
CH3Cl
CCH3CH3H3CCl
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41
Conformations of CyclohexaneConformations of Cyclohexane
H
H
1
234
5 6
H
HH
H
H
HH
H
H
H
these H atoms are allup relative to their partnerson the same C carbon
these H atoms are alldown relative to their partnerson the same C carbon
H H
OH OH
HOH
H
e
a
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42
What happens with more than one substituent on the cyclohexane ring? Problem:Problem: Draw the conformations of the two isomers of cis and trans 1,2-cyclohexanediol.
OH
H
both OH groups occupy positions on the upper side of the ring
cis - 1,2-cyclohexanediol both H atoms occupy positions on the lower side of the ring
e
a e aOH
OH OH
H
OH
HHO
H1
22 1
OH
Hea e
aH
OH
H
OHHO
H1
22 1
conformer with bothOH axial
the more stableconformer with bothOH equatorial
trans - 1,2-cyclohexanediol
OH
OH
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43
Problem:Problem: Draw the conformations of the two isomers of cis and trans 1,4-cyclohexanediol.
OH OH
HOH
HOH OH
H
H
HO
conformer with bothOH axial
the more stableconformer with bothOH equatorial
trans - 1,4-cyclohexanediol
a
a
ee
OH H
OHH
OHOH OH
H
H
HO
both H atoms occupy positions on the upper side of the ring
cis - 1,4-cyclohexanediol both OH groups occupy positions on the lower side of the ring
e
a
e
a
1
4
4
1
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44
Draw the preferred conformations of the two isomers of 1,3,5-trimethylcyclohexane
CH3CH3
CH3
H
H
H
axialequatorial
13
5
axialequatorial
13
5CH3
HCH3
H
H3C
H
1
3
5
1
3
5
CH3
H
H
CH3
H3C
H 13
5
CH3
H
H3C
H
H3C
H 13
5
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