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Physical Properties of Organic
Compounds Alkanes
Melting and boiling points increase with increasingmolecular weight within a homologous series.
Compound Formula MW(g/mol)
mp (C) bp (C)
Methane CH4 16 182 164
Pentane CH3(CH2)3CH3 72 130 36
Decane CH3(CH2)8CH3 142 30 174
Pentadecane CH3(CH2)13CH3 212 10 271
Eicosane CH3(CH2)18CH3 282 37 343
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Physical Properties of Organic
Compounds
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Physical Properties of Organic
Compounds
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Physical Properties of Organic
Compounds Alkanes
Boiling points decrease with chain branching.
Compoundbp
(oC)
mp
(oC)
CH3CH3
CH3 CH3
CH3
CH3 CH3
CH3 CH3
CH3
octane
4-methylheptane
2,2,4-trimethylpentane
57
121
107
127
118
99
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Physical Properties of Organic
Compounds
Alkanes
Solubility Like dissolves like
Alkanes are nonpolar, hydrophobicThey are soluble in nonpolar solvents
and insoluble in water.
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Physical Properties of Organic
Compounds
CH3
CH3
Compound MW p
(oC)
H2O
solubilit
6. 6 insolubl
ClCl . 6 3 0. %
CH3CH3
O
O
86.09 88 20%
x ne
1,2-di loroet ne
2,3-but nedione
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Physical Properties of Organic
Compounds
CH3O
OCH3
HOOH
H2NNH2
CH3N
NCH3
H
H
Compound MWbp
(oC)
H2O
solubilit
90.12 83
90.12 230
88.15 158
88.15 119
dimet ox et ne
1, -but nediol
putres ine
N,N'-dimet let lenedi mine
g
g
g
g
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Physical Properties of Organic
Compounds
Which of the following has the highest
boiling point?
CH3CH2 CH
CH3
CH3 CH3CH2 CH
NH2
CH3 CH3CH2 CH
OH
CH3
CH3CH2 CH
Cl
CH3 CH3CH2 CH
CH2CH3
CH3
1. 2. 3.
4. 5.
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Physical Properties of Organic
Compounds
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Physical Properties of Organic
Compounds
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Isomerism
Isomerism The phenomenonwhereby certain chemical compoundshave structures that are different
although the compounds possess thesame elemental composition.
Isomers Two or more chemicalsubstances having the same elementary
composition and molecular weight butdiffering in structure.
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Consider C4H10
H
CH C
H
H
C
H
H
C
H
H
H
HC C
C
C
H
H
H HH
H
H H
H H
Normal Butane Isobutane
Isomerism
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ISOMERS
CONFIGURATIONALOPTICALSTRUCTURAL CONFORMATIONAL
SkeletalFunctionalPositionalTautomers
Compounds w/ samemolecular formula butw/ structures that aremirror image of theother
Rotate plane ofpolarized light equallybut in opposite direction
Enantiomers chiral,non-superimposablemirror images
Diastereomers non-superimposable, non-mirror imagesAnomersEpimers - different ingeometry
Samestereochemicalconfiguration butdiffering in 3Dconformation
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ConstitutionalIsomers-skeletal
C4H10
C5H12
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ConstitutionalIsomers-skeletal
C6H14 ?
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ConstitutionalIsomers-skeletal
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ConstitutionalIsomers-skeletal
H
O
H
O
OHOH
O
O
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ConstitutionalIsomers-positional
OH
OH
HO OHHO
OH
O
O
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ConstitutionalIsomers-functional
OH O
H
O O
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ConformationalIsomers
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ConformationalIsomers
=
H
H H
H H
H
St ggered
U = 60o
U
=
H
H H
H
H
H
Ecli
U
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ConformationalIsomers
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ConformationalIsomers
U
Erel
180o
0 kcal/mol
120o
3.4 kc al/mol
60o
0.9 kcal/mol
0o
6.1 kcal/mol
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Which is the most stable conformation for 1-
chloropropane about the C1-C2 bond?
ClH
H
CH3
H H
HH
Cl
CH3
H H
HCl
H
CH3
H H
Cl
H H
CH3
H H
H
H Cl
CH3
H H
1. 2. 3.
4. 5.
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