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Roldan M. de Guia
Department of Biochemistry
Faculty of Pharmacy
University of Santo Tomas
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Physical Properties of OrganicCompounds
Alkanes Melting and boiling points increase with increasing
molecular weight within a homologous series.
Compound Formula MW(g/mol)
mp (C) bp (C)
Methane CH4
16 18 164
Pentane CH!"CH
#
!CH
!$ 1!% !6
Decane CH!"CH
#
8CH
!14 !% 1$4
Pentadecane CH!"CH
#
1!CH
!1 1% $1
Eicosane CH!"CH
#
18CH
!8 !$ !4!
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Physical Properties of OrganicCompounds
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Physical Properties of OrganicCompounds
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Physical Properties of OrganicCompounds
Alkanes &oiling 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
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Physical Properties of OrganicCompounds
Alkanes
'olubilit( )*ike dissol+es like,
Alkanes are nonpolar- h(drophobiche( are soluble in nonpolar sol+ents
and insoluble in water.
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Physical Properties of OrganicCompounds
CH3
CH3
Compound !"bp
(oC)
H2#
$olubility
8%&18 % in$oluble
ClCl 8&% 83 0&8'
CH3CH3
#
#
8%&0 88 20'
heane
1,2-dichloroethane
2,3-butanedione
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Physical Properties of OrganicCompounds
CH3#
#CH3
H##H
H2H2
CH3
CH3
H
H
Compound !" bp(oC)
H2#$olubility
0&12 83
0&12 230
88&15 158
88&15 11
dimethoyethane
1,4-butanediol
putre$cine
,*-dimethylethylenediamine
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Physical Properties of OrganicCompounds
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 OrganicCompounds
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Isomerism
Isomerism he phenomenonwhereb( certain chemical compoundsha+e structures that are di//erentalthough the compounds possess the
same elemental composition.
Isomers wo or more chemicalsubstances ha+ing the same elementar(
composition and molecular weight butdi//ering in structure.
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Consider C4H1%
H
CH CH
H
CH
H
CH
H
HH
C C
C
C
H
H
H HH
H
H HH H
0ormal &utane sobutane
Isomerism
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ISME!S
C"FI#$!%&I"%'P&IC%'S&!$C&$!%'C"F!M%&I"%'
SeletalFunctionalPositional&automers
Compounds w2 samemolecular /ormula butw2 structures that aremirror image o/ theother3otate plane o/polaried light e5uall(but in opposite direction
Enantiomers chiral-nonsuperimposablemirror imagesDiastereomers nonsuperimposable- nonmirror images%nomersEpimers
di//erent ingeometr(
'amestereochemicalcon/iguration butdi//ering in !7con/ormation
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Constitutional Isomers-skeletal
C4H10
C5H12
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Constitutional Isomers-skeletal
CH14 +
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Constitutional Isomers-skeletal
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Constitutional Isomers-skeletal
H
O
H
O
OH OH
O
O
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Constitutional Isomers-positional
OH
OH
HO OH HO
OH
O
O
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Constitutional Isomers-functional
OH O
H
O O
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Conformational Isomers
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Conformational Isomers
H
H H
H H
H
ta..ered %0o
H
H H
H
HH
/clip$ed
0o
f i l
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Conformational Isomers
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Conformational Isomers
Erel
180o
0 calmol
120o
3&4 calmol
%0o
0& calmol
0o
%&1 calmol
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Which is the most stable conformation for 1-
chloropropane abot the C1-C2 bon!?
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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!ing Conformers
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!ing Conformers
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!ing Conformers
H H
H
H
H
H
H H
H
H
H
H
Cyclohe"ane
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Cyclohe"ane !ing Conformers
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Cyclohe"ane !ing Conformers
HH
H
H
H H
H
H H
H
HH
%&
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Cyclohe"ane !ing Conformers
HH
H
H
H H
H
H H
H
HH
"tericinteractions
%&
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Cyclohe"ane !ing Conformers
HH
H
H
H H
H
H H
H
HH
#clipsing
%&
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Cyclohe"ane !ing Conformers
H
H
H
H
H
H
HH
H
H
H
H
C*%I!
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Cyclohe"ane !ing Conformers
#$atorial
h%!rogensH
H
H
H
H
H
HH
H
H
H
H
C*%I!
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Cyclohe"ane !ing Conformers
&'ial
h%!rogensH
H
H
H
H
H
HH
H
H
H
H
C*%I!
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Cyclohe"ane !ing Conformers
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Cyclohe"ane !ing Conformers
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Cyclohe"ane !ing Conformers
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Cyclohe"ane !ing Conformers
tert
&ut(lc(cloheane
se(ere steric
interactions
mch more stable
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#eometric Isomerisms in
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#eometric Isomerisms inCycloalkanes
9eometric isomers ha+e the same molecular
/ormula and the same order o/ attachment buta di//erent orientation in space that cannot beo+ercome b( rotation around a sbond.
+,-.Dimethlcclopentane0
H3C CH3
H3C CH3
H H
H3C H
H CH3
1,2-dimethylcyclopentane
cis-1,2-dimethylcyclopentane trans-1,2-dimethylcyclopentane
#eometric Isomerisms in
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#eometric Isomerisms inCycloalkanes
cis-1-tert-bt%l-4-meth%lc%clohe'ane
trans-1)2-!imeth%lc%clopropane
C
CCH
H3CH
CH3H
H
H3C
H H
C CH3
CH3H3C
H H
H H
H
H H
H
#eometric Isomerisms in
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#eometric Isomerisms inCycloalkanes
CH$
CH$
H
CH$
H
H$C
H
CH$
H$C
H
#eometric Isomerisms in
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#eometric Isomerisms inCycloalkanes
#eometric Isomerisms in
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#eometric Isomerisms inCycloalkanes
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