8/2/2019 Fundamentals of Organic Chemistry 2
1/37
Fundamental of Organic Chemistry
-Functional group and homologous series
-Isomerism-Structure and shape of organic
compounds
-Nomenclature
-Structure determination
-Stereoisomerism
8/2/2019 Fundamentals of Organic Chemistry 2
2/37
Functional groups
Functional group is an atom or a group of atoms
which determine the properties of a
homologous series.Examples : alkanoic acid / carboxylic acid
C O H
O
8/2/2019 Fundamentals of Organic Chemistry 2
3/37
Homologous seriesHomologous series is a series of compound in whicheach member differs from the next by a
CH2 group
All members:
Can be prepared by similar methods
e.g. preparation of ethanoic acid
Have similar chemical properties and graded
physical properties.e.g. Both ethene and propene decolourize Br2 quickly.
Boiling point of methane and ethane are gradually
increased.
8/2/2019 Fundamentals of Organic Chemistry 2
4/37
Homologous series
All members
Can be represent by a
General formula (which also shows the
functional groups the members bear)
Examples : (in handouts)
8/2/2019 Fundamentals of Organic Chemistry 2
5/37
Homologous series
FunctionalGroup
GeneralFormulae
Name Examples
Saturatedhydrocarbon
CnH2n+2 alkane CH4methane
CnH2n alkene ethene
-CC- Cn
H2n-2
alkyne ethyne
8/2/2019 Fundamentals of Organic Chemistry 2
6/37
Homologous series
arene benzene
saturatedring
CnH2n cycloalkane cyclohexane
-X RXCnH2n+1X
haloalkane chloroethane
8/2/2019 Fundamentals of Organic Chemistry 2
7/37
R : Alkyl group
CnH2n+2 Alkane CnH2n+1 Alkyl group
CH4 methane CH3 Methyl
C2H6 ethane C2H5 ethyl
C3H8 propane C3H7 propyl
CH3CHCH3 methylethyl
8/2/2019 Fundamentals of Organic Chemistry 2
8/37
Homologous series
-OH ROHCnH2n+1OH
alkanol ethanol
-O- R-O-R
CnH2n+1OCmH2m+1
ether ethoxyethane
(-CHO) RCHO alkanal ethanal
C H
O
CnH2n+2O
Cn+mH2(n+m)+2O
CnH2n+2O
CnH2n+1CHO
CnH2nO
8/2/2019 Fundamentals of Organic Chemistry 2
9/37
Homologous series
alkanone
butan-2-one
-COOH RCOOH alkanoic
acidethanoic
acid
-COOR RCOOR ester methylethanoate
C
O
C R'R
O
8/2/2019 Fundamentals of Organic Chemistry 2
10/37
-COX RCOX alkanoyl
halide
ethanoyl
chloride
acidanhydride
ethanoic
propanoicanhydride
-NH2 RNH2CnH2n+1NH2CnH2n+3N
amine methanamine
C
O
ClCH3
CO
O
C
O
CO
O
C
O
R R'
CO
O
C
O
CH3 CH2CH3
NH2C
H
H
H
8/2/2019 Fundamentals of Organic Chemistry 2
11/37
-NO2 RNO2 nitro-compounds
CH3CH2NO2nitroethane
-CN R-CN cyano-compound
(carbonitriles)
ethanenitrile
-CONH2 Acid amide CH3CONH2
ethanamide
8/2/2019 Fundamentals of Organic Chemistry 2
12/37
Isomerism
Isomerism
Isomer - same molecular formula but
not identical.
Isomerism
Structural Isomerism Stereoisomerism
8/2/2019 Fundamentals of Organic Chemistry 2
13/37
Structural isomerism
Structural isomers having same
molecular formula but differ in the
sequence in which their atoms are linkedtogether, i.e. different structural
formula :
8/2/2019 Fundamentals of Organic Chemistry 2
14/37
Unsaturation index
Unsaturation index = No. ofcarbonatoms No. ofhydrogen atoms / 2
No. ofhalogen atoms / 2 + No. ofnitrogen atoms / 2 +1
Unsaturation index = (C) - (H)/2 - (X)/2 +(N)/2 +1
If unsaturation index = 1 : a double bond / ringIf unsaturation index = 2 : two double bonds /rings OR one triple bond OR one d.b. + one ring
8/2/2019 Fundamentals of Organic Chemistry 2
15/37
Examples
C6H6 : 6 6/2 + 1 = 4
3 d.b. + 1 ring
C6H12O : 6 12/2 + 1 = 1
1 d.b.
C3H5N : 3
5/2 + 1/2 + 1 = 21 t.p.
8/2/2019 Fundamentals of Organic Chemistry 2
16/37
C6H12O
Unsaturation index = 1
Identify possible functional groups :
OH,
O ,
CHO,CO , etc
Try aldehyde CHO
8/2/2019 Fundamentals of Organic Chemistry 2
17/37
C6H12O the aldehydes
Start with longest continuous carbon chain :
H
O
H
O
Shorten the longest continuous carbon chain,
and consider the removed CH3 group :
H
O
H
O
H
O
8/2/2019 Fundamentals of Organic Chemistry 2
18/37
Continue to shorten the longest continuous carbon chain :
H
O
Put back the two carbon either two methyl groups or,
One ethyl group
H
O
H
O
H
O
H
O
H
O The left one is repeated as
the longest carbon chain
also consists of 5 carbon
C6H12O the aldehydes
8/2/2019 Fundamentals of Organic Chemistry 2
19/37
Can we continue to shorten the longestcontinuous carbon chain ?
C6H12O the aldehydes
H
O
No, because this would increase the no. ofcarbon in the longest continuous carbon chainand this would give a structure we have drawnbefore.
8/2/2019 Fundamentals of Organic Chemistry 2
20/37
C6H12O the aldehydes
In the above example, we havent consider the positionof functional group because the aldehyde functionalgroup must be in the terminal end of a chain.
If it is ketone, the functional group a C = O would beat the middle of the chain :
O
O
O=
8/2/2019 Fundamentals of Organic Chemistry 2
21/37
C5H10
Unsaturation index = 5 10/2 + 1 = 1
It can bear a double bond or a ring.
C C C CC
H
H
HH
H
H
H
H
H
H =
=
8/2/2019 Fundamentals of Organic Chemistry 2
22/37
C4H7Cl
Unsaturation index = 4 7/2 + 1 1/2 = 1
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
8/2/2019 Fundamentals of Organic Chemistry 2
23/37
Functional group isomers
Isomerism occurs between members of two
different homologous series (which have same
general formula).Examples : Ketone and Aldehyde CnH2nO
C3H6O
O
H
HH
HH
H H
HH
H
O
HH
8/2/2019 Fundamentals of Organic Chemistry 2
24/37
Alcohol and ether CnH2n+2O
Examples : C3H8O
Functional group isomers
OH
O
8/2/2019 Fundamentals of Organic Chemistry 2
25/37
Carboxylic acid and ester CnH2nO2
Example : C3H6O2
Functional group isomers
O
O
OH
O
H O
O
8/2/2019 Fundamentals of Organic Chemistry 2
26/37
Effect of relative sizes of alkyl group
and functional group on physical
properties of compounds
Boiling point Boiling point depends on intermolecular force.
Stronger intermolecular forces
higherb.p.
Intermolecular force : Van der Waals force
and H bond
Compounds which can form H
bondwould have higher boiling point :
8/2/2019 Fundamentals of Organic Chemistry 2
27/37
Boiling point of a homologous series
Within the same homologous series, b.p. increased
gradually with the carbon atoms increased.
But the difference in b.p. between consecutive
members of the homologous series become smaller.
B.p.
No. of carbon atoms
8/2/2019 Fundamentals of Organic Chemistry 2
28/37
In alkanol In amine
Most of them are liquids in room temperature and pressure.
H bond formation in Organic compounds
O H OH
N H
H
NH
H
8/2/2019 Fundamentals of Organic Chemistry 2
29/37
H bond formation in Organic
compounds
In carboxylic acid In acid amide Liquids and solids
Benzenecarboxylic acid is a white crystalline solid.
O
O H
O
O
H
O
O
H
O
N H
H
O
N
H
H
O
N
H
H
8/2/2019 Fundamentals of Organic Chemistry 2
30/37
Melting point
It has a similar trend in b.p.
But in case of alkanes and carboxylic acids, an
even member of the series has a higher m.p.
than the odd member immediately below (or
even above) it.
Melting
point
No. of carbon atoms
8/2/2019 Fundamentals of Organic Chemistry 2
31/37
Melting point
This is because in even member, different
chains packed closer together than for the
odd member, thus larger theattractive force.
8/2/2019 Fundamentals of Organic Chemistry 2
32/37
Solubility in water
It involves two kinds of energy when a substance
dissolves in water :
Energy required to break the bond /overcome the force of attraction
between solute particles
(intermolecular force).
Energy released when the attractiveforcesformed by the water molecule and the
solute particles.
8/2/2019 Fundamentals of Organic Chemistry 2
33/37
Solubility in water
Size of molecule
Solubility decreases with increasing
chain length as the intermolecular force becomestronger more energy required tobreak the bond.
Example : Ethanol is soluble in water in allproportion while hexan-1-ol is only slightlysoluble.
8/2/2019 Fundamentals of Organic Chemistry 2
34/37
Formation of H bond
Those compounds which can form extensive H
bond with water has higher solubility in water :
Solubility in water
O
N H
H
O
H
H
O
HH
O
HH
O
H
H
O
H
HOther homologous
series includescarboxylic acid,
alkanol and amine.
8/2/2019 Fundamentals of Organic Chemistry 2
35/37
For alkanals, ketones, etc. they are only slightly
soluble in water unless the molecular size is
small :
Solubility in water
H H
O
O
H
H
O
H
H
CH3
CH3
O
O
H
H
O
H
H
8/2/2019 Fundamentals of Organic Chemistry 2
36/37
Physical properties of structural isomers
Butyl alcohols :
Density B.P. /o
CCH3CH2CH2CH2OH 0.810 118
(CH3)2CHCH2OH 0.802 108
CH3CH2CH(CH3)OH 0.806 100
(CH3)3COH 0.789 83
8/2/2019 Fundamentals of Organic Chemistry 2
37/37
Boiling points decrease as branching increases
Branching of carbon chain gives a more sphericalshape to the molecules and reduces the extent ofcontact between molecules
Weaker intermolecular force
No regularity in the change in m.p. as the packing in
solid state may varyDensity of branching alcohol is also lower than itsstraight chain isomers.
Physical properties of structural isomers
Top Related