2. Dr. Damodar Koirala koirala2059@gmail.com
Content
• Organic compound definition
• Organic vs inorganic compound
• Classification of organic compound
• Formulas of organic compound
• Component of organic compounds (Alkyl and functional
group)
• Homologues series
• IUPAC nomenclature of organic compounds
2
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Introduction
• Organic chemistry is the branch of chemistry that deals with
the systematic study of organic compounds
• Historically, organic compounds were said to be obtained
from living sources only. eg: protein, fat, oil, sugar etc
• Currently, pure organic compounds are synthesized in
laboratory
3
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Introduction: Basic
• Carbon forms 4 bonds (Never more than 4 bonds)
• Nitrogen forms 3 bonds and have 1 lone pair electrons
• Oxygen forms 2 bonds and have 2 lone pair electrons
• Hydrogen forms 1 bond (Never more than 1 bond)
• Primarily, organic compounds contain covalent bond
4
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Origin of Organic compound
• Vital force theory
• Proposed by Berzelius in 1815
• “Organic compound can be formed only in presence of some
live force called vital force. This vital force is same force that is
keeping living being alive. It is impossible to synthesize
organic compounds in laboratory.”
5
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Failure of vital force theory
• Modern Definition: Organic compounds are hydrocarbons and
their derivatives
6
• In 1828, F. Wohler, a German scientist accidentally
synthesized urea in laboratory by heating mixture of
ammonium sulphate and potassium cyanate
(NH4)2SO4 + 2KCNO NH4CNO K2SO4
+
NH2CNH2
O
Urea
Rearrangement
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Organic vs inorganic compounds
7
S.No Organic Compound Inorganic Compound
1
Made up of few elements like C,
H, N, O, S, P etc
Made up of almost all known
elements
2 Contain covalent bond Covalent or ionic bond
3 Posses low mp and bp Posses high mp and bp
4 Isomerism is common Isomerism is less common
5 Reactions are slow Reactions are fast
6 About 50 lakh compounds known Only 1 lakh compounds are know
• These are also main reason for separate study of organic compound
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Isomerism
• Two or more compounds having same molecular formula but
different structures and physical properties are called isomers
• The phenomenon of forming isomers is called isomerism
8
CH3CHCH3
CH3
CH3CH2CH2CH3
( I ) ( II )
C4H10
2-methyl propane Butane
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Unique properties of carbon
• Tetravalency of carbon: The four valence electrons of carbon
atom prefer sharing with other four electrons of next element.
• Ionization energy and electronegativity: carbon has high
ionization energy (1085 KJ mol-1). Carbon is neutral with EN
2.5, which favors formation of covalent bond.
• Catenation: The process of forming covalent bond with atoms
of the same element.
• Multiple bond formation: Carbon atom can form double
bond or triple bond with other elements
10
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• Saturated: with no multiple bond
• Unsaturated: with at least one multiple bond
11
Classification of Organic compound
Ethane Propane
2-methyl propene propene Propyne
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• Straight chain: Carbon-carbon connection is one line only,
with no branches. No carbon is connected to more than 2
other carbons. It is like pole
• Branched chain: Carbon-carbon connection is in more
than one line, with branches. At least one carbon is connected
to more than 2 other carbons. It is like tree
12
Classification of Organic compound
Ethane Propane
3-methyl pentane
CH3-CH2-CH-CH2-CH3
CH3
CH3-CH-CH3
CH3
2-methyl propane
CH3-CH3 CH3-CH2-CH3
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Classification of Organic compound
• Acyclic or open-chain compounds: compounds with
open-chain structures
• Cyclic or closed-chain compounds: These compounds
have at least one ring (cyclic) system
•
13
propane
Cyclobutane
CH3-CH2-CH3
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Cyclic compound
• Homocyclic when the ring is formed by carbon atoms only.
• Heterocyclic contain one or more atom (usually O, N or S
atom) other than the carbon atoms.
14
Cyclopropane Cyclobutane Cyclopentane
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Cyclic compound
• Aromatic : with benzene like structure
• Alycylic: without benzene like structure
15
Benzene Pyridine
Cyclohexane Cyclopentane
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Formulas types
• Molecular formula: Actual composition of constituent
elements
• Empirical formula: Simplest whole number ration of
constituent elements
• Structural formula: All bonds are shown
• Contracted formula: Only major bonds are shown
• Electron dot formula: Bonds are represented by electron dot
• Bond line structural formula: Bond between carbon atoms
are shown as lines and the vertices and end of lines represent
carbon atoms
17
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Structural formula
• All the bonds are indicated among the concerned atoms
18
C
H
H
H C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
H
C
H
H
H C
H
Cl
H
C
H
H
H C
H
H
C
H
H
C
H
H
OH
C
H
H
H C
H
H
C
H
H
C
H
C
H
H
H
H
A B
C D
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Contracted formula
• Carbon-carbon bond and carbon-functional group bonds are
shown
19
C
H
H
H C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
H C
H
H
H C
H
H
C
H
H
C
H
H
OH
A B
CH3-CH2-CH2-CH2-CH2-CH3 CH3-CH2-CH2-CH2-OH
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Bond line formula
• Bond between carbon atoms are shown as lines and the
vertices and end of lines represent carbon atoms
20
C
H
H
H C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
H C
H
H
H C
H
H
C
H
H
C
H
H
OH
A B
CH3-CH2-CH2-CH2-CH2-CH3 CH3-CH2-CH2-CH2-OH
OH
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Organic compound
• Contains alkyl group and functional group
• Alkyl group is formed by removing one hydrogen from alkane
• Functional group is an atom or group of atoms linked with
carbon that determines characteristic properties of the
organic compound
21
Alkyl group Functional group
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Alkyl group
• Their general formula is CnH2n+1
• Alkane - ane + yl
22
S.No Formula Alkane Alkyl Formula
1 CH4 Methane Methyl- -CH3
2 C2H6 Ethane Ethyl- -C2H5
3 C3H8 Propane Propyl- -C3H7
4 C4H10 Butane Butyl- -C4H9
5 C5H12 Pentane Pentyl- -C5H11
6 C6H14 Hexane Hexyl- -C6H13
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Significance of Functional group
23
• All compounds with same functional group belongs to same
class
• The naming of organic compound is done on the basis of
function group
• The reactivity of organic compound is determined by its
functional group
• All compounds with same functional group have similar
chemical properties
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Functional group
24
Family Functional
group
Alkene C=C
Alkyne C≡C
Alcohol -O-H
Ether -O-
Halide -Cl, -Br, -F or -I
Aldehyde -CHO
Ketone -CO-
Amine -NH2
Ester -COO-
Carboxylic
acid
-COOH
Nitro -NO2
Cyanide -CN
Isocyanide -NC
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Homologues series
• A systematic order of structurally similar organic compounds,
containing the same functional group in which two adjacent
members differ in their molecular formula by a -CH2- unit.
• Each member of series is called homologue and the phenomenon is
called homology
25
Homologous series of alkane
Formula IUPAC Name
CH4
CH3-CH3 Ethane
CH3-CH2-CH3
CH3-CH2-CH2-CH2-CH3 Pentane
CH3-CH2-CH2-CH2-CH2-CH3
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Homologues series
26
Homologous series of alkene
Formula IUPAC Name
CH2=CH2
CH2=CH-CH3 Propene
CH2=CH-CH2-CH3
CH2=CH-CH2-CH2-CH3 Pent-1-ene
CH2=CH-CH2-CH2-CH2-CH3
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Homologues series
27
Homologous series of alcohol
Formula IUPAC Name
CH3OH Methanol
CH3-CH2-OH
CH3-CH2-CH2-OH
CH3-CH2-CH2-CH2-OH Butan-1-ol
CH3-CH2-CH2-CH2-CH2-OH
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Homologues series
28
Homologous series of haloalkane
Formula IUPAC Name
CH3Cl
CH3-CH2-Cl
CH3-CH2-CH2-Cl 1-chloropropane
CH3-CH2-CH2-CH2-Cl
CH3-CH2-CH2-CH2-CH2-Cl
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Homologues series
29
Homologous series of Ketone
Formula IUPAC Name
CH3-CO-CH3
CH3-CO-CH2-CH3
CH3-CO-CH2-CH2-CH3 Pentan-2-one
Homologous series of aldehyde
Formula IUPAC Name
HCHO
CH3-CHO
CH3-CH2-CHO Propanal
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Homologues series: Characteristics
• All member of homologous series have same functional group
• Homologues posses similar chemical properties but different
physical properties
• Homologues can represented by same general molecular
formula and have similar structure
• Two regular members of a homologous series differ by -CH2-
unit i.e 14 amu mass
• Homologues can be prepared by same general methods
30
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Nomenclature
• Common system: There was no systematic basis for
naming them and it was very difficult task to remember the
names of so many organic compounds. Even the same
compound was known by different names.
• IUPAC system: In order to bring uniformity and rationality
in naming the organic compounds throughout the world,
International Union of Chemistry (in 1958) came out with a
system of nomenclature later known as IUPAC (International
Union of Pure and Applied Chemistry) system.
31
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Nomenclature
32
C
H
H
H C
H
H
C
C
H
C
H
Br
C
H
H
C
H
H
H
H
H
H
Br
CH3-CH2-CH-CH-CH2-CH3
CH3
Longest chain =Parent chain
Alkyl =Branch
Not Alkyl =Functional Group
Longest chain =Parent chain
Alkyl =Branch
Not Alkyl =Functional Group
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IUPAC system
33
Root word Suffix
Prefix
Primary Secondary
Nature of
carbon chain
Function group
Longest
Carbon chain
Function group
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IUPAC system
• Tells exact structure of the molecule
• The organic molecules consist of following parts:
• Prefix(es) + word root + primary suffix + secondary
suffix
• Eg: Ethanol
34
Word root = Eh
Primary suffix = ane
Secondary suffix = ol
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IUPAC system
• Alkane with no branches i.e. straight chain
• Alkane with 1 branch
• Alkane with multiple branches
• Alkene and Alkyne
• Mono-functional group
• Poly-functional groups
• Naming cyclic hydrocarbon
35
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Straight chain alkane
• The name consist of two parts: word root + suffix
• Word root designates the number of carbon atoms in the
chain
36
No. Of C
atoms
Word root No. Of C-
atoms
Word root
1 meth- 6 hex-
2 eth- 7 hept-
3 prop- 8 oct-
4 but- 9 non-
5 Pent- 10 Dec-
• Suffix is -ane
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Nomenclature of alkane with 1 branch
For branched alkane, more than one chain is possible.
Rule 1: Longest chain rule: Identify the longest possible chain and
write word root.
38
CH3CHCH2CH2CH3
CH3CH2CHCH2CH3
CH3
CH3CHCH2CH2CH3
CH2CH3
CH3
Longest chain =
Word root =
Longest chain =
Word root =
Longest chain =
Word root =
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Nomenclature of alkane with 1 branch
Rule 2: Lowest number: The longest carbon chain is numbered
from one end to another. The numbering is done in such a way
that the substituted carbon atoms have the lowest possible
numbers.
39
CH3CH2CHCH2CH3
CH3
CH3CHCH2CH2CH3
CH2CH3
CH3CHCH2CH2CH3
CH3
Word root =
Primary suffix =
Position-substitution =
Word root =
Primary suffix =
Position-substitution =
Word root =
Primary suffix =
Position-substitution =
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Nomenclature of alkane with 1 branch
Rule 3: Name as follow
Position of substituent - Name of substituent Word root + Suffix
40
CH3CH2CHCH2CH3
CH3
CH3CHCH2CH2CH3
CH2CH3
CH3CHCH2CH2CH3
CH3 Word root =
Primary suffix =
Position-substitution =
Word root =
Primary suffix =
Position-substitution =
Word root =
Primary suffix =
Position-substitution =
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Nomenclature of alkane with >1 branches
Rule 1: Longest chain rule: Identify the longest possible chain
and write word root
41
CH3CHCHCH2CH3
CH2CH3
CH2CH3
CH3CHCH2CHCH3
CH3 CH3
CH3CHCHCH2CH3
CH3
CH3
Longest chain =
Word root =
Longest chain =
Word root =
Longest chain =
Word root =
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Rule 2: Lowest sum rule: The sum of numbers used to indicate
the positions of various alkyl groups must be the lowest
42
CH3CHCHCH2CH3
CH2CH3
CH2CH3
CH3CHCH2CHCH3
CH3 CH3
CH3CHCHCH2CH3
CH3
CH3
Nomenclature of alkane with >1 branches
Word root =
Primary suffix =
Position-substitution =
Word root =
Primary suffix =
Position-substitution =
Word root =
Primary suffix =
Position-substitution =
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Rule 4:Naming the same alkyl groups
- di (for two), tri (for three), the positions are separated by commas (,)
43
Nomenclature of alkane with >1 branches
CH3CHCH2CHCH3
CH3 CH3
CH3CHCHCH2CH3
CH3
CH3
Word root =
Primary suffix =
Position-substitution =
Word root =
Primary suffix =
Position-substitution =
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Rule 5: Naming different alkyl substituents, uses lowest sum rule
-names are written in the alphabetical order. However, the prefixes
di, tri, etc. are not considered in deciding the alphabetical order.
44
CH3CCHCH2CH3
CH2CH3
CH2CH3
Nomenclature of alkane with >1 branches
CH3CHCHCH2CH3
CH3
CH2CH3
Word root =
Primary suffix =
Position-substitution =
Word root =
Primary suffix =
Position-substitution =
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Rule 6: Naming different alkyl substituents
If two substituents are found in equivalent position, the lower
number is given to the one that comes first in alphabetical order
45
CH3CHCHCH2CH3
CH2CH3
CH2CH3
Nomenclature of alkane with >1 branches
Word root =
Primary suffix =
Position-substitution =
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Rule 7: If two longest chain is possible, then the one with more
number of substituents is preferred.
46
CH3CHCHCH2CH3
CH2CH3
CHCH3
CH3
Nomenclature of alkane with >1 branches
Word root =
Primary suffix =
Position-substitution =
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Nomenclature of Acyclic Hydrocarbons
47
Class of compound Suffix General name
Satutated -ane alkane
Double bond -ene alkene
Triple bond -yne Alkyne
Compound Word root Suffix Name
CH3-CH3 Eth- -ane Ethane
CH3-CH2-CH3 Prop- -ane Propane
CH3-CH=CH2 Prop- -ene Propene
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Naming Alkene/Alkyne
48
Nature of carbon chain Primary suffix General Name
Single bond ( C-C) -ane Alkane
Double bond ( C=C) -ene Alkene
Triple bond ( C≡C ) -yne Alkyne
Rule 1: Same as Alkane except the primary suffix is changed.
Rule 2: For branched compound, make sure multiple bond is
included in longest chain
Rule 3: For compound with longest chain more than 3 carbons,
indicate the starting position of multiple bond before the suffix
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Naming Functional group
51
Class Function Group Suffix/Prefix General name
Alcohol -OH -ol Alkanol
Aldehyde -CHO -al Alkanal
Ketone -CO- -one Alkylalkanone
Carboxylic acid -COOH -oic acid Alkanoic acid
Ester -COO- -oate Alkyl alkanoate
Cyano -CN -nitrile Alkanenitrile
Amino -NH2 -amine Alkanamine
Ether -O- Alkoxy- Alkoxyalkane
Halide -X halo- Haloalkane
Nitro -NO2 nitro- Nitroalkane
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Naming Functional Group
52
Rule 1: Same as Alkane except remember to add prefix or suffix
Rule 2: Make sure the functional group is included in longest
chain. If Carbon is part of functional group (like -CN, -CHO, -
COOH) then it must be part of parent chain.
Rule 3: Make sure to include position number if positional
isomer is possible for given compound. Position number always
goes in-front of functional group.
Overall Rule:The longest chain of carbon atoms containing the
functional group is numbered in such a way that the functional
group is attached at the carbon atom possessing lowest possible
number in the chain.
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Naming Alcohol
53
Functional
group
-OH
General
formula
CnH2n+1OH Representation R-OH
R is alkyl group and can not be hydrogen i.e n > 0
Naming Alkan - position - ol
*Include the position number only if longest chain contain more than 2 C
CH3-CH-CH2-CH2-CH3
OH
CH2-CH3
OH
CH3CH2CHCH2CH3
OH
CH3-CH2-CH2-OH
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Naming Haloalkane
54
Functional
group
-X
General
formula
CnH2n+1X Representation R-X
R is alkyl group and can not be hydrogen i.e n > 0
Naming Position-haloalkane (chloro, bromo, fluoro, iodo)
*Include the position number only if longest chain contain more than 2 C
CH3-CH2-CH2Br
Cl-CH2CH3
CH3-CH-CH3
F
CH3-CH-CH-CH3
I
CH3
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Naming Aldehyde
55
Functional
group
-CHO
General
formula
CnH2n+1CHO Representation RCHO
R is alkyl group and can be hydrogen i.e n = 0,1,2…
Naming Alkanal
*No need to include the position, it is always in position one
H-CHO
CH3-CH2-C-H
CH3-CH2-CH2-CHO
CH3CH2CHCH2CH3
CHO
O
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Naming Ketone
56
Functional
group
-CO
General
formula
CnH2n+2CO Representation RCOR’
R and R’ can not be hydrogen i.e n > 1 (if one of them is H it’s aldehyde)
Naming Alkan-position-one
*Include the position number only if longest chain contain more than 4 C
CH3CH2COCH3
CH3CH2COCH2CH3
CH3-C-CH3
O
CH3-CH2-CH2-C-CH3
O
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Aldehyde vs Ketone
57
Functional
group
General formula Representation
Aldehyde -CHO CnH2n+2CO RCHO
Ketone -CO- CnH2n+2CO RCOR’
In ketone both side to -CO- must be alkyl group, but in aldehyde one
side of -CO- must be hydrgoen
CH3-CHO
CH3-CO-CH3
CH3-CH2-C-CH3
O
H-C-H
O
CH3CH2CH2CCH2CH3
O
CH3CH2CH2CH2CH
O
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Naming Nitro compound
58
Functional
group
-NO2
General
formula
CnH2n+1NO2 Representation RNO2
R are alkyl group and can not be hydrogen i.e n > 0
Naming Position-nitroalkane
*Include the position number only if longest chain contain more than 2 C
CH3-CH2-NO2
CH3CH2CHCH2CH3
NO2
CH3CHCH3
NO2
CH3-CH2-CH2NO2
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Naming Ether
59
Functional
group
-O-
General
formula
CnH2n+2O Representation R-O-R’
R and R’are alkyl group and can not be hydrogen i.e n > 1
Naming Alkoxyalkane ( alkane for longest chain)
*Position is not required
CH3-O-CH3
CH3-CH2-O-CH2-CH2-CH3
CH3CH2OCH3
CH3CH2OCH2CH3
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Naming Ester
60
Functional
group
-COO-
General
formula
CnH2nO2 Representation R-COO-R’
R can be H but R’ can not be hydrogen ( R’ = H is acid)
Naming Alkyl alkanoate (alkanoate for R-COO and alkane for R’)
*Position is not required
CH3COOCH3 CH3-CH2-C-O-CH3
=
O
CH3COCH2CH3CH3
=
O
CH3-CH2-O-C-CH3
=
O
HCOOCH3
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Naming Carboxylic acid
61
Functional
group
-COOH
General
formula
CnH2nO2 Representation R-COOH
R can be H i.e n > 1
Naming Alkanoic acid
*Position is not required
CH3COOH CH3-CH2-C-OH
=
O
HOCCH2CH3CH3
=
O
CH3CH2CH2COOH
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Ester vs Carboxylic acid
62
Functional
group
General formula Representation
Acid -COOH CnH2n+2CO RCOOH
Ester -COO- CnH2n+2CO RCOOR’
In R’ in ester can not be “H”. Otherwise in both case R can be
hydrogen
CH3COOH
CH3COOCH3
CH3CH2COCH3
O
H-C-OH
O
CH3CH2CH2COCH2CH3
O
CH3CH2CH2CH2COH
O
H-C-O-CH3
O
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Naming Amine
63
Functional
group
-NH2
General
formula
CnH2n+1NH2 Representation R-NH2
R can not be H i.e n > 0
Naming Alakan-position-amine
*Include the position number only if longest chain contain more than 2 C
CH3CH2NH2
CH3CHCH3
NH2
H2NCH2CH2CH3
CH3CH2CHCH3
NH2
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Naming Cyano / Nitrile
64
Functional
group
-CN
General
formula
CnH2n+1CN Representation R-CN
R can not be H i.e n > 0
Naming Alakanenitrile (the carbon in nitrile is also used in alkane)
*Position is not required
CH3CN
CH3CH2
CN
NCCH2CH2CH3
CH3CH2CHCH3
CN
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Naming isocyanide
65
Functional
group
-NC
General
formula
CnH2n+1NC Representation R-NC
R can not be H i.e n > 0
Naming alkylisocyanide (carbon in -NC is not counted in alkyl)
*Position is not required
CH3NC
CH3CH2
NC
CH3CH2CH2NC
CH3CH2CHCH3
NC
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Secondary suffix: Functional group
66
• If the secondary suffix begins with a vowel, then the terminal
‘e’ of the primary suffix is removed before adding the
secondary suffix
Word root =
Primary suffix =
Secondary suffix =
CH3CH2CH2NH2
Word root =
Primary suffix =
Secondary suffix =
CH3CH2OH
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Secondary suffix: Functional group
• If the secondary suffix begins with a consonant, then the
terminal ‘e’ of the primary suffix is retained and secondary
suffix is added
Word root = Prop
Primary suffix = ane
Secondary suffix = nitrile
Prop + ane + nitrile= Propanenitrile
CH3CH2CN
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General formula
• Alkane : CnH2n+2
• Alkene / Cycloalkane: CnH2n
• Alkyne: CnH2n - 2
• Alcohol / Ether: Cn H2n+2 O
• Aldehyde / Ketone: Cn H2n O
• Carboxylic acid / Ester: Cn H2n O2
• Haloalkane : Cn H2n+1 X
• Amine: Cn H2n+1 NH2
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Determine organic compound
A B
C
D E F
G H I
CH3-CH2-COOH
CH3-CH2-Br
CH3-CH2-COO-CH3
CH3-CH2-O-CH3
CH2=CH2 CH3-CH2-CH3
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Name organic compound
A B
C
D E F
G H I
CH3-CH2-COOH
CH3-CH2-Br
CH3-CH2-COO-CH3
CH3-CH2-O-CH3
CH2=CH2 CH3-CH2-CH3
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Nomenclature of poly-functional organic
compounds
• In case of polyfunctional compounds, one of the functional groups
is chosen as the principle functional group
• The compound is named on the basis of principle functional group
• The remaining functional groups are named as substituents using
appropriate prefix
• If more than on functional group of the same type are present,
their number is indicated by addition di, tri etc before the class
suffix.
• The preference of principal functional group on decreasing priority
is
• -COOH, -COOR, -CN, -CHO, -CO-, -OH, -NH2, C=C…
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Priority of functional group
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Class Function group Prefix
Carboxylic acid -COOH carboxyl
Ester -COO- carbalkoxy
Acid Chloride -COCl haloakanoyl
Acid amides -CONH2 carboxamido
Nitrile -CN cyano
Aldehyde -CHO Formyl
Ketone -CO- Oxo
Alcohol -OH hydroxyl
Amines -NH2 amino
Alkene C=C -
Alkyne C≡C -
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Nomenclature of poly-functional organic
compounds
CH3CHCH2CH2COH
O
OH
CH3CHCH2CH2CH2Cl
OH
CH3-CH-CH2-CH2-CH2-Cl
Cl
CH3CHCH=CHCH3
Br
CH2=CHCH=CHCH3 CH3-CH(Br)-CH(NH2)-COOH
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Primary Prefix: cyclo for cyclic
CH2
H2C CH2
CH2
H2C CH2
H2C
CH2
H2C CH2
H2C
CH2
Primary prefix
Word root
Primary suffix
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Name to structure
1. Identify parent chain (longest chain)
2. Identify if any branches are present
3. Identify if functional groups are present
4. Identify the position of branch/functional group
5. Draw longest chain, number one end to another, but
branch/functional group in appropriate carbon, add
hydrogen to make 4 bonds to carbon, finally double check
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Name to structure
1. 2,3-dimethylbutane
2. 3-hydroxypentanal
3. Butan-2-one
4. Hexanal
5. Propanoic acid
6. Methoxyethane
7. Butan-1,3-diol
8. 3-ethyl-2-methylhexane
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Nomenclature of Benzene derivatives
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For many of the derivatives, simply prefix the name of the
substituent group:
Chlorobenzene Nitrobenzene
Bromobenzene Iodobenze
Phenol Benzoic acid
Toluene
Aniline Benzenesulfonic
acid
Derivatives with special name:
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o-chloronitrobenzene m-chlorobenzenesulfonic acid
Nomenclature of Benzene derivatives
79
If two groups are attached to benzene ring, indicate their relative positions by using
ortho, meta, and para.
o-Dichlorobenzene m-Dichlorobenzene p-Dichlorobenzene
Two different groups with no special group: the two groups are successively named
and end the word with -benzene.
Two different groups with a special group: the compound is name as a derivative of
that special compound.
m-bromochlorobenzene p-chlorophenol
ortho meta
para
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Nomenclature of Benzene derivatives
80
If more than two groups are attached to benzene ring, numbers are used to indicate their
relative positions.
1. If all groups are the same, each is given a number, the sequence being the one that
gives the lowest combination of number.
1,2,4-trichlorobenzene 3,5-dichloronitrobenzene
2. If the groups are different, then the last-named group is understood to be in position 1
and the other numbers conform to that.
3-bromo-4-chlorophenol
3. If one of groups that gives a special name is present, then the compound is named as
having the special group in position 1.