1
Nomenclature
of Organic
Compounds
The purpose of the IUPAC system of nomenclature
is to establish an international standard of naming
compounds to facilitate communication. The goal
of the system is to give each structure a unique
and unambiguous name, and to correlate each
name with a unique and unambiguous structure.
In this Chapter, we will develop the knowledge of
using IUPAC conventions for naming an organic
compound and to write the appropriate structure of
a compound from its given IUPAC name.
Learning Framework
of the Chapter . . .
1-1 Introduction
Because of infinitely large number of organic compounds
existing already and several new compounds being either
synthesized or discovered everyday, each specific compound
requires a unique name so that it can be recognized all over the
world by that name. Just as each distinct compound has a unique
molecular structure which can be designated by a structural
formula, so each compound must be given a characteristic and
unique name.
1-1 Introduction
1-2 Naming Hydrocarbons According to IUPAC
Conventions
1-3 Naming Compounds Containing One or More
Similar Type of Principal Functional Groups
1-4 Naming Compounds Containing More Than
One Type of Principal Functional Groups
1-5 Nomenclature of Bicyclic Compounds
1-6 Nomenclature of Spiro Compounds
2 Essential Organic Chemistry
As organic chemistry grew and developed, many compounds were given trivial names, which are now commonly used
and recognized. Some examples are
Name Methane
Butane Acetone Toluene Acetylene
Ethyl alcohol
C4H10
CH3COCH3 CH3C6H5 C2H2
C2H5OH
Formula CH4 Such common names often have their origin in the history of the science and the natural sources of specific compounds, but
the relationship of these names to each other is arbitrary, and no rational or systematic principles underly their assignments.
Earlier, organic compounds were named on the basis of their source or after the name of discoverer. Due to their large
number, it has becoming difficult for the scientific world to keep record of all organic compounds having typical names
originating from source, discoverer or place of discovery etc.
In order to keep track of such a large number of organic compounds with a wide range in complexity of their skeleton,
the “International Union of Pure and Applied Chemistry” (IUPAC) has set-up some standard conventions for systematic
naming of organic compounds so that they can be easily recognized from their names and their structure can be drawn using
IUPAC conventions.
1-1A The IUPAC Systematic Approach to Nomenclature
A rational nomenclature system should do at least two things. First, it should indicate how the carbon atoms of a given
compound are bonded together in a characteristic lattice of chains and rings. Second, it should identify and locate any
functional groups present in the compound. Since, hydrogen is such a common component of organic compounds, its
amount and locations can be assumed from the tetravalency of carbon, and need not be specified in most cases. The IUPAC
nomenclature system is a set of logical rules devised and used by organic chemists to circumvent problems caused by arbitrary
nomenclature. Knowing these rules and given a structural formula, one should be able to write a unique name for every
distinct compound. Likewise, given a IUPAC name, one should be able to write a structural formula. In general, an IUPAC
name will have three essential features
•• A root or base indicating a major chain or ring of carbon atoms found in the molecular structure.
•• A suffix or other element(s) designating functional groups that may be present in the compound.
•• Names of substituent groups, other than hydrogen, that complete the molecular structure.
As an introduction to the IUPAC nomenclature system, we shall first consider compounds that have no specific functional
groups. Such compounds are composed only of carbon and hydrogen atoms bonded together by sigma bonds (all carbons are
sp3 hybridized).
According to IUPAC conventions, organic compounds are classified into two broad categories for the purpose of namingOne being “hydrocarbons” – which contain only carbon and hydrogen and other being “derivatives of hydrocarbon” which,
besides containing carbon and hydrogen, also contain some other atoms viz. oxygen, nitrogen, halogen, sulphur etc.
1-2 Naming Hydrocarbons According to IUPAC Conventions
1-2A Saturated Unbranched-Chain Hydrocarbons
The first four saturated unbranched acyclic (non-cyclic) hydrocarbons are called methane, ethane, propane and butane.
Names of higher members of this series consist of a numerical term followed by “ane”. Examples of few unbranched,
saturated, acyclic hydrocarbons are shown in the Table 1.1.
Table 1.1 (n = Total number of carbon atoms)
n
Name
n
Name
n
Name
5
6
7
8
9
10
11
12
13
Pentane
Hexane
Heptane
Octane
Nonane
Decane
Undecane
Dodecane
Tridecane
14
15
16
17
18
19
20
21
22
Tetradecane
Pentadecane
Hexadecane
Heptadecane
Octadecane
Nonadecane
Icosane
Henicosane
Docosane
23
24
25
26
27
28
29
30
40
Tricosane
Tetracosane
Pentacosane
Hexacosane
Heptacosane
Octacosane
Nonacosane
Triacontane
Tetracontane
n
50
60
70
80
90
100
Name
Pentacontane
Hexacontane
Heptacontane
Octacontane
Nonacontane
Hectane
Nomenclature of Organic Compounds Chapter 1 3
1-2B Structural Formula and Bond-Line Structure
Structural formula of a compound demonstrate the connectivity of atoms in the molecule ie, it represents a specific
bonding pattern, a characteristic of the given molecule. Some of the structural formula and its descriptions are mentioned
below :
CH3CH2CH2CH2CH2CH3
n-hexane
H H H H H H
H HH
H
H—C—C—C—C—C—C—C—H
H3C—CH—CH2CH2—C—CH2CH3
H C H H C H H
CH3
2, 5, 5-trimethyl heptane
H
HH
H
HH
H
C
H
C
C
H
H
C
H
C
C
H
H
H
H
C
C
H
H
H
H
C
C
H
H
H
H H H H C H H
CH3
CH3
H
H—C—C—C—C—C—C—H
H
H
H H H H H H
H
HH
C
H
H
H
HH
C
C
H
C
C
H
H
C
H
H
H HH
As shown in the above structures, carbon is tetravalent and associated with four covalent bonds (C—H or C—C bonds).
1-2Aa Bond-Line Structures (Topological Structures)
In frequent writing, organic molecules are usually represented by a line structure in which letters ‘C’ for carbon and ‘H’
for hydrogen are not shown. In topological structure, each point of inflexion and the terminal points represent carbon atoms
and the visible line between two points represents carbon-carbon bonds. At each carbon, the number of hydrogen equals to
(4–the no. of visible bonds at that carbon) eg,
H H H H H H
H—C—C—C—C—C—C—H =
H H H H H H
n-hexane
H
H
H
H H H H C H H
H—C—C—C—C—C—C—C—H=
H C H H C H H
H
HH
H
3C—C bonds
ie, one H
4C—C bonds
ie, no H
HH
2, 5, 5-trimethyl heptane
H
H
H
H
H
C
C
H
H
C
C
C
C
H
Cyclohexane
H
H H H
H =
H
H—C—C—C == C—H=
H C
H
H
HH
H
3-methyl-1-butene
4 Essential Organic Chemistry
1-2Ab Univalent Radicals
Univalent radicals derived from saturated unbranched hydrocarbons by removal of one hydrogen atom from a terminal carbon
atom are named by replacing –“ane” of the parent name by “yl”. The carbon atom with the free valence is numbered as 1.
4
3
2
1
CH3CH2CH2CH2—Butyl
10
1
H3C—(CH2)8—CH2—Decyl etc.
1-2C Saturated Branched-Chain Acyclic Hydrocarbon
In case of a saturated, branched chain hydrocarbon, following rules are applicable in the same sequence
Rule 1 Selection of the longest carbon chain : The longest carbon chain gives parent name to the compound.
Rule 2 Numbering the longest chain : Longest chain is numbered starting from a terminal carbon. Numbering is done
in such a way that lowest possible number is given to the side chain as
H 3C
(1)
CH3
CH3
Longest chain has seven carbon atoms. If we start numbering from the left terminal, side chain methyl group comes at 5th
carbon while if numbering starts from right terminal, side chain methyl group comes at 3rd carbon which is a lower number.
Hence, the correct way of numbering will be to start from the right terminal.
When more than one locants (side groups) are present, than that number series is “Correct” which contain the lowest
number on the occasion of first difference as
CH3
H 3C
CH3
CH
CH3
3
(2)
The two number series existing in compound (2) are 2,3,5 and 2,4,5. The first one is correct and second is incorrect.
Rule 3 When writing names of branched, saturated hydrocarbon, locants are written first in alphabetical order (irrespective of their numbers) followed by name of parent chain. Locants in the name must be followed by its number separated by
hyphen (-). If more than one locants of similar types are present at the same or different positions, di, tri etc. are prefixed
before the locants. Adjacent numbers must be separated by comma (,).
Applying the above mentioned rules, compounds (1) and (2) described just before can be named as
6
7
H 3C
5
4
3
2
H 3C
CH3
CH3
3-methylheptane
6
1
9
H3C
8
7
CH3
6
5
4
3
3
2
CH3 CH3
9
CH3
2
CH3
1
CH3
6-ethyl-2, 4-dimethyl nonane
(not 2,4-dimethyl-6-ethylnonane)
(In alphabetical order, initials of original
name of the locant is considered ie, ‘m’
of methyl is considered here not ‘d’ of di)
1
CH3
2, 3, 5-trimethyl hexane
(not 2, 4, 5-trimethyl hexane)
Some other examples applying the above rules are
H3C
5
4
H3C
8
CH3
7
H 3C
H3C
CH3
CH3
6
5
4
3
CH3
2
CH3
1
CH3
4-ethyl-2, 3, 6, 6, 8-pentamethyl-5-propylnonane
(not 6-ethyl-2, 4, 4, 7, 8-pentamethyl-5-propylnonane)
Nomenclature of Organic Compounds Chapter 1 5
Rule 4 When two different alkyl locants are equidistant from the two ends of main chain, they are numbered in
alphabetical order as
CH3
CH3
CH3
1
9
10
8
5
CH3
H3C
H3C
1
7 6 5 4 3 2
7
3
CH
8
6
4
3
9
2
CH3
4-ethyl-7-propyldecane
(not 7-ethyl-4-propyldecane)
3-ethyl-7-methylnonane
(not 3-methyl-7-ethylnonane)
Rule 5 Following common names are retained in IUPAC system for unsubstituted hydrocarbons only
CH3
CH3
H3C
CH3
CH3 H3C
H3C
Isobutane
CH3
CH3
CH3
H3C
CH3
Isopentane
CH3
Neopentane
Isohexane
Rule 6 Branching in the branch: If there is a complex branch which is branched further, branch is numbered separately
starting from the carbon directly bonded to parent chain and name of branch is written in small parenthesis ( ) before the name
of parent hydrocarbon as
13
12
10
11
H3C
8
7
9
5
H3C
3
4
2
6
1
5
4
2
1
CH3
3
Here the branch is dimethylpentyl as
complete single substituent
CH3 CH3
CH3
7-(1, 2-dimethylpentyl)-5-ethyltridecane [not 5-ethyl-7-(1,2-dimethylpentyl) tridecane]
In case where name of complex branch are composed of identical words, priority is given to that branch which has locants
at the lowest number as
4
H3C
3
2
H3C
12
13
H3C
H3C
1
10
11
9
8
2
1
4
3
CH3
8
6
7
4
5
H3C
2
3
CH3
7
5
6
CH3
4
2
H3 C
6-(1-methylbutyl)-8-(2-methylbutyl) tridecane
Both branch have the common word ‘‘butyl’’ therefore, branch at position 6
will have priority since, it has locant at C-1 while other has locant at C-2
3
1
CH3
CH3
4-isopropyl-5-propyloctane
Rule 7 The presence of identical complex branch, each substituted in the same way, may be indicated by the appropriate
multiplying prefix bis, tris, tetrakis, pentakis etc. The complete expression denoting such side chain may be enclosed in
parenthesis as
3
4
CH3
2
H3C
1
H3 C
10
H3C
8
7
9
6 54
1
H3 C
H3C
3
2
CH3
3
2
CH3
CH3
CH3 1
5,5-bis(1, 1-dimethylpropyl)-2-methyldecane
13
H3C
10
12
11
9
1
H3C
1
CH3
6
8
CH3
7
H3 C
2
CH3
2
3
3
4 5
CH3
5,5-dimethyl-6-(1,1-dimethylbutyl)-6-pentyltridecane
6 Essential Organic Chemistry
Rule 8 If chains of equal length are competing for selection as main chain in a saturated, branched acyclic hydrocarbons,
the choice goes in series to
(a) The chain, which has the greatest number of side chains
7
H3C
CH3
6
7
H3C
H3C
5
3
4
CH3
2
H3 C
CH3
1
CH3
7
5
CH3
3
4
CH3
2
1
1
3
5
CH3
4
CH3
CH3
CH3
(Two locants)
(Wrongly numbered)
(b) The chain whose side chain has lowest numbered locants
CH3
6
7
H3C
4
3
2
5
CH3
3
4
H3C
CH3
1
CH3
6
H3C
CH3
5
CH3
7
H3C
2
CH3
1
CH3
Wrongly numbered : locants
are at 2,4,6 positions
Correctly numbered (locants are at
2,4,5 positions) 4-isopropyl-2,5dimethylheptane
2
H3 C
CH3
CH3
6
H3C
(Three locants)
Correctly numbered (four locants)
2, 3, 5-trimethyl-4 propylheptane
6
(c) The chain having the greatest number of carbon atoms in the smaller side chain
H3C
H3C
H3C
13
H3 C
12
11
10
9
8 7
CH3 CH3
6
5
4
3
CH3
1
CH3
CH3
H3C
CH3
2
CH3
7,7-Bis(2,4-dimethylhexyl)-3-ethyl-5,9,11-trimethyltridecane
(d) The chain having the least branched side chain
CH3
12
H3C
H3C
10
11
CH3
9
8
7
6
5
4
3
1
2
CH3
6-(1-isopropylpentyl)-5-propyldodecane
1
CH3
12
H3 C
2
H3C
11
10
9
3
8
4
7
CH3
5
CH3
6
CH3
Wrongly numbered
CH3
Nomenclature of Organic Compounds Chapter 1 7
Problem 1-1 Write IUPAC names of the following hydrocarbons
I
II
III
IV
6
7
4
5
V
2
3
1
1
2
4
3
6
5
7
II
I
5-ethyl-3,3-dimethyl heptane
3-ethyl-5-methylheptane
When same number series (here 3,5) are Lower number coming at first occasion of
obtained from both terminals, preference difference determine the numbering
goes to alphabetical order.
pattern-here 3,3,5 not 3,5,5.
4
2
1
3
4
6
5
8
9
7
10
8
5
6-ethyl-3,4-dimethyl octane 6
Longest chain with maximum number of locants
becomes the parent chain.
4
3
1
2
5
6
7
V
3,5-diethyl-2,3,5,6-tetramethyl heptane
Longest chain with maximum number of locants becomes the parent chain.
Problem 1-2 Write. structural formula of the following hydrocarbons
(I )
(II )
(III )
(IV )
(V )
4-ethyl-2,2,6,6-tetramethyl heptane.
4-ethyl-2,3-dimethyl hexane.
6-ethyl-3-methyl-5-propyl nonane.
5-(1,2-dimethylpropyl )-5-(2,2-dimethylpropyl ) nonane.
5-(1,2-dimethylpropyl )-6-(1-ethylpropyl ) decane.
I
II
IV
1
2
IV
5-butyl-5-methyl-4-propyl decane
III
7
3
III
V
8 Essential Organic Chemistry
Problem 1-3 Write IUPAC names of the following hydrocarbons
I
II
III
IV
3
2
9
1
8
6
7
4
5
1
3
2
1
4
2
3
2
1
I
5-(1-ethyl-2, 2-dimethylpropyl)-5
-(1, 2, 2-trimethylpropyl) nonane
3
5
4
10
1
6
8
8-ethyl-2, 3, 8-trimethyl-4, 7-dipropyl decane
6
5
2
1
7
8
4
3
10
9
III
9
11
7
5
10
9
II
5-(1, 1-dimethylpropyl)-6(2, 2-dimethylpropyl) decane
2
3
8
7
6
IV
6, 7, 8-triethyl-3-methyl undecane
Problem 1-4 Draw structures of all alkanes and write their IUPAC name having molecular formula C7H16.
Heptane
2-methylhexane
2,4- dimethylpentane
2,3-dimethylpentane
3-methylhexane
3-ethylpentane
2,2-dimethylpentane
2,2,3,-trimethyl butane
1-2D Unsaturated Hydrocarbons
Rule 1 Unsaturated, unbranched acyclic hydrocarbons having one double bond are named by replacing “–ane” of the
name of corresponding saturated hydrocarbon with the ending “-ene”. If there are two or more double bonds, the ending will
be “-adiene”, “-atrine” etc. The chain is so numbered as to give lowest possible number to the double bond.
H3 C
1
2
4
3
3-heptene
6
5
CH3 H3C
7
1
2
4
3
6
5
2,4-heptadiene
8
CH3 H3C
7
5
7
6
1
3
4
1,3,5-octatriene
2
CH2
Nomenclature of Organic Compounds Chapter 1 9
Following unsystematic names are retained in IUPAC
CH2==CH2 (Ethene)
CH2==C==CH2 (Allene)
Rule 2 Unsaturated, unbranched, acyclic hydrocarbons having one triple bond are named by replacing the ending “-ane”
of corresponding saturated hydrocarbon with the ending “-yne”. If there are two or more triple bonds, the ending will be
“-adiyne”, “-atriyne” etc. The chain is so numbered as to give lowest possible number to the triple bond.
2
HC
2
4
H3C
CH3
3
1
CH3
3
1
5
6
4
Pentyne
(Its triple bond is at terminal positions,
therefore, it need not numbered)
7
8
5
H3C
5
6
2-hexyne
1
3
CH3
2
4
2,4,6-octatriyne
Rule 3 Unsaturated unbranched acyclic hydrocarbons, having both double and triple bonds are named by replacing
ending “-ane” from the name of the corresponding saturated hydrocarbons by “-enyne”, “-adienyne”, “-atrienyne” “-enediyne”
etc. Numbers as low as possible are given to double and triple bonds even though this at times gives “-yne” a lower number
than “-ene”.
6
4
2
H2C
3
1
2
CH
4
HC
5
CH3
3
1
3-penten -1-yne
1,3-hexadien-5-yne
5
Preference has been given to numbering 1,3 rather than to 2,4 and not to triple bond over double bond.
Rule 4 When there is a choice in numbering between double and triple bond (this occur when double and triple bonds
are equidistant from the two terminal), the double bonds are given lowest numbers(ene comes before yne in alphabetical
order).
4
5
HC
2
1
8
CH2
3
H3 C
7
5
6
1
CH3
3
4
2
CH3
1-penten-4-yne
Here both double bond and triple bonds are
equidistant from terminals hence, numbering is
done in alphabetical order.
4-methyl-6-octen-2-yne
Here both double bond and triple bonds are
equidistant from terminals hence, preference
goes to lower number to other locant.
Rule 5 Unsaturated branched acyclic hydrocarbons are named as derivatives of unbranched hydrocarbons which contain
maximum number of double and triple bonds.
2
6
HC
5
3
4
2
CH3
CH2
1
CH3
4
not HC
5
8
CH3
6
2
1
CH3
CH2
3
or HC7
6
4
5
1
CH3
CH2
3
8
CH3
7
3,4-dipropyl-1,3-hexadien-5-yne
Carbon chain with maximum number of double/triple bonds is
selected as parent chain though it contains less no. of
carbon than other longer chain but with lower no. of
double/triple bonds, existing in the molecule.
Rule 6 If there are two or more chain competing for selection as the chain with maximum number of unsaturated bonds,
then the choice goes to
10 Essential Organic Chemistry
(i) That one with greatest number of carbon atoms
1
CH2
8
7
H3C
5
6
2
1
3
4
CH2
2
7
5
3
H3C
5-vinyl-1,3,5-octatriene
CH2
4
CH2
6
The above numbering system also has
a main chain with three double bonds but one
carbon less than other chain (mentioned
on left)
(ii) If the number of carbon atoms being equal, the one containing maximum number of double bonds is selected as the
parent chain.
7
CH
7
H2C
5
6
6
1
3
4
CH2
2
CH
H2C
not
1
3
5
4
CH2
2
5-ethynyl-1,3,6-heptatriene
1
3
4
5
CH2
5
not
2
6
6 CH2
1
3
CH2
4
2
CH2
4-ethynyl-1,5-hexadiene
4-vinyl-1-hexen-5-yne
Following name is retained for unsubstituted compound only
CH3
CH2
H2C
but
CH3
CH2
H2C
CH3
Isoprene
2,3-dimethyl-1,3-butadiene
not 3-methylisoprene
Problem 1-5 Write IUPAC names of the following hydrocarbons
I
II
III
IV
6
2
1
V
3
4
6
5
5
7
3
4
2
1
3
I
II
4-ethyl-5-methyl-2-hexene
2,5-dimethyl-3-heptene
(or 4-ethyl-5-methylhex-2-ene) (or 2,5-dimethylhept-3-ene)
5
3
5
4
III
3-propyl-1,4-pentadiene
6
7
6
1
2
5
3
1
6
2
1
6
5
4
3
5
4
3
2
4
1
1
3
2
Nomenclature
of Organic Compounds
Chapter 1 11
I
II
III
4-ethyl-5-methyl-2-hexene
2,5-dimethyl-3-heptene
3-propyl-1,4-pentadiene
(or 4-ethyl-5-methylhex-2-ene) (or 2,5-dimethylhept-3-ene)
6
5
7
3 4
1
8
2
5
6
4
3
1
2
IV
V
3-ethyl-2-methyl-4-propyl-1,5-hexadiene 3-ethyl-6-methyl-2,6-octadiene
Problem 1-6 Write IUPAC names of the following hydrocarbons
I
II
III
IV
V
1
2
2
4
2
4
5
5
1
3
3
4
II
5-ethyl-5,6-dimethyl-2-heptyne
2
3
1
III
3-(1,2-dimethylpropyl)-1,5-hexadiyne
4
1
2
5
3
4
5
IV
3-(1-ethylpropyl)-1,4-pentadiyne
V
3-butyl-3-propyl-1,4-pentadiyne
Problem 1-7 Write IUPAC names of the following hydrocarbons
I
II
III
IV
6
7
5
V
2
4
3
1
I
5-hepten-1-yne
(or Hept-5-en-1-yne)
6
6
7
I
4.4-dimethyl-1-pentyne
5
3
1
2
1
4
3
6
5
II
1-hexen-5-yne
(or Hex-1-en-5-yne)
• Preference has gone to lower locant • Here both double bond and triple bonds are
number, not to triple bond.
equidistant from terminals, hence alphabetical
• When ‘ene’ follow ‘yne’, ‘e’ of ene is order is followed in numbering the parent chain.
elided and written as enyne.
12 Essential Organic Chemistry
2
1
4
3
8
6
5
III
1,3-heptadien-6-yne
4
6
9
7
7
2
8
1
3
5
9
4
6
7
2
3
5
1
V
8-nonene-1,3-diyne
(Here 'ene' is used because now
it follows consonent 'd')
IV
3,8-nonadien-1-yne
Problem 1-8 Write structural formulas of the following hydrocarbons
(I ) 3-ethyl-5-methyl-1,6-heptadiene.
(III ) 5-hepten-1-yne
(V ) 3,3-diethynyl-1,4-pentadiyne.
(II ) 3,4-diethyl-1,4-hexadiene.
(IV ) 4-ethenyl-3-ethyl-1,6-octadiene.
I
II
III
IV
V
Problem 1-9 Draw structures and write IUPAC name of all the alkenes with their molecular formula C5H10.
1-pentene
2-pentene
2-methyl-1-butene
3-methyl-1-butene
2-methyl-2-butene
Problem 1-10 Draw structures and write IUPAC name of all the alkynes with their molecular formula C5H8.
1-pentyne
2-pentyne
3-methyl-1-butyne
1-2E Naming Monocyclic Hydrocarbons
Rule 1 Name of monocyclic, saturated hydrocarbons are formed by attaching the prefix “cyclo” to the names of acyclic,
saturated hydrocarbon with same number of carbons
Cyclopropane Cyclopentane
Cyclohexane
Cyclo-octane
Rule 2 Name of unsaturated monocyclic hydrocarbons (with no side groups) is formed by substituting “-ene”, “-yne”,
“-adiene”, “-atriene”, “-adiyne” etc for “ane” in the name of corresponding cycloalkane eg,
1
5
Cyclohexene
1,3-cyclohexadiene
1
H3C
4
2
CH3
CH3
1,2,4-trimethylcyclohexene
H3C
H3C
4
1-cyclodecen-4-yne
3
2
1
4-ethyl-5-methylcyclohexene
3
2
3
4
1,4-cyclohexadiene
CH3
not
2
1
3-methylcyclohexene
1
H3 C
H3C
4
3
2
5-ethyl-4-methylcyclohexene
CH3
1
Cyclohexene
H3C
4
2
3
2
1
Nomenclature of4Organic Compounds Chapter 1 13
1,3-cyclohexadiene
1
3
2
5
1,4-cyclohexadiene
CH3
H3C
CH3
4
1-cyclodecen-4-yne
3
1
H3 C
not
1
H3C
1,2,4-trimethylcyclohexene
2
3-methylcyclohexene
4
H3C
4-ethyl-5-methylcyclohexene
3
2
5-ethyl-4-methylcyclohexene
If alkyl groups are equidistant from
double bond alphabetical order is
followed in numbering
CH3
1
H3C
3
4
H3C 5
2
CH3
4
1
1,3,5-trimethylcyclohexene
not 2,4,6-trimethylcyclohexene
3
2
5-methyl-1,3-cyclohexadiene
Rule 3 If a straight chain substituent attached to monocyclic hydrocarbon has greater number of carbon in the main
chain than the cyclic ring becomes substituent as
CH3 CH3
1
2 3 4
CH3
6
CH3
5
5
1
2
H3C
1-cyclopropyl-3-ethyl-2,4-dimethylhexane
3
4
CH2
1-cyclopentyl-3-ethyl-1,4-pentadiene
Problem 1-11 Write IUPAC names of the following substituted cyclic hydrocarbons
I
II
5
III
IV
Here numbering is done in alphabetical order because
all locants are equidistant from one another
1
3
5
I
3
3-methylcycloheptene
1
1-cyclopropyl-3-methyl-5-propyl cyclohexane
6
III
3
II
1-ethyl-3-isopropyl-5-methyl cyclohexane
1
V
3
1
IV
1-ethyl-6-isopropyl-3-methyl cyclodecane
V
Cyclopropylcyclopropane
14 Essential Organic Chemistry
Problem 1-12 Write IUPAC names of the following substituted cyclic hydrocarbons
I
II
III
IV
V
2
1
5
4
3
3
1
7
2
4
5
6
I
II
5-ethyl-1,2-dimethyl-1,3-cyclohexadiene
3,7-diethyl-1,4-cycloctadiene
2
1
4
3
1
2
III
IV
1,4-dicyclohexylcyclohexene
1,2,3-tricyclopropylcyclopropane
2
1
4
V
4-cyclohexylcyclopentene
Problem 1-13 Write IUPAC names of the following hydrocarbons
I
II
III
IV
1
3
2
4
I
II
2,3-dicyclopropyl-1,3-butadiene
2
1
3
2'
4
1'
Cyclohexylethyne
3'
3
2
4
1'
2'
1
III
4-(3-cyclopropylcyclopentyl)cyclohexene
IV
4-(2-cyclobutenyl)cyclohexene
Nomenclature of Organic Compounds Chapter 1 15
Problem 1-14 Draw structures of the following hydrocarbons
(I ) 3,3-dimethylcyclohexene
(III ) 4,5-diethyl-7-methyl cycloctene
(II ) 4-ethyl-6-methylcycloheptene
(IV ) 1,4-dicyclopentylcyclopentene
I
II
III
IV
1-2F Substituted Aromatic Hydrocarbons
Following names for the substituted monocyclic aromatic hydrocarbons are retained
H3C
CH3
CH2
CH3
CH3
Benzene
Cumene
CH3
CH3
Toluene
Styrene
CH3
CH3
CH3
o-xylene
m-xylene
CH3
H3C
CH3
p-xylene
H3C
CH3
Mesitylene
CH3
Cymene
Rule 1 Other monocyclic substituted hydrocarbons are named as derivatives of benzene or one of the compounds listed
above. However, if the substituent introduced into such a compound is identical with already present in that compound, then
the substituted compound is named as derivatives of benzene as
CH3
H2C
CH3
1,4-divinylbenzene
CH2
CH2
CH3
1-methyl-3-vinylbenzene
1,2,3-trimethylbenzene
Rule 2 The positions of substituents is indicated by numbers except o-(ortho), m-(meta), p-(para) may be used in place
of 1,2- , 1,3- , and 1,4-, respectively, when only two substituents are present. The lowest possible number given to the substituent coming 1st in alphabetical order except that when names are based on those of the compounds mentioned in the beginning
of section-E.
CH3
H3C
CH3
1-ethyl-4-pentylbenzene
H3C
1,4-dipropylbenzene
CH3
CH3
H2C
CH3
CH3
4-ethylstyrene p-ethylstyrene
CH3
1,2-dimethyl-3-propylbenzene
H3C
CH3
3,5-diethyltoluene
CH3
CH3
CH3
1-butyl-3-ethyl-2-propylbenzene
16 Essential Organic Chemistry
Problem 1-15 Write IUPAC names of the following hydrocarbons
I
II
III
IV
4
4
2
2
1
1
I
II
1,2,.4-trimethyl benzene
1,4-diisopropyl-2-propyl benzene
5
1
1
3
2
III
3
IV
1,3-diethyl-2,5-dimethyl benzene
1-cyclohexyl-3-cyclopentyl benzene
1-2G Naming Halogen Substituted Compounds
Substitutive naming of halogen compounds are formed by adding the prefixes “fluoro-“, “chloro-”, “bromo”- or “iodo”- to the
name of parent compound.
Cl
6
5
H3C
4
3
1
2
CH3
Cl
9
8
H3C
6
7
5 4
Cl
3-chlorohexane
3
2
1
Cl
8
CH3
H3C
7
6
Cl
5 4
3
2
1
CH3
Br
3,4,7-trichlorononane
5-bromo-2-chloroctane
If there is a choice between the two halides for numbering, alphabetical order is followed eg,
Br
Br
1
H3C
2
3
4
CH3
Cl
2-bromo-3-chlorobutane
6
I
1
2
3
5
4
4
F
1-bromo-3fluorocyclohexane
F
5
3
6
1
2
Cl
1-chloro-3-fluoro-5-iodocyclohexane
1-3 Naming Compounds Containing One or More
Similar Type of Principal Functional Groups
Name of such compound which contain principal functional group ends with suffix of that group provided by IUPAC.
Suffixes and prefixes for some of the common functional group is given in Table-1.2.
Nomenclature of Organic Compounds Chapter 1 17
Table 1.2 Suffixes and Prefixes for common functional groups
Class
Formula
Prefix
Suffix
(1) Acid halide
(2) Alcohols
—CO—X
—OH
Halocarbonyl
Hydroxy
Carbonyl halide
(3) Aldehydes
—CHO
—(C)HO
Formyl
Oxo-
(4) Amides
—CONH2
—(C)ONH2
Carbaldehyde
-al
Carbamoyl
Carboxamide
-amide
-amine
-ol
—NH2
—COOH
—(C)OOH
—OR
Amine
Carboxy
(8) Esters
—COOR
—(C)OOR
R-oxycarbonyl
R-carboxylate
R-oate
(9) Ketones
(C)==O
—CN
—(C)N
—SO3H
Oxo
-one
Cyano
-carbonitrile
nitrile
Sulpho
-Sulphonic acid
(5) Amines
(6) Carboxylic acid
(7) Ethers
(10) Nitrile
(11) Sulphonic acid
-carboxylic acid
-oic acid
Alkoxy
(Formulae containing carbon in parenthesis indicates that the carbon is part of main chain)
1-3A Aldehydes
Acyclic mono- and dialdehydes are named by adding suffix “-al” or “-dial” to the name of acyclic hydrocarbon with the
same number of carbon atoms, eliding the final “e” of the hydrocarbon name before “a”. Numbering starts from the carbon
of the aldehyde group —CHO.
H3C
1
CH3CHO
CHO
Ethanal
4
Pentanal
H3C
1
3
CHO
5
6
OHC
2
5
7
4
3
1
CHO
2
H3C
6
4-ethyl-2,5-heptadienal
2-ethylhexandial
If the parent chain contain more than two —CHO groups, they are named as carbaldehyde and carbon of —CHO is not
counted in main chain as
CHO
CHO
4
OHC
3
CHO
2
1
Butane-1,2,4-tricarbaldehyde
4
CHO
2
CHO
3
Cyclohexanecarbaldehyde
1
6
OHC
1
5
4
3
CHO
2
3-(formylmethyl) hexanedial
or 3-(2-oxoethyl) hexanedial
4-cyclopentylbutanal
1-3B Ketones
Ketones are named substitutively by adding a suffix such as “-one”, “-dione” etc to the name of parent hydrocarbon
CH3 CH3 O
O
O
5
H3C
4
3 2
2-pentanone
1
CH3
CH3
C6H5
O
1-phenylpentane-2,3-dione
7
H3C
6
5 4
3
2
1
CH3
O
4,6-dimethylhept-3-ene-2,5-dione