IUPAC Nomenclature IUPAC nomenclature uses the longest continuous chain of carbon atoms to determine the basic root name of the compound. The root name is then modified due to the presence of different functional groups which replace hydrogen or carbon atoms in the parent structure.

1. 1
Basic IUPAC Organic Nomenclature
IUPAC Nomenclature
IUPAC nomenclature uses the longest continuous chain of carbon atoms to determine
the basic root name of the compound. The root name is then modified due to the presence of
different functional groups which replace hydrogen or carbon atoms in the parent structure.
There are a number of different ways to modify the root name to indicate the functional groups
present.
 Substitutive : (most common) : the highest priority functional group modifies the
suffix of the root name, while all other groups, or substituents, are added as prefixes to
the root name.
 Functional group : names the compound based on the highest priority functional
group, i.e. as an alcohol, ketone, alkyl halide, etc.
 Replacement : used to indicate when an atom, usually carbon, is replaced by another
atom.
 Conjunctive : used to combine named subunits (i.e. cyclohexane carboxylic acid).
 Common or trivial : due to widespread use, some compounds with simple names have
been adopted into basic IUPAC nomenclature.
Remember:
 That organic molecules can in general be either chains (also known as acyclic) or cyclic
or a combination of both. In most cases this doesn't make a difference. The general rules
for cyclic systems will be developed for cycloalkanes and can be applied to other
scenarios.
 Molecules are not restricted to a single functional group, they can have several
functional groups. A common example are amino acids which have both an amine and a
carboxylic acid present.
Basic rules
The IUPAC systematic name of an organic compound can be constructed based on a series of
steps and rules:
 Identification of the principal functional group and substituents
 Identification of the longest continuous chain containing the principal functional group.
 Assign locants (i.e. numbering) to the principal functional group and substituents.
The steps and rules are summarized below, more details are provided as the cases are
encountered.

2. 2
Principal
Functional
group
 The principal functional group is used to define the class the compound
belongs to e.g. an alcohol, ROH
 The principal functional group is the highest priority functional group.
 The principal functional group is usually given the lowest locant possible.
 When a group is named as a substituent, the priority order does not apply.
Longest chain  The longest continuous chain containing the principal functional
group defines the root name.
 Other groups attached to this chain are called substituents.
 If there are two chains of equal length, then the choice that gives the
simplest substituents is chosen.
Numbering
(i.e. assigning
locants)
 The numbers that define the positions of the principal functional group and
substituents are called locants.
 Compounds are numbered from one end of the longest continuous chain.
 The locants are assigned such that the principal functional group gets
the lowest possible locant.
 If this results in a "tie" then the first point of difference rule is applied so that
the first time a difference in numbering occurs, then the method that gives the
lower number at this first difference is used.
 In the event that there is no first point of difference then alphabetisation is
used.
 Note that a locant can only be omitted if they are a. "1" and b. would be
unambiguous (see later).
First point of Difference Rule
This is probably the most difficult of the rules associated with nomenclature to
master.
The factors that influence the numbering according to the first point of difference
rule are:
1. The principal functional group is given the lowest possible locant.
2. Substituents are then assigned locants based on this numbering scheme in such
a way as to give the lowest locant number at the first time there is a difference.
3. In the event that there is no first point of difference in the locants, substituents
are numbered based on alphabetization giving the first substituent the lowest
possible locant number.

3. 3
Alkanes
Nomenclature Formula
Functional group suffix = -ane
Substituent name = alkyl
Structural unit : alkanes contain only C-C and C-H bonds.
Note: alkanes are the simplest organic compounds and are
the minimum present in an organic molecule.
 Simple alkane chains without branches are named using the appropriate root
name plus the suffix -ane:
Propane
CH3CH2CH3
 Simple cyclic alkanes without branches are named using the prefix cyclo plus
the appropriate root name plus the suffix -ane:
Cyclopropane
Alkenes
Nomenclature Formula
Functional group suffix = -ene
Substituent name = alkenyl
Structural unit : alkenes contain C=C bonds.
 The root name is based on the longest chain containing both ends of the alkene unit, the
C=C.
 The chain is numbered so as to give the alkene unit the lowest possible numbers.
 The locant for the first carbon of the alkene is used in the name.
 If the position of the alkene is unambiguous, the locant is not required, see
examples below.
 As we will see later, in certain cases we will also need to specify the stereochemistry.
We are going to ignore stereochemistry on this page to deal with the basics first.

4. 4
 Functional group is an alkene, therefore suffix = -ene
 The longest continuous chain is C3 therefore root = prop
 In order to give the alkene the lowest number, number from
the right as drawn
The C=C is unambiguously between C1 and C2 therefore the locant isn't
required
CH3CH=CH2
Propene
 Functional group is an alkene, therefore suffix = -ene
 The longest continuous chain is C4 therefore root = but
The C=C is between C2 and C3 so the locant is 2-
CH3CH=CHCH3
but-2-ene or 2-butene
 Functional group is an alkene, therefore suffix = -ene
 The longest continuous chain is C4 therefore root = but
 In order to give the alkene the lowest number, number from
the right as drawn
The C=C is between C1 and C2 so the locant is 1-
CH3CH2CH=CH2
but-1-ene or 1-butene
 Functional group is an alkene, therefore suffix = -ene
 The longest continuous chain is C6 therefore root = hex
 The system is cyclic there prefix = cyclo
The C=C is unambiguously between C1 and C2 therefore the locant isn't
required. Cyclohexene
 Functional group is an alkene, therefore suffix = -ene
 The longest continuous chain is C5 therefore root = pent
 In order to give the alkene the lowest number, number from
the right as drawn
 The C=C is between C2 and C3 so the locant is 2-
 The substituent is a C1 alkyl group i.e. a methyl group
The methyl group locant is 4-
4-methylpent-2-ene or 4-
methyl-2-pentene
 Functional group is an alkene, therefore suffix = -ene
 The longest continuous chain is C6 therefore root = hex
 The C=C is between C3 and C4 so the locant is 3-
 The substituent is a C1 alkyl group i.e. a methyl group
 The first point of difference rule requires numbering from
the right as drawn to make the methyl group locant 3-
3-methylhex-3-ene or 3-
methyl-3-hexene

5. 5
Alkynes
Nomenclature Formula
Functional group suffix = -yne
Substituent prefix = alkynyl
Structural unit : alkynes contain C≡C bonds.
 The root name is based on the longest chain containing both ends of the alkyne unit, the
C≡C.
 The chain is numbered so as to give the alkyne unit the lowest possible number.
 Functional group is an alkyne, therefore suffix = -yne
 The longest continuous chain is C4 therefore root = but
 The first point of difference rule requires numbering from the right as drawn,
the substituent locant is 1-
but-1-yne or 1-butyne
CH3CH2C≡CH
 Functional group is an alkyne, therefore suffix = -yne
 The longest continuous chain is C4 therefore root = but
 The substituent is a C2 alkyl group i.e. a ethyl group
 The first point of difference rule requires numbering from the right as drawn,
the substituent locant is 2-
but-2-yne or 2-butyne
CH3C≡CCH3
Haloalkanes / Alkyl halides
Nomenclature Formula
Functional group suffix = halide (i.e. fluoride, chloride, bromide, iodide)
Substituent name = halo- (i.e. fluoro, chloro, bromo, iodo)
Structural unit : haloalkanes contain R-X where X = F, Cl, Br, I etc.
Notes :
 Haloalkanes can also be named as alkyl halides despite the fact that the
halogens are higher priority than alkanes.
 The alkyl halide nomenclature is most common when the alkyl group is
simple.

6. 6
Halo alkane
 The root name is based on the longest chain containing the halogen.
 This root give the alkane part of the name.
 The type of halogen defines the halo prefix, e.g. chloro-
 The chain is numbered so as to give the halogen the lowest possible number
Alkyl-halide
The root name is based on the longest chain containing the halogen.
 This root give the alkyl part of the name.
 The type of halogen defines the halide suffix, e.g. chloride
 The chain is numbered so as to give the halogen the lowest possible number.
Haloalkane style:
 Functional group is an alkane, therefore suffix = -ane
 The longest continuous chain is C2 therefore root = eth
 The substituent is a bromine, therefore prefix = bromo
 No locant is required since the -Br location is unambiguous (i.e. substitution
at either carbon gives the same molecule)
CH3CH2Br
Alcohols
Nomenclature
Formula
Functional class name = alkyl alcohol e.g. ethyl alcohol
Substituent suffix = -ol e.g. ethanol
Substituent prefix = hydroxy- e.g. hydroxyethane
Structural unit : alcohols contain R-OH
 The root name is based on the longest chain with the -OH attached.
 The chain is numbered so as to give the alcohol unit the lowest possible number.
 The alcohol suffix is appended after the hydrocarbon suffix minus the "e" : e.g. -ane + -
ol = -anol or -ene + ol = -enol.

7. 7
 Functional group is an alcohol, therefore suffix = -ol
 Hydrocarbon structure is an alkane therefore -ane
 The longest continuous chain is C2 therefore root = eth
 No locant is required since the -OH location is unambiguous (i.e.
substitution at either carbon gives the same molecule)
Ethanol
CH3CH2OH
 Functional group is an alcohol, therefore suffix = -ol
 Hydrocarbon structure is an alkane therefore -ane
 The longest continuous chain is C3 therefore root = prop
 It doesn't matter which end we number from, the alcohol group locant
is 2-
propan-2-ol or 2-propanol
(or isopropanol)
CH3CH(OH)CH3
Ethers
Nomenclature Formula
Functional class name = alkyl alkyl ether e.g. ethyl
methyl ether
Substituent prefix = alkoxy- e.g. methoxyethane
Simple" ethers
 If both groups are simple alkyl groups, then the ether is usually named as alkyl alkyl
ether
 The alkyl groups are listed in alphabetical order
 If the two alkyl groups are the same, then it's a dialkyl ether
 Functional group is a simple ether, therefore use alkyl alkyl ether
 First substituent is C1 alkane therefore alkyl = methyl
 Second substituent is C2 alkane therefore alkyl = ethyl
ethyl methyl ether
CH3CH2OCH3
 Functional group is a simple ether, therefore use alkyl alkyl ether
 Both substituents are C2 alkane therefore alkyl = ethyl
 Since there are two alkyl groups, multipler = di
CH3CH2OCH2CH3

8. 8
diethyl ether
Amines
Nomenclature Formula
Functional class name = alkylamines or alkanamines
Substituent suffix = -amine e.g. ethylamine
Substituent prefix = amino- e.g. aminoethane
Structural unit (depending on R, R' and R")
 primary amines contain R-NH2
 secondary amines contain R2NH
 tertiary amines contain R3N.
There are slight differences between amines depending on whether they are primary,
secondary or tertiary (based on number of R groups attached to the N)

9. 9
Aldehydes
Nomenclature Formula
Functional class name = ?
Substituent suffix = -al e.g. ethanal
Substituent prefix = oxo-
 The root name is based on the longest chain including the carbonyl group.
 Since the aldehyde is at the end of the chain, it must be C1.
 The aldehyde suffix is appended after the hydrocarbon suffix minus the "e" : e.g. -ane +
-al = -anal or -ene + al = -enal etc.
 Functional group is an aldehyde, therefore suffix = -al
 Hydrocarbon structure is an alkane therefore -ane
 The longest continuous chain is C3 therefore root = prop
propanal CH3CH2CHO
Ketones
Nomenclature Formula
Functional class name = alkyl alkyl ketone
Substituent suffix = -one e.g. propan-2-one
Substituent prefix = oxo-
 The root name is based on the longest chain including the carbonyl group.
 The chain is numbered so as to give the ketone carbonyl the lowest possible number.
 The ketone suffix is appended after the hydrocarbon suffix minus the "e" : e.g. -ane + -
one = -anone or -ene + one = -enone etc.
 Functional group is a ketone, therefore suffix = -one
 Hydrocarbon structure is an alkane therefore -ane
 The longest continuous chain is C5 therefore root = pent
 The first point of difference rule requires numbering from
CH3CH2CH2C(=O)CH3

10. 10
the left as drawn to make the ketone group locant 2-
pentan-2-one or 2-pentanone
Carboxylic Acids
Nomenclature Formula
Substituent suffix = -oic acid e.g. ethanoic acid
Substituent prefix = carboxy
 The root name is based on the longest chain including the carboxylic acid group.
 Since the carboxylic acid group is at the end of the chain, it must be C1.
 The carboxylic acid suffix is appended after the hydrocarbon suffix minus the "e"
: e.g. -ane + -oic acid = -anoic acid etc.
 Functional group is a carboxylic acid, therefore suffix = -oic acid
 Hydrocarbon structure is an alkane therefore -ane
 The longest continuous chain is C4 therefore root = but
butanoic acid
CH3CH2CH2C(=O)OH
Esters
Nomenclature Formula
Functional class name = alkyl alkanoate
Substituent suffix = -oate
 Esters are alkyl derivatives of carboxylic acids.
 The easiest way to deal with naming esters is to recognise the carboxylic acid and the
alcohol that they can be prepared from.
 The general ester, RCO2R' can be derived from the carboxylic acid RCO2H and the
alcohol R'OH.
 The first component of an ester name, the alkyl is derived from the alcohol, R'OH
portion of the structure.
 The second component of an ester name, the -oate is derived from the carboxylic acid,
RCO2H portion of the structure.

11. 11
 Alcohol component
o The root name is based on the longest chain containing the -OH group.
o The chain is numbered so as to give the -OH the lowest possible number.
 Carboxylic acid component
o The root name is based on the longest chain including the carbonyl group.
o Since the carboxylic acid group is at the end of the chain, it must be C1.
o The ester suffix for the acid component is appended after the hydrocarbon suffix
minus the "e" : e.g. -ane + -oate = -anoate etc.
 The complete ester name is the alkyl alkanoate
 Functional group is an ester, therefore suffix = -oate
 The alcohol component here is methanol, so the alkyl = methyl
 The acid component here is propanoic acid, so propanoate
methyl propanoate
Amides
Nomenclature Formula
Functional class name = alkyl alkanamide
Substituent suffix = -amide
 Amides are amine derivatives of carboxylic acids.
 The root name is based on the longest chain including the carbonyl group of the amide
group.
 Since the amide group is at the end of the chain, the C=O carbon must be C1.
 The amide suffix is appended after the hydrocarbon suffix minus the "e" : e.g. -ane + -
amide = -anamide etc.
 If the amide nitrogen is substituted, the these substituents are given N- as the locant.
 The N- locant is listed first when the same substituent occurs on N and other
locations, e.g. N,2-dimethyl
 Functional group is an amide therefore suffix = -amide
 Hydrocarbon structure is an alkane therefore -an-
 The longest continuous chain is C4 therefore root = but
butanamide

12. 12
CH3CH2CH2C(=O)NH2

13. 13
Nitriles
Nomenclature Formula
Functional class = alkyl cyanide
Functional group suffix = nitrile or -onitrile
Substituent prefix = cyano-
Notes :
 The cyano prefix is used in a very similar manner to haloalkanes
 The cyano nomenclature is most common when the alkyl group is simple.
 The nitrile suffix is used in a very similar manner to carboxylic acids.
Cyano substituent style:
The root name is based on the longest chain with the -C≡N as a substituent.
 This root give the alkane part of the name.
 The chain is numbered so as to give the -C≡N group the lowest possible locant number
Cyano substituent style:
 Functional group is an alkane, therefore suffix = -ane
 The longest continuous chain is C3 therefore root = prop
 The substituent is a -CN therefore prefix = cyano
 The first point of difference rule requires numbering from the right as drawn,
the substituent locant is 1-
1-cyanopropane
CH3CH2CH2C≡N
Benzene
Benzene is an important structure.
It's the most common aromatic hydrocarbon.
Since benzene (and its relatives) have their own characteristic reactions, they
are a functional group, often referrred to as arenes C6H6

14. 14
 In principle, all the substituents we have encountered can occur as substituents on
benzene rings.
 One way to name these is to use the benzene as the root and add the approriate
substituent prefix.
 Hydrocarbon structure is benzene
 The substituent is a bromine therefore = bromo
Bromobenzene
C6H5Br