Chapter 2

ORGANIC CHEMISTRY
Chapter two
Nomenclature of organic compounds
1 Organic Chemistry 5-Nov-21

Cont’d
 Nomenclature in organic chemistry is of two types:
 Common names: The older names for organic compounds and
 Systematic (IUPAC rule): The formal system of nomenclature for
organic compounds.
 Some common names existed long before organic chemistry became an
organized branch of chemical science.
 Methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane,
and neopentane are common names.

 But there are millions of organic compounds already known.
 Now IUPAC rules was built.
 IUPAC = “International Union of Pure and Applied Chemistry.”

Some general rules remembered when naming organic compounds:
 The longest unbranched chain containing the functional group is the
parent molecule or simply the longest unbranched chain for alkanes.
 Indicate the position of the functional group with a number, numbering
from the end nearest the functional group.
 Name the branches and indicate the number of branches.
 Indicate the position of the branches with a number, numbering from the
end nearest the functional group.
 If there is more than one branch, the branches are identified in
alphabetical order.
 Each branch needs to be numbered individually, even if they are
attached to the same carbon atom.
 The rule is a comma between numbers and a dash between numbers and
letters.
Nomenclature of Alkanes
 The alkanes are hydrocarbons with the general formula CnH2n+2
 The IUPAC rules assign names to unbranched alkanes as
 Methane, CH4,
 Ethane, CH3CH3,
 Propane, CH3CH2CH3,
 Butane, CH3CH2CH2CH3,
 Pentane, CH3CH2CH2CH2CH3,
 Hexane, CH3CH2CH2CH2CH2CH3,
 Heptane, CH3CH2CH2CH2CH2CH2CH3,
 Octane, CH3CH2CH2CH2CH2CH2CH2CH3,
 Nonane, CH3CH2CH2CH2CH2CH2CH2CH2CH3,
 Decane, CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Naming alkanes according to IUPAC rules
Step 1. Find the parent hydrocarbon – that means find the longest continuous carbon chain in the
molecule:
hex ane hept ane dec ane
If 2 different chains are equal, choose the one with the larger number of branch points:
NOT
hexane with 2 substituents hexane with 1 substituent

Step 2. Number the atoms in the main chain beginning at the end nearer the first branch
point:
2 6 6 2
4 4
1 3 5 7 NOT 7 5 3 1
If there is branching equal distance away from both ends, begin numbering at the end
nearer the second branch point:
2 6 8 8 4 2
4 6
1 3 5 7 9 NOT 9 7 5 3 1

Step 3. Identify and number the substituents:
2 6 8
4
1 3 5 7 9 4 6
2
1 3 5
on C3, CH2CH3 (3-ethyl) on C2, CH3 (2-methyl)

on C4, CH3 (4-methyl) on C4, CH3 (4-methyl)
on C7, CH3 (7-methyl) on C4, CH2CH3 (4-ethyl)
3-ethyl-4,7-dimethylnonane 4-ethyl-2,4-dimethylhexane
Step 4. Write the name as a single word using hyphen to separate different prefixes, and
commas to separate numbers. Prefixes should appear in alphabetical order.

ALKYL GROUPS
 An alkyl group lacks one of the hydrogen substituents of an alkane.
 A methyl group (CH3-) is an alkyl group derived from methane (CH4).
 Unbranched alkyl groups in which the point of attachment is at the end of

the chain are named in IUPAC nomenclature by replacing the -ane endings
of alkanes by -yl.
 The dash at the end of the chain represents a potential point of attachment
for some other atom or group.

Alkenes
The IUPAC rules for naming alkenes are similar in many respects to those
for naming alkanes:
1. Determine the parent name by selecting the longest chain that contains
the double bond and change the ending of the name of the alkane of
identical length from –ane to -ene.
Example, if the longest chain contains five carbon atoms, the parent name
for the alkene is pentene; if it contains six carbon atoms, the parent name is
hexene, and so on.
2. Number the chain so as to include both carbon atoms of the double bond,
and begin numbering at the end of the chain nearer the double bond.

3. Indicate the locations of the substituent groups by the
numbers of the carbon atoms to which they are attached:

Alkynes
 Alkynes are named in much the same way as alkanes.
 Unbranched alkynes, for example, are named by replacing the -ane
of the name of the corresponding alkane with the ending -yne.
 The chain is numbered to give the carbon atoms of the triple bond
the lower possible numbers.
 The lower number of the two carbon atoms of the triple bond is used
to designate the location of the triple bond.

 The locations of substituent groups of branched alkynes and
substituted alkynes are also indicated with numbers.
 -OH group has priority over the triple bond and double bond
when numbering the chain of an alkynol:

Alcohols
 The following rules are used to name a compound that has a
functional group suffix:
1. Select the longest continuous carbon chain to which the hydroxyl is
directly attached.
Change the name of the alkane corresponding to this chain by
dropping the final –e and adding the suffix -ol.
2. The parent hydrocarbon is numbered in the direction that gives the
functional group suffix the lowest possible number.

3. If there is a functional group suffix and a substituent, the functional
group suffix gets the lowest possible number.
4. If the same number for the functional group suffix is obtained in

both directions, the chain is numbered in the direction that gives a
substituent the lowest possible number.

5. If there is more than one substituent, the substituents are
cited in alphabetical order.

Aromatics
 Determining the root name of the parent ring; determining priority,
name, and position number of substituents; and assembling the

name in alphabetical order.
 Some monosubstituted benzenes are named simply by stating the
name of the substituent, followed by the word “benzene.”

 When two substituents are present, their relative positions are
indicated by the prefixes ortho-, meta-, and para-(abbreviated o-, m-,
and p-) or by the use of numbers.
 If more than two groups are present on the benzene ring, their
positions must be indicated by the use of numbers.

Aldehydes =
 Aliphatic aldehydes are named in the IUPAC system by replacing the final -
e of the name of the corresponding alkane with -al.
 Since the aldehyde group must be at an end of the carbon chain, there
is no need to indicate its position.
 When other substituents are present the carbonyl group carbon is assigned
position 1.
 Aldehydes in which the −CHO group is attached to a ring system are

named by adding the suffix carbaldehyde.

Ketones=
 Aliphatic ketones are named by replacing the final -e of the name of
the corresponding alkane with -one.
 The chain is then numbered in the way that gives the carbonyl carbon
atom the lower possible number, and this number is used to designate
its position.

Amines (RNH2)
The IUPAC system for naming amines is as follows:
 Select the longest carbon chain bound to the nitrogen as the parent chain
 Name the chain by changing the alkane name for this chain: drop the
“e” and add “amine”

 Number the chain to give the nitrogen the lowest numbering
 The number and identity of other substituents (including any on the
main chain) are indicated at the beginning of the amine name (some are
attached to N)
 Amines are classified as being primary, secondary, or tertiary on the
basis of the number of organic groups attached to the nitrogen.

 In systematic nomenclature primary (1°) amines are named
by adding the suffix -amine to the name of the chain or ring

system to which the NH2 group is attached with replacement
of the final -e.
Primary Amines

 Secondary and tertiary amines are named in the systematic
nomenclature by using the locant N to designate substituents attached
to a nitrogen atom. The longest alkane will be the parent name.
Secondary Amines
Tertiary Amines

Ethers (R-O-R’)
 Ethers are named in two ways:
 Common name - Name(s) of alkyl group(s) listed in alphabetical
order first followed by the word “ether”
 When both alkyl groups are the same, the prefix di- precedes
the name of the alkyl group.
 IUPAC name: The smaller alkyl group is converted to an “alkoxy”

name and used as a substituent then name of the alkanes.


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ORGANIC CHEMISTRY

1 Organic Chemistry 5-Nov-21

 Common names: The older names for organic compounds and

 Systematic (IUPAC rule): The formal system of nomenclature for

and neopentane are common names.

 Now IUPAC rules was built.

 IUPAC = “International Union of Pure and Applied Chemistry.”

2 Organic Chemistry 5-Nov-21

4 Organic Chemistry 5-Nov-21

hex ane hept ane dec ane

hexane with 2 substituents hexane with 1 substituent

5 Organic Chemistry 5-Nov-21

6 Organic Chemistry 5-Nov-21

on C3, CH2CH3 (3-ethyl) on C2, CH3 (2-methyl)

7 Organic Chemistry 5-Nov-21

 A methyl group (CH3-) is an alkyl group derived from methane (CH4).

 Unbranched alkyl groups in which the point of attachment is at the end of

8 Organic Chemistry 5-Nov-21

9 Organic Chemistry 5-Nov-21

10 Organic Chemistry 5-Nov-21

 Unbranched alkynes, for example, are named by replacing the -ane

of the name of the corresponding alkane with the ending -yne.

the lower possible numbers.

to designate the location of the triple bond.

11 Organic Chemistry 5-Nov-21

substituted alkynes are also indicated with numbers.

when numbering the chain of an alkynol:

12 Organic Chemistry 5-Nov-21

13 Organic Chemistry 5-Nov-21

4. If the same number for the functional group suffix is obtained in

14 Organic Chemistry 5-Nov-21

15 Organic Chemistry 5-Nov-21

 Determining the root name of the parent ring; determining priority,

name, and position number of substituents; and assembling the

 Some monosubstituted benzenes are named simply by stating the

name of the substituent, followed by the word “benzene.”

16 Organic Chemistry 5-Nov-21

17 Organic Chemistry 5-Nov-21

 Aldehydes in which the −CHO group is attached to a ring system are

18 Organic Chemistry 5-Nov-21

19 Organic Chemistry 5-Nov-21

“e” and add “amine”

 The number and identity of other substituents (including any on the

 Amines are classified as being primary, secondary, or tertiary on the

basis of the number of organic groups attached to the nitrogen.

20 Organic Chemistry 5-Nov-21

by adding the suffix -amine to the name of the chain or ring

21 Organic Chemistry 5-Nov-21

22 Organic Chemistry 5-Nov-21

 IUPAC name: The smaller alkyl group is converted to an “alkoxy”

23 Organic Chemistry 5-Nov-21

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