The document discusses the classification, nomenclature, and structural isomerism of organic compounds. It describes how organic compounds can be classified as acyclic, alicyclic, aromatic, and heterocyclic. The IUPAC system of nomenclature is also outlined, including rules for naming parent chains, substituents, and complex groups. Finally, different types of structural isomerism are defined, such as chain, position, functional, metamerism, tautomerism, and ring-chain isomerism.

1. Classification, nomenclature and
isomerism of organic compounds
Unit – 1 POC - 1
B. Pharmacy (Credit system-
Syllabus wise)

2. Contents
1. Classification of Organic Compounds
2. Common and IUPAC systems of nomenclature of
organic compounds
3. Structural isomerisms in organic compounds
2
PHARMA EXPRESS

3. 1. Classification of Organic Compounds
• The compounds in solid, liquid or gaseous state
which contain carbon in its molecule are known as
organic compounds.
• There are a large number of organic compounds and
therefore a proper systematic classification was
required.
• Organic compounds can be broadly classified as
acyclic (open chain) or cyclic (closed chain)
3
PHARMA EXPRESS

4. PHARMA EXPRESS
4

5. A) Acyclic or Open Chain Compounds:
These compounds are also known as aliphatic compounds, they have branched
or straight chains. Following are the examples in this category.
PHARMA EXPRESS
5

6. B) Alicyclic or Closed Chain or Ring Compounds:
These are cyclic compounds which contain carbon atoms connected to each
other in a ring (homocyclic). When atoms other than carbon are also present
then it is called as heterocyclic. Examples of this type are as follows:
PHARMA EXPRESS
6

7. C) Aromatic Compounds
They are a special type of compounds which contain benzene and other ring related
compounds. Similar to alicyclic, they can also have heteroatoms in the ring. Such
compounds are called heterocyclic aromatic compounds. Some examples are as
follows:
PHARMA EXPRESS
7
a) Benzenoid aromatic compounds

8. b) Non-benzenoid aromatic compounds
PHARMA EXPRESS
8

9. D. Heterocyclic Aromatic Compounds
PHARMA EXPRESS
9

10. 2. IUPAC Nomenclature
• IUPAC nomenclature of organic compounds refers to
the systematic approach taken for the nomenclature of organic
compounds as per the recommendation of the International
Union of Pure and Applied Chemistry (often abbreviated to
IUPAC).
• The necessity for such a systematic approach arose due to the sheer
quantity of new discoveries of organic compounds which made the
trivial nomenclature of organic compounds highly inconvenient
• Trivial Nomenclature System-
The Trivial Nomenclature system involves a non-systematic
approach to the naming of organic compounds.
Example- tartaric acid -- 2,3-dihydroxy-1,4-Butanedioic acid.
PHARMA EXPRESS
10

11. IUPAC Nomenclature Guidelines
• The Longest Chain Rule: The parent hydrocarbon must be
identified and subsequently named. The parent chain belonging to
the compound in question is generally the longest chain of carbon
atoms, be it in the form of a straight chain or a chain of any other
shape
• The Lowest Set of Locants: The carbon atoms belonging to the
parent hydrocarbon chain must be numbered using natural
numbers and beginning from the end in which the lowest number is
assigned to the carbon atom which carries the substituents.
• Multiple instances of the same substituent: Prefixes which
indicate the total number of the same substituent in the given
organic compounds are given, such as di, tri, etc.
• Naming of different substituents: In the organic compounds
containing multiple substituents, the corresponding substituents are
arranged in alphabetical order of names in the IUPAC nomenclature
of organic compounds in question.
PHARMA EXPRESS
11

12. • The naming of different substituents present at the same
positions: In the scenario wherein two differing substituent groups
are present at the same position of the organic compound, the
substituents are named in ascending alphabetical order.
• Naming Complex Substituents: Complex substituents of
organic compounds having branched structures must be named as
substituted alkyl groups whereas the carbon which is attached to the
substituent group is numbered as one. These branched and complex
substituents must be written in brackets in the IUPAC nomenclature
of the corresponding compounds.
• Locant + Prefix + Root + Locant + Suffix
PHARMA EXPRESS
12

13. 3. Structural isomerisms in organic compounds
• Isomerism is the phenomenon in which more than one compounds have the
same chemical formula but different chemical structures.
PHARMA EXPRESS
13
• Structural isomerism is commonly referred to as constitutional isomerism.
The functional groups and the atoms in the molecules of these isomers are
linked in different ways. Different structural isomers are assigned different
IUPAC names since they may or may not contain the same functional group.

14. Chain Isomerism
• It is also known as skeletal isomerism.
• The components of these isomers display differently branched
structures.
• Commonly, chain isomers differ in the branching of carbon
• An example of chain isomerism can be observed in the compound
C5H12, as illustrated below.
PHARMA EXPRESS
14

15. Position Isomerism
• The positions of the functional groups or substituent
atoms are different in position isomers.
• Typically, this isomerism involves the attachment of the
functional groups to different carbon atoms in the
carbon chain.
• An example of this type of isomerism can be observed in
the compounds having the formula C3H7Cl.
PHARMA EXPRESS
15

16. Functional Isomerism
• It is also known as functional group isomerism.
• As the name suggests, it refers to the compounds that
have the same chemical formula but different functional
groups attached to them.
• An example of functional isomerism can be observed in
the compound C3H6O
PHARMA EXPRESS
16

17. • Metamerism
• This type of isomerism arises due to the presence of different
alkyl chains on each side of the functional group.
• It is a rare type of isomerism and is generally limited to
molecules that contain a divalent atom (such as sulfur or
oxygen), surrounded by alkyl groups.
• Example: C4H10O can be represented as ethoxyethane
(C2H5OC2H5) and methoxy-propane (CH3OC3H7).
• Tautomerism
• A tautomer of a compound refers to the isomer of the
compound which only differs in the position of protons and
electrons.
• Typically, the tautomers of a compound exist together in
equilibrium and easily interchange.
• It occurs via an intramolecular proton transfer.
• An important example of this phenomenon is Keto-enol
tautomerism.
PHARMA EXPRESS
17

18. Ring-Chain Isomerism
• In ring-chain isomerism, one of the isomers has an open-
chain structure whereas the other has a ring structure.
• They generally contain a different number of pi bonds.
• A great example of this type of isomerism can be
observed in C3H6. Propene and cyclopropane are the
resulting isomers, as illustrated below.
PHARMA EXPRESS
18

19. Thank You
PHARMA EXPRESS
19