This document provides information on the classification, nomenclature, and isomerism of organic compounds. It discusses the classification of organic compounds as acyclic, cyclic, alicyclic, aromatic, heterocyclic, and more. It also covers IUPAC nomenclature rules for naming alkanes, alkenes, alkynes, alkyl halides, alcohols, aldehydes, ketones, carboxylic acids, esters, and ethers. Examples are provided to illustrate the nomenclature rules for different functional groups. Structural isomerism in organic compounds is also briefly mentioned.

1. SARASWATI GROUP OF
COLLEGE OF PHARMACY
B PHARMA II SEMESTER
PHARMACEUTICAL ORGANIC CHEMISTRY –I
ASSISTANT PROFFESOR SALONI SAINI

2. UNIT-I
Classification , Nomenclature and Isomerism
 Classification of Organic compounds
 Common and IUPAC systems of nomenclature
of organic compounds (up to 10 Carbons open
chain and carboxylic compounds)
 Structural Isomerism in organic compounds

3. Classification ,Nomenclature and
Isomerism
• An Organic compound is generally any
chemical compound that contains carbons.
• Due to carbon’s ability to form chains with
other carbons atoms millions of organic
compounds are known.
• Study of the properties and synthesis of
organic compounds is known as organic
chemistry.

4. Based upon structure they are classified into
two types
 Acyclic compounds ( open chain)
 Cyclic compounds( closed chain)

5. Classification of organic compounds

6. Acyclic (or) open chain compounds:
• These compounds contains open chain of carbon atoms
in their molecules.
• The terminal carbon atom are completely free they are
not linked with each other.
• The chain is open so ,it is called open chain compound.
Ex: CH3-CH2-CH2-CH2-CH3 pentane
Free terminal carbon atom –CH3-CH2-CH3-
:CH3-CH2-CH2-CH2-CH2-CH3 hexane
:CH3-COOH acetic acid

7. Cyclic (or) closed chain compounds:
• These compounds contain one (or) more closed
chains (or) rings of atoms in their molecules.
• In this case two terminal carbon atoms are linked
with each other. In order to form a closed ring.
• It can be either a three, four, five membered rings.

8. • Homocyclic or carbocyclic: These are the compounds
having a ring or rings of carbon atoms only in the
molecules. The carbocyclic or homocyclic compounds
may again be divided into two types:
• Alicyclic compounds: These are the compounds which
contains rings of three or more carbon atoms.
• These resembles with aliphatic compounds in many
respects.
• That is why these are named alicyclic, i.e., aliphatic
cyclic. These are also termed as polymethylenes. Some
of the examples are,

9. • Aromatic compounds: These compounds consist
of at least one benzene ring, i.e., a six- membered
carbocyclic ring having alternate single and
double bonds.
• Generally, these compounds have some fragrant
odour and hence, named as Aromatic (Greek word
aroma means sweet smell).
• These compounds may again be divided into two
types:
 Monocyclic aromatic ring compounds
Polycyclic aromatic ring compounds
• These are also called benzenoid aromatics.

11. Non-benzenoid aromatics : These are aromatics compounds,
which have structural units different from benzenoid type and
are known as Non-benzenoid aromatics e.g. Tropolone ,
azulene etc.
Heterocyclic compounds: Cyclic compounds containing one or
more hetero atoms (e.g. O, N, S etc.) in the ring are called
haterocyclic compounds.

12. Alicyclic heterocyclic compounds: Heterocyclic
compounds which resembles aliphatic
compounds in their properties are called
alicyclic heterocyclic compounds.

13. Aromatic heterocyclic compounds: Heterocyclic
compounds which resembles benzene in most of
their properties are called aromatic heterocyclic
compounds .For example,

14. Classification of organic compounds based on
functional groups
• A functional group is an atom or group of atoms
in a molecule that gives the molecules its
characteristics chemical properties, double and
triple bonds are also considered as functional
groups.
• All compounds with the same functional group
belong to the same class.
• Various classes of compounds having some of the
common functional groups are listed in the table.

16. Nomenclature in organic chemistry
 It is important that organic compounds are
correctly and unambiguously named so that there
can be absolutely no confusion about what
compounds are actually being reported or
described.
 There have been many conventions for naming
organic compounds. The International Union of
Pure and Applied Chemistry (I.U.P.A.C)
periodically reviews naming practice, attempting
to standardise nomenclature.

17.  The following guidelines for organic
nomenclature are based on the definitive
rules published by I.U.P.A.C (the International
Union of Pure and Applied Chemistry).
I.U.P.A.C. Nomenlcature of Alkanes
(saturatedhydrocarbons)
The names of straight chain saturated
hydrocarbons for up to a 10 carbon chain are
shown below.

18. Number of carbons Name
1 methane
2 ethane
3 propane
4 butane
5 pentane
6 hexane
7 heptane
8 octane
9 nonane
10 decane

20. • There are a few common branched
substituents which you should memorize.
These are shown below.

21. • Identify the longest carbon chain. This chain is
called the parent chain.
• Identify all of the substituents (groups appending
from the parent chain).
• Number the carbons of the parent chain from the
end that gives the substituents the lowest
numbers. When compairing a series of numbers,
the series that is the "lowest" is the one which
contains the lowest number at the occasion of
the first difference. If two or more side chains are
in equivalent positions, assign the lowest number
to the one which will come first in the name.

22. • If the same substituent occurs more than once,
the location of each point on which the
substituent occurs is given. In addition, the
number of times the substituent group occurs is
indicated by a prefix (di, tri, tetra, etc.).
• If there are two or more different substituents
they are listed in alphabetical order using the
base name (ignore the prefixes). The only prefix
which is used when putting the substituents in
alphabetical order is iso as in isopropyl or
isobutyl. The prefixes sec- and tert- are not used
in determining alphabetical order except when
compared with each other.

23.  If chains of equal length are competing for
selection as the parent chain, then the choice
goes in series to:
a) the chain which has the greatest number of
side chains.
b) the chain whose substituents have the
lowest- numbers.
c) the chain having the greatest number of
carbon atoms in the smaller side chain.
d)the chain having the least branched side
chains.

24. • A cyclic (ring) hydrocarbon is designated by
the prefix cyclo- which appears directly in
front of the base name.
• In summary, the name of the compound is
written out with the substituents in
alphabetical order followed by the base name
(derived from the number of carbons in the
parent chain). Commas are used between
numbers and dashes are used between letters
and numbers. There are no spaces in the
name.
• Here are some examples:

26. • Alkyl halides
The halogen is treated as a substituent on
an alkane chain. The halo- substituent is
considered of equal rank with an alkyl
substituent in the numbering of the parent
chain. The halogens are represented as
follows:
F fluoro-
Cl chloro-
Br bromo-
I iodo-

27. Here are some examples:
Alkenes and Alkynes - unsaturated hydrocarbons
Double bonds in hydrocarbons are indicated by replacing the
suffix -ene with -yne. If there is more than one double bond,
the suffix is expanded to include a prefix that indicates the
number of double bonds present (-adiene, -atriene, etc.).
Triple bonds are named in a similar way using the suffix -yne.
The position of the multiple bond(s) within the parent chain
is(are) indicated by placing the number(s) of the first carbon of
the multiple bond(s) directly in front of the base name.

28. Here is an important list of rules to follow:
• The parent chain is numbered so that the multiple bonds have
the lowest numbers (double and triple bonds have priority
over alkyl and halo substituents).
• When both double and triple bonds are present, numbers as
low as possible are given to double and triple bonds even
though this may at times give "-yne" a lower number than "-
ene". When there is a choice in numbering, the double bonds
are given the lowest numbers.
• When both double and triple bonds are present, the -en suffix
follows the parent chain directly and the -yne suffix follows
the -en suffix (notice that the e is left off, -en instead of -ene).
The location of the double bond(s) is(are) indicated before the
parent name as before, and the location of the triple bond(s)
is(are) indicated between the -en and -yne suffixes. See below
for examples.

29. • For a branched unsaturated acyclic hydrocarbon, the
parent chain is the longest carbon chain that contains
the maximum number of double and triple bonds. If
there are two or more chains competing for selection
as the parent chain (chain with the most multiple
bonds), the choice goes to
(1) the chain with the greatest number of carbon atoms,
(2) the # of carbon atoms being equal, the chain
containing the maximum number of double bonds.
• If there is a choice in numbering not previously
covered, the parent chain is numbered to give the
substituents the lowest number at the first point of
difference.
• Here are some examples:

31. • Alcohols
Alcohols are named by replacing the suffix -
ane with -anol.
• If there is more than one hydroxyl group (-
OH), the suffix is expanded to include a prefix
that indicates the number of hydroxyl groups
present (-anediol, -anetriol, etc.).
• The position of the hydroxyl group(s) on the
parent chain is(are) indicated by placing the
number(s) corresponding to the location(s) on
the parent chain directly in front of the base
name (same as alkenes).

32. • Here is an important list of rules to follow:
• The hydroxyl group takes precedence over alkyl groups and
halogen substituents, as well as double bonds, in the
numbering of the parent chain.
• When both double bonds and hydroxyl groups are present,
the -en suffix follows the parent chain directly and the -ol
suffix follows the -en suffix (notice that the e is left off, -en
instead of -ene).
• The location of the double bond(s) is(are) indicated before
the parent name as before, and the location of the hydroxyl
group(s) is(are) indicated between the -en and -ol suffixes.
See below for examples. Again, the hydroxyl gets priority in
the numbering of the parent chain.
• If there is a choice in numbering not previously covered,
the parent chain is numbered to give the substituents
the lowest number at the first point of difference.
Here are some examples

34. Aldehydes
 Aldehydes are named by replacing the suffix -
ane with -anal.
 If there is more than one -CHO group, the suffix
is expanded to include a prefix that indicates the
number of -CHO groups present (-anedial - there
should not be more than 2 of these groups on the
parent chain as they must occur at the ends).
 It is not necessary to indicate the position of the
-CHO group because this group will be at the end
of the parent chain and its carbon is
automatically assigned as C-1.

35.  Here is an important list of rules to follow:
• The carbonyl group takes precedence over alkyl groups and halogen
substituents, as well as double bonds, in the numbering of the parent
chain.
• When both double bonds and carbonyl groups are present, the -en
suffix follows the parent chain directly and the -al suffix follows the -en
suffix (notice that the e is left off, -en instead of -ene). The location of
the double bond(s) is(are) indicated before the parent name as before,
and the -al suffix follows the -en suffix directly. Remember it is not
necessary to specify the location of the carbonyl group because it will
automatically be carbon #1. See below for examples. Again, the
carbonyl gets priority in the numbering of the parent chain.
• There are a couple of common names which are acceptable as IUPAC
names. They are shown in the examples at the end of this list but at
this point these names will not be accepted by the computer.
Eventually they will be accepted.
• If there is a choice in numbering not previously covered, the parent
chain is numbered to give the substituents the lowest number at
the first point of difference.

36. • Here are some examples:

37. Ketones
Ketones are named by replacing the suffix -
ane with -anone.
• If there is more than one carbonyl group (C=O),
the suffix is expanded to include a prefix that
indicates the number of carbonyl groups present
(-anedione, -anetrione, etc.).
• The position of the carbonyl group(s) on the
parent chain is(are) indicated by placing the
number(s) corresponding to the location(s) on
the parent chain directly in front of the base
name (same as alkenes).

38. Here is an important list of rules to follow:
• The carbonyl group takes precedence over alkyl groups and
halogen substituents, as well as double bonds, in the
numbering of the parent chain.
• When both double bonds and carbonyl groups are present,
the -en suffix follows the parent chain directly and the -one
suffix follows the -en suffix (notice that the e is left off, -
en instead of -ene).
• The location of the double bond(s) is(are) indicated before
the parent name as before, and the location of the carbonyl
group(s) is(are) indicated between the -en and -one
suffixes. See below for examples. Again, the carbonyl gets
priority in the numbering of the parent chain.
• If there is a choice in numbering not previously covered,
the parent chain is numbered to give the substituents
the lowest number at the first point of difference.

39. • Here are some examples

40. Carboxylic Acids
• Carboxylic acids are named by counting the number of
carbons in the longest continuous chain including the
carboxyl group and by replacing the suffix -ane of the
corresponding alkane with -anoic acid.
• If there are two -COOH groups, the suffix is expanded
to include a prefix that indicates the number of -COOH
groups present (-anedioic acid - there should not be
more than 2 of these groups on the parent chain as
they must occur at the ends).
• It is not necessary to indicate the position of the -
COOH group because this group will be at the end of
the parent chain and its carbon is automatically
assigned as C-1.

41. Here is an important list of rules to follow:
• The carboxyl group takes precedence over alkyl groups and halogen
substituents, as well as double bonds, in the numbering of the parent
chain.
• If the carboxyl group is attached to a ring the parent ring is named and
the suffix -carboxylic acid is added.
• When both double bonds and carboxyl groups are present, the -en
suffix follows the parent chain directly and the -oic acid suffix follows
the -en suffix (notice that the e is left off, -en instead of -ene). The
location of the double bond(s) is(are) indicated before the parent
name as before, and the -oic acid suffix follows the -en suffix directly.
Remember it is not necessary to specify the location of the carboxyl
group because it will automatically be carbon #1. See below for
examples. Again, the carboxyl gets priority in the numbering of the
parent chain.
• There are several common names which are acceptable as IUPAC
names. They are shown in the examples at the end of this list but at
this point these names will not be accepted by the computer.
Eventually they will be accepted.
• If there is a choice in numbering not previously covered, the parent
chain is numbered to give the substituents the lowest number at
the first point of difference.

42. Here are some examples

43. Esters
• Systematic names of esters are based on the
name of the corresponding carboxylic acid.
Remember esters look like this:
• The alkyl group is named like a substituent using
the -yl ending. This is followed by a space. The
acyl portion of the name (what is left over) is
named by replacing the -ic acid suffix of the
corresponding carboxylic acid with -ate.

44. • Here are some examples

45. • Ethers
You are only expected to know how to name
ethers by their common names. The two alkyl
groups attached to the oxygen are put in
alphabetical order with spaces between the
names and they are followed by the word
ether. The prefix di- is used if both alkyl groups
are the same.
• Here are some examples:

46. IUPAC name of ether
• IUPAC’s nomenclature of ethers follows
different guidelines. According to IUPAC
naming, a substituent group containing more
carbon atoms is chosen as
parent hydrocarbon. The other substituent
group attached to the oxygen atom is named
with a prefix “oxy”. For example, CH3OC2H5 is
named as 1-methoxy ethane.

48. • Amines
You are only expected to know how to name
amines by their common names . They are
named like ethers, the alkyl (R) groups attached
to the nitrogen are put in alphabetical order with
no spaces between the names and these are
followed by the word amine.
• The prefixes di- and tri- are used if two or three
of the alkyl groups are the same.
NOTE: Some books put spaces between the parts
of the name, but we will not. Follow the
examples.

49. • Here are some examples:
IUPAC :-dimethylamino 1-methylaminoethane

50. • The IUPAC names are listed first and colored
blue. This system names amine functions as
substituents on the largest alkyl group. The
simple -NH substituent found in 1º-amines is
called an amino group. For 2º and 3º-amines a
compound prefix (e.g. dimethylamino)
includes the names of all but the root alkyl
group.

51. Functional group Prefix Suffix
carboxylic acids none -oic acid
aldehydes none -al
ketones none -one
alchols hydroxy- -ol
amines amino- -amine
ethers alkoxy- -ether
fluorine fluoro- none
chlorine chloro- none
bromine bromo- none
iodine iodo- non
Summary of functional groups

52. Isomerism in organic compounds
The word isomerism come from greek word
isomers (isos= equal, merso =share).
• Isomerism in organic chemistry is a phenomenon
shown by two or more organic compounds
having the same molecular formula but different
properties due to difference in arrangement of
atoms along the carbon skeleton (structural
isomerism) or in space (Stereo isomerism). The
chart summarizes the types of isomerism, and we
will discuss only structural isomerism in greater
detail.

53. Figure 1. Isomerism

54. Structural Isomerism
CHAIN ISOMERISM
It occurs when carbon atoms are linked to the
main chain in different ways. For example
Figure2. Pentane chain isomers

55. Position Isomerism
• It occurs when functional groups are attached
on different positions on a carbon chain. For
example
Figure 3. Position isomerism

56. Functional Isomerism
• It is a very interesting form of isomerism
where the compounds are different due to
different arrangements of atoms leading to
different functional groups. As functional
groups are usually the reactive center of a
molecule this leads to entirely different
properties. For example:
Figure 4. Functional isomerism

57. Metamerism
• This form of isomerism is rare and is limited to
molecules having a divalent atom like O or S
and alkyl groups around it. The main examples
come from ethers and thioethers
Figure 5. Metamerism

58. Tautomerism
• This isomerism is due to spontaneous intreconversion
of two isomeric forms with different functional groups.
The prerequisites for this is the presence of the C=O,
C==N or N=O in the usual cases and an alpha H atom.
The most usual is the (keto-enol) tautomerism, but
there can be others like nitro-acid and amine-imine
forms.
• In general the Keto form is more stable. Enols can be
forms by acid or base catalysis from the ketone and are
extensively used in making C-C single bonds in organic
synthesis.

59. Ring-Chain isomerism
• Here one isomer is an open chain molecule
and the other a cyclic molecule
Figure 7. Ring-chain isomerism
Propene is an alkene and cyclopropane an alkane, two
different classes of compounds

60. Thank you