This document provides an overview of organic chemistry nomenclature. It begins by discussing the early history of organic chemistry and defining key terms. The main sections cover naming conventions for alkane hydrocarbons using IUPAC rules and identifying isomers based on skeletal structure and substituent position. Examples are provided to demonstrate naming organic compounds and writing structural formulas. Common functional groups such as alcohols, aldehydes, and aromatics are defined along with their IUPAC nomenclature.

1. NOMENCLATURE OF ORGANIC
COMPOUNDS
Prepared by:
MR. LEXTER C. SUPNET
MAED-Physics

2. REVIEW
FRIEDRICH WÖHLER (1828) – set out to synthesize ammonium cyanate, NH4OCN, as in the
reaction
Δ
AgOCN(s) + NH4Cl(aq) AgCl(s) + NH4OCN(aq)
The white crystalline solid he obtained from the solution had none of the properties
of ammonium cyanate, even though it had the same composition. The compound was not
NH4OCN but (NH2)2OCN – urea, an organic compound.
As Wöhler excitedly reported to J.J. Berzulius, “I must tell you that I can make urea
without the use of kidneys, either man or dog, Ammonium cyanate is urea.”

3. REVIEW
ORGANIC CHEMISTRY – the branch of chemistry concerned with the compounds of carbon:
originally confined to the compounds produced by living organism but now extended to
include man-made substances based on carbon, such as plastics.
(Collins English Dictionary – Complete & Unabridged 2012 Digital Edition)
Carbon is singled out for special study because of the ability of C atoms to form strong
covalent bonds with one another allows them to join together into straight chains, branched
chains, and rings.

4. REVIEW
Organic compounds – contain carbon and oxygen atoms or carbon and hydrogen in combination
with a few other types of atoms, such as oxygen, nitrogen, and sulfur.
Hydrocarbons– simplest organic compound which consists of Carbon and Hydrogen atoms.
Methane (Ch4) – the simplest organic compound.

5. ISOMERS
ISOMERS – compounds that have the same molecular formula but differs in structural formula.
TYPES:
1. SKELETAL ISOMERS
2. POSITIONAL ISOMERS
3. FUNCTIONAL ISOMERS
4. STEREOISOMERS
5. GEOMETRICAL ISOMERS

6. SKELETAL ISOMERS
Skeletal isomers are constitutional isomers that have the same functional groups but differ
from each other in the connectivity of the carbon skeleton.

7. EXAMPLE 1: IDENTIFYING ISOMERS
Write structural formulas for all the possible isomers with the molecular formula C5H12.
Solution:
1. Write the longest chain of C atoms from left to right. This gives the straight-chain formula labeled (1).
To finish this structure, we add an appropriate number of H atoms (12, in this case) to give each C
atom four bond.
H H H H H
H C C C C C H
H H H H H
(1)

8. EXAMPLE 1: IDENTIFYING ISOMERS
2. Now, look for isomers with four C atoms in the longest chain and one C atom as a branch (five C
atom in all). There is only one possibility.
C
C C C C
(2)
Again, we complete the structure of this isomer by adding H atoms.
H
H C H
H H H
H C C C C H
H H H H

9. EXAMPLE 1: IDENTIFYING ISOMERS
3. Finally, let’s consider a three-carbon chain with one-carbon branches. Again, there is only
one possibility.
C CH3
C C C that is, CH3 C CH3
C CH3
(3)
The number of isomers with the formula C5H12 is three.

10. ISOMERS OF C5H12
H H H H H
H C C C C C H
H H H H H
(1)
CH3
CH3 C CH3
CH3
(3)
H
H C H
H H H
H C C C C H
H H H H
(2)
(1) (2) (3)

11. PRACTICE
Write the condensed structural formula for the five possible isomers with the formula C6H16.
ANSWERS:
1. CH3CH2CH2CH2CH2CH2CH3
2. (CH3)2CHCH2CH2CH3
3. CH3CH2CH(CH3)CH2CH3
4. (CH3)2CHCH(CH3)2
5. (CH3)3CCH2CH3

12. POSITIONAL ISOMERISM
A variety of atoms or groups of atoms can be substituents on carbon chains, for
example, Br. The threemonobromopentanes possess the same carbon skeleton. Because they
differ in the position of the bromine atom of the carbon chain, these structural isomers are
also called positional isomers.
1-Bromopentane 2-Bromopentane 3-Bromopentane
CH3CH2CH2CH2CH2Br CH3CH2CH2CH2CHCH3
Br
CH3CH2CHCH2CH3
Br
Br Br
Br

13. NOMENCLATURE
Early organic chemists often assigned names related to the origin or properties of
new compounds. Some of these names are still in common use. Citric acid if found in citrus
fruit; uric acid is present in urine; formic acid is found in ants (from the Latin word for ant,
formica); and morphine induces sleep (from Morpheus, the ancient Greek god of sleep). As
thousands upon thousands of new compounds were synthesized, it became apparent that a
system of common names was unworkable. Following several interim systems, one
recommended by the International Union of Pure and Applied Chemistry (IUPAC)was adopted.

14. RULES IN NAMING ORGANIC COMP0UNDS
1. Select the longest continuous carbon chain in the molecule, and use the hydrocarbon name of
this chain as the base name. Except for the common names methane, ethane, propane, and
butane, standard Greek prefixes relate the name to the number of C atoms in the chain, as in
pentane (C5), hexane (C6), heptane (C7), octane (C8),…
2. Consider every branch of the main chain to be substituent derived from another hydrocarbon.
For each of these substituents, change the ending of its name fromane to yl. That is, the alkane
substituent becomes alkyl group.
3. Number the C atoms of the continuous base chain so that the substituents appear at the lowest
number possible.
4. Name each substituent according to its chemical identity and the numbers of the C atom to
which it is attached. For identical substituents use di, tri, tetra, and so on, and write the
appropriate carbon number for each substituent.
5. Separate the numbers from one another by commas, and from letters by hyphens.
6. List the substituents alphabetically by name.

15. SOME COMMON ALKYL GROUPS
NAME STRUCTURAL FORMULA
Methyl CH3
Ethyl CH2CH3
Propyla CH2CH2CH3
Isopropyl CH3CHCH3
Butyla CH2CH2CH2CH3
Isobutyl CH3
CH2CHCH3
s-butylb CH3CHCH2CH3
t-butylc CH3
CH3CCH3
aIn the past, the prefix normal or n- was used for a straight-chain
alkyl group, such as n-propyl or n-butyl
bs = secondary
Ct = tertiary

16. ORGANIC COMPOUNDS AND THEIR FUNCTIONAL
GROUPS
Functional Groups – a specific region in an organic molecule that determines its chemical
properties.

17. EXAMPLE: NAMING AN ALKANE HYDROCARBON
Give an appropriate IUPAC name for the following compound, an important constituent of
gasoline.
CH3 CH3
CH3 C CH2 CH CH3
1 2 3 4 5
CH3
Solution:
The C atoms are numbered in red, and the side-chain substituents to be named are shown in
blue. The longest chain of C atoms is five, and the carbons are numbered so that the one with
two substituent groups is number 2, instead of number 4. Each substituent is a methyl group, -
CH3. Two methyl groups are on the second C atom, and one methyl group is on the fourth C
atom. The correct name is
2,2,4-trimethylpentane

18. PRACTICE: NAMING AN ALKANE HYDROCARBON
Give an appropriate IUPAC name for the following hydrocarbons:
A. CH3CH2CH(CH3)CH2CH2C(CH3)2CH2CH2CH3
B. CH3CH2CH(CH3)CH2CH2CH(CH3)CH2CH3
ANSWER:
A. 3,3,6-trimethylnonane
B. 3,6-dimethyloctane

19. EXAMPLE: WRITING THE FORMULA
Write a condensed structural formula for 4-t-butyl-2-methylheptane.
SOLUTION:
A. Because the compound is heptane, the longest chain of C atoms is seven.
C C C C C C C
B. Starting from the left, we attach a methyl group to the second C atom.
CH3
C C C C C C C

20. C. Next, we attach a t-butyl group to the fourth C atom.
CH3
CH3 C CH3
CH3
C C C C C C C
D. Finally we add the remaining hydrogen atoms to give each C atom four bonds.
CH3
CH3 C CH3
CH3
CH3 CH CH2 CH CH2 CH2 CH3

21. PRACTICE
Write the condensed structural formula of the following:
• 3-ethyl-2, 6-dimethylheptane
• 3-isopropyl-2-methylpentane
Answer:
• CH3CH(CH3)CH(CH2CH3)CH2CH2CH(CH3)CH3
• CH3CH(CH3)CH[CH(CH3)2]CH2CH3

22. ALKANE
Class
General
Structural
Formula Example
Name of
Example
Alkane R H CH3CH2CH2CH2CH2CH3 Hexane
*The functional group is shown in red, R stands for an alkyl group
Exercise: Give the appropriate IUPAC name of the alkane
 CH3CH2CH2CH2CH3
Ans: Pentane

23. ALKENE
Class
General
Structural
Formula Example
Name of
Example
Alkene C C CH2 CHCH2CH2CH3 1-Pentene
*The functional group is shown in red, R stands for an alkyl group
Exercise: Give the appropriate IUPAC name of the alkene
 CH3CH CH2CH2CH2CH2CH3
 CH3CH2CH2C CH2
CH2CH3
Ans:
2-heptene
2ethy,1-pentene

24. ALKYNE
Class
General
Structural
Formula Example
Name of
Example
Alkyne C C CH3C CCH2CH2CH2CH2CH3 2-Octyne
*The functional group is shown in red, R stands for an alkyl group
Exercise: Give the appropriate IUPAC name of the Alkyne
 CH3CHC CCH3
CH3
Ans: 4-methy,2-pentyne

25. ALCOHOL
Class
General
Structural
Formula Example
Name of
Example
Alcohol R OH CH3CH2CH2CH2CH2OH 1-Butanol
*The functional group is shown in red, R stands for an alkyl group
Exercise: Give the appropriate IUPAC name of the alcohol
 CH3CH2OH
Ans: Methanol

26. ALKYL HALIDE
Class
General
Structural
Formula Example
Name of
Example
Alkyl halide R X** CH3CH2CH2CH2CH2CH2CH2Br 1-Bromohexane
*The functional group is shown in red, R stands for an alkyl group
**X stands for a halogen atom – F, Cl, Br, I
Exercise: Give the appropriate IUPAC name of the alkyl halide
 CH3CH(Cl)CH2CH3
Ans: 2-chlorobutane

27. ETHER
Class
General
Structural
Formula Example
Name of
Example
Ether R O R CH3 O CH2CH2CH3 1-Methoxypropane
(methyl propyl ether)
*The functional group is shown in red, R stands for an alkyl group
**X stands for a halogen atom – F, Cl, Br, I
Exercise: Give the appropriate IUPAC name of the ether
 CH3CH2OCH2CH3
Ans: diethyl ether

28. AMINE
Class
General
Structural
Formula Example
Name of
Example
Amine R NH2 CH3CH2CH2 NH2 1-Aminopropane
(propylamine)
*The functional group is shown in red, R stands for an alkyl group
**X stands for a halogen atom – F, Cl, Br, I
Exercise: Give the appropriate IUPAC name of the amine
 CH3CH(NH2)CH2CH2CH3
Ans: 2-Aminopentane

29. ALDEHYDE
Class
General
Structural
Formula Example
Name of
Example
Aldehyde O
R C H
O
CH3CH2CH2C H
Butanal
(butyraldehyde)
*The functional group is shown in red, R stands for an alkyl group
Exercise: Give the appropriate IUPAC name of the aldehyde
 H2C O
Ans: Methanal (formaldehyde)

30. KETONE
Class
General
Structural
Formula Example
Name of
Example
Ketone O
R C R
O
CH3CH2CH2CCH2CH3
3-Hexanone
(ethyl propyl ketone)
*The functional group is shown in red, R stands for an alkyl group
Exercise: Give the appropriate IUPAC name of the ketone
O
 CH3CCH3
Ans: Propanone (Acetone)

31. CARBOXYLIC ACID
Class
General
Structural
Formula Example
Name of
Example
Carboxylic
acid
O
R C OH
O
CH3CH2CH2C OH
Butanoic acid
(butyric acid)
*The functional group is shown in red, R stands for an alkyl group
Exercise: Give the appropriate IUPAC name of the Carboxylic acid
O
 HC OH
Ans: Methanoic acid (formic acid)

32. ESTER
Class
General
Structural
Formula Example
Name of
Example
Ester O
R C OR
O
CH3CH2CH2C OCH3
Methyl butanoate
(methyl butyrate)
*The functional group is shown in red, R stands for an alkyl group
Exercise: Give the appropriate IUPAC name of the ester
O
 HOC OCH3
Ans: Methyl methanoate

33. AMIDE
Class
General
Structural
Formula Example
Name of
Example
Amide O
R C NH2
O
CH3CH2CH2C NH2
Butanamide
(butyramide)
*The functional group is shown in red, R stands for an alkyl group
Exercise: Give the appropriate IUPAC name of the amide
O
 CH3CH2C NH2
Ans: Propanamide

34. ARENE
Class
General
Structural
Formula Example
Name of
Example
Arene Ar H**
CH2CH3
Ethylbenzene
*The functional group is shown in red, R stands for an alkyl group
**Ar stands for aromatic (aryl) group such as the benzene ring
Exercise: Give the appropriate IUPAC name of the arene
 CH3CH2 CH3
Ans: 1-ethyl,4-methylbenzene

35. ARYL HALIDE
Class
General
Structural
Formula Example
Name of
Example
Aryl halide Ar X**
Br
Bromobenzene
*The functional group is shown in red, R stands for an alkyl group
**Ar stands for aromatic (aryl) group such as the benzene ring
***X stands for halogen atom – F, Cl, Br, I

36. PHENOL
Class
General
Structural
Formula Example
Name of
Example
Phenol Ar OH**
Cl OH
4-Chlorophenol
*The functional group is shown in red, R stands for an alkyl group
**Ar stands for aromatic (aryl) group such as the benzene ring
***X stands for halogen atom – F, Cl, Br, I
Exercise: Give the appropriate IUPAC name of the phenol
CH3
OH
Ans: 2-methylphenol

37. THANK YOU!

38. REFERENCES
• PETRUCCI, R.H., HARDWOOD, W.S., HERRING, F.G. 2002. General Chemistry: Principles and
Modern Applications. 8th Edition. Pearson Education South Asia Pte. Ltd. Singapore.
• Collins English Dictionary – Complete & Unabridged 2012 Digital Edition
• http://science.uvu.edu/ochem/index.php