LEXTER C. SUPNET Dr. NATIVIDAD LORENZO
MAED-Physics 1st Semester, S.Y. 2014-2015
NOMENCLATURE OF ORGANIC COMPOUNDS
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.
A. ISOMERS-compounds that have the same molecular formula but differs in structural formula.
1. Skeletal isomers
2. Positional isomers
3. Functional isomers
5. Geometric Isomers
1. Skeletal Isomers- are constitutional isomers that have the same functional groups but differ
from each other in the connectivity of the carbon skeleton.
e.g. Butyl alcohol (1) and isobutyl alcohol (2) are constitutional isomers containing the same
functional groups, namely the alcohol group.
They differ from each other in the connectivity of the carbon skeleton.
Thus, 1 and 2 are skeletal isomers.
2. Positional Isomers
A variety of atoms or groups of atoms can be substituents on carbon chains, for example, Br. The
three monobromopentanes 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.
EXAMPLE 1: Identifying Isomers
Problem: Write structural formulas for all the possible isomers with the molecular formula C5H12.
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.
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.
Again, we complete the structure of this isomer by adding H atoms.
3. Finally, let’s consider a three-carbon chain with one-carbon branches. Again, there is only one
The number of isomers with the formula C5H12 is three.
PRACTICE 1 : Write the condensed structural formula for the five possible isomers with the formula
RULES IN NAMING ORGANIC COMPOUNDS
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 from ane 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
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. Keep in mind that in alphabetical order, we do not
consider the prefixes (di, tri…or symbols such as s and t).
Note: Do not try to memorize these rules at the outset. Refer to them as you proceed through the
examples, and they will become part of your vocabulary in organic chemistry.
SOME COMMON ALKYL GROUPS
Page5 Functional Groups – a specific region in an organic molecule that determines its chemical properties.
EXAMPLE 2: Naming an Alkane Hydrocarbon
Problem: Give an appropriate IUPAC name for the following compound, an important constituent of
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
PRACTICE 2: Give an appropriate IUPAC name for the following hydrocarbons:
EXAMPLE 3: Writing the Formula
Problem: Write a condensed structural formula for 4-t-butyl-2-methylheptane.
A. Because the compound is heptane, the longest chain of C atoms is seven.
B. Starting from the left, we attach a methyl group to the second C atom
C. Next, we attach a t-butyl group to the fourth C atom.
D. Finally we add the remaining hydrogen atoms to give each C atom four bonds.
PRACTICE 3: Write the condensed structural formula of the following:
a. 3-ethyl-2, 6-dimethylheptane
SOME CLASSES OF OR GANIC COMPOUNDS AND THEIR FUNCTIONAL GROUPS
Naming organic compounds is an important skill to acquire for anyone who is interested in being
informed in today’s issues. Many hot political issues today center around organic compounds and their
role as pesticides, pollutants, pharmaceuticals, preservatives, nutrients, manufacturing materials.
Everyone must be familiar of how organic compounds were named in order to recognize chemical
structures, properties, and reactions that are associated with the names of these chemical compounds.
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
Alkane R H CH3CH2CH2CH2CH2CH3 Hexane
Alkene CH2 CHCH2CH2CH3 1-Pentene
Alkyne CH3C CCH2CH2CH2CH2CH3 2-Octyne
Alcohol R OH CH3CH2CH2CH2CH2OH 1-Butanol
Alkyl halide R Xb CH3CH2CH2CH2CH2CH2CH2Br 1-Bromohexane
Ether R O R CH3 O CH2CH2CH3 1-Methoxypropane
(methyl propyl ether)c
Amine R NH2 CH3CH2CH2 NH2 1-Aminopropane
(ethyl propyl ketone)
aThe function group is shown in red, R stands for an alkyl group
bX stands for a halogen atom – F,CL,Br,I
dAr – stands for an aromatic (aryl) group such as the benzene ring