Chapter Ten

1

• Practice

Vs
Vs
2
12.6 Naming Alkanes

• The current naming system (a.k.a. nomenclature)
  for organic compounds is the IUPAC (International
  Union of Pure and Applied Chemistry) system. In
  this system, a name consists of three parts

3
The parent part of the name is a name indicating
the number of carbons. For historical reasons
names indicating 1 through 4 carbons are common
names (i.e. they do not have a systematic base)
for 5 carbons and up, the name is derived from
the Greek word corresponding to the number.
4
The suffix part of the name is an ending that
tells what type of compound (alkane, alcohol,
etc.) the molecule belongs to.
For alkanes this suffix is -ane
5
CH4 Methane CH3CH3 Ethane CH3CH2CH3
Propane CH3CH2CH2CH3 Butane CH3CH2CH2CH2C
H3 Pentane CH3CH2CH2CH2CH2CH3
Hexane CH3CH2CH2CH2CH2CH2CH3
Heptane CH3CH2CH2CH2CH2CH2CH2CH3
Octane CH3CH2CH2CH2CH2CH2CH2CH2CH3
Nonane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 Decane
6

• We consider as substituents those groups of atoms
  attached to the main carbon-carbon chain of the
  molecule

7

• We can think of a substituent as being
  originated from an alkane by removing one of the
  hydrogens

This becomes the place of attachment to the main
carbon-carbon chain.

• Notice that all 4 Hs are equivalent so it does
  not matter in this case which one we take out.

8

• For most cases, the name of a substituent is
  derived from the name of the alkane with the same
  number of carbons by changing the ane ending by
  yl

Methane
Methyl
9

• Notice that in this case as well all the Hs are
  also equivalent so it does not matter which one
  we take out.

10

• The situation starts to get more complicated when
  the parent alkane has 3 or more carbons

• Hs and Hs are not equivalent!

11
Propane
Propyl
Isopropyl
12

• In condensed notation the name and formula of
  substituents are as follows

n-Butyl
Methyl
Ethyl
sec-Butyl or s-Butyl
n-Propyl
Isoproyl
Isobutyl
tert-Butyl or t-Butyl
13

• Primary carbon atom A carbon atom with one other
  carbon attached to it.
• Secondary carbon atom A carbon atom with two
  other carbons attached to it.
• Tertiary carbon atom A carbon atom with three
  other carbons attached to it.
• Quaternary carbon atom A carbon atom with four
  other carbons attached to it.

14

• Now that we know how to name the main chain
  (parentsuffix) and the substituents lets name
  complete alkanes

15
1) Determine the longest carbon chain.
10C
7C
8C
16

• 2) Number the chain according to the following
  rules
• Start by the end closest to a branch
• Start by the end that will give substituents the
  lower sequence of numbers.

CORRECT
INCORRECT
17
The main carbon-carbon chain contains 10 carbons.
Therefore the parent partsuffix part is Decane
18
3) Identify the substituents and number each
according to its point of attachment
Methyl on C3 Ethyl on C6 Methyl on C7
19
4) Write the name Use one Prefix entry for
each substituent type.
Methyl on C3 Ethyl on C6 Methyl on C7
We will have one prefix entry for methyl
and another for ethyl
20
Each Prefix entry has the form N-SubsType N ?
One or more numbers indicating the position(s) of
the substituent(s). There must be one number for
each substituent. If more than one number, they
should be separated by commas. SubsType ? Name of
the substituent (methyl, ethyl, etc.). If there
is more than one occurrence of a particular
substituent, its name should be preceded by di,
tri, tetra, penta, etc. (2,3,4,5). Finally,
prefixes should be ordered alphabetically.
21
Methyl on C3 Ethyl on C6 Methyl on C7
This becomes 3,7-dimethyl
This becomes 6-ethyl
6-ethyl-3,7-dimethyl-decane