(ch3)2-ch-ch(ch3)-ch2-ch3
Answers
Answer:-37-
NAMING ORGANIC COMPOUNDS
1. ALKANES
(CnH2n + 2)
Formula
carbons (n) Name
Number of Number of
carbons (n) Name
Formula
(CnH2n + 2)
1
2
3
4
5
6
7
8
9
10
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
Table 1 Straight-chain alkane (n-alkane) names
The suffix -ane is added to the end of each name to show that the compound is an alkane. Thus,
butane is the four-carbon alkane, heptane is the seven-carbon alkane, and so on. The names of the first
ten alkanes, given in Table 1, should be memorized. Larger alkanes, such as icosane (C20H42), have
more complicated names and are outside the scope of this course.
If one hydrogen atom is removed from an alkane, the remaining part of the molecule is called an alkyl
group. Alkyl groups are named by replacing the -ane ending of the parent alkane by an -yl ending. For
example, removing a hydrogen atom from methane gives the methyl group. Similarly, removal of a
hydrogen from an end carbon of any n-alkane produces the series of straight-chain alkyl (n-alkyl)
groups show in Table 2.
Alkane Alkyl group
Table 2 Straight-chain alkyl (n-alkyl) groups
Alkane Alkyl group
CH4
CH3CH3
CH3CH2CH3
CH3CH2CH2CH3
Methane
Ethane
Propane
Butane
Methyl (Me)
Ethyl (Et)
Propyl(Pr)
Butyl (Bu)
(Abbreviations in parentheses)
CH3−
CH3CH2−
CH3CH2CH2− or n-C3H7
CH3CH2CH2CH2− or n-C4H9
Using the IUPAC (International Union of Pure and Applied Chemistry) rules, most branched-chain
alkanes can be named by the following four steps. For more complex alkanes, a fifth step is needed.
Step 1 Find the parent hydrocarbon
a) Find the longest continuous carbon chain present in the molecule and use the name of
that chain as the parent name. The longest chain may not always be obvious from how
the structure is written, as shown below.
-38-
CH3CH2CH2CH-CH3
CH2CH3
Named as a substituted hexane
CH3-CH
CH3CH2
CH-CH2CH3
CH2CH2CH3
Named as a substituted heptane
b) If two different chains of equal length are present, choose the one with the most
substituents as the parent:
CH3CH
CH3
CHCH2CH2CH3
CH2CH3
CH3CH
CH3
CHCH2CH2CH3
CH2CH3
Named as a hexane with two
substituents
NOT as a hexane with one
substituent
Step 2 Number the atoms in the main chain
a) Beginning at the end nearer the first branch, number each carbon atom in the longest
chain:
7 6
5 4
3 2 1
CH3-CH
CH3CH2
CH-CH2CH3
CH2CH2CH3
CH3-CH
CH3CH2
CH-CH2CH3
CH2CH2CH3
1 2
3 4
5 6 7
NOT
The first branch occurs at C3 in the proper numbering system but at C4 in the improper
system.
b) If there is branching an equal distance from both ends of the longest chain, number
from the end nearer the second branch:
9
8
CH3-CH
CH3CH2
CH2 CH2 CH
CH3
CHCH2CH3
CH2CH3
7 6 5
3 4
1 2
4 3 2 1
5 6 7
NOT
CH3-CH
CH3CH2
CH2 CH2 CH
CH3
CHCH2CH3
CH2CH3
8
9
-39-
Step 3 Identify and number the substituents
a) Using the numbering arrived at in step 2, assign a number to each substituent according
to its point of attachment to the main chain:
b) If there are two substituents on the same carbon, assign them both the same number.
There must always be as many numbers in the name as there are substituents:
Step 4 Write out the name as a single word, using hyphens to separate the different prefixes and
using commas to separate numbers. If two or more different substituents are present, cite
them in alphabetical order. If two or more identical substituents are present, use one of the
prefixes di-, tri-, tetra-, and so forth. Do not use these prefixes for deriving the alphabetical
order, however. Some examples are shown below.
5 6 7
3 4
1 2
CH3CH2CH2CH-CH3
CH2CH3
CH3-CH
CH3CH2
CH-CH2CH3
CH2CH2CH3
2 1
3
6 5 4
3-Methylhexane
4-Ethyl-3-methylheptane
CH3CH
CH3
CHCH2CH2CH3
CH2CH3
1 2 3
4 5 6
CH3CH2C
CH3
CH2
CH3CH2
CHCH3
CH3
3 2 1
4 6 5
3-Ethyl-2-methylhexane 4-Ethyl-2,4-dimethylhexane
9
7 6 5 4 3 2 1
CH3-CH
CH3CH2
CH2 CH2 CH
CH3
CHCH2CH3
CH2CH3
8
3-Ethyl-4,7-dimethylnonane
Complex substituents
Application of the preceeding four steps allows us to name many alkanes. However, in some very
complex cases a fifth step is needed. This occurs when a substituent is, itself, branched (i.e., has
sub-branching).