Chap-3A - Chapter 3 Structure and Stereochemistry of...

Chapter 3
Structure and Stereochemistry
of Alkanes

Chapter 3
2
3-2 Molecular Formulas of Alkanes
•
All C-C single bonds
•
Saturated with hydrogens
• Ratio:
C
n
H
2n+2
•
Alkane homologs: CH
3
(CH
2
)
n
CH
3
•
Same ratio for branched alkanes
C
H
H
C H H
C H H
C H
H
H
H
Butane, C
4
H
10
C
H
H
C
C H
H
H
C
H
H
H
H
H
Isobutane, C
4
H
10

Chapter 3
3
3-3A Common Names
•
Isobutane, “isomer of butane”
•
Isopentane, isohexane, etc., methyl branch on next-to-last carbon in chain.
•
Neopentane, most highly branched
•
Five possible isomers of hexane, 18 isomers of octane and 75 for decane!
3-3 Nomenclature of Alkanes

Chapter 3
4
Pentanes
C
H
H
C H H
C H H
C H
C
H
H
H H
H
n
-pentane, C
5
H
12
C
H
H
C
C H
H
C
H
H
H
H
H
C H
H
H
isopentane, C
5
H
12
C CH
3
CH
3
H
3
C
CH
3
neopentane, C
5
H
12

Chapter 3
5
Longest Chain
•
The number of carbons in the longest chain determines the base name: ethane, hexane. (Listed in Table 3.2, page 81.)
•
If there are two possible chains with the same number of carbons, use the chain with the most substituents.
C CH
3
CH
2
CH
3
CH
CH
2
CH
2
CH
3
CH
CH
2
CH
3
H
3
C
H
3
C
3-3B IUPAC Names
The systematic way to name all organic compounds.

Chapter 3
6
Number the Carbons
•
Start at the end closest to the first attached group.
•
If two substituents are equidistant, look for the next closest group.
1
2
3
4
5
6
7
CH
H
3
C
CH
3
CH CH
2
CH
3
CH
2
CH
2
CH CH
3
CH
3

Chapter 3
7
Name Alkyl (Substituent) Groups
• CH
3
-, methyl
• CH
3
CH
2
-, ethyl
• CH
3
CH
2
CH
2
-,
n
-propyl
• CH
3
CH
2
CH
2
CH
2
-,
n
-butyl
CH
3
CH
CH
2
CH
3
sec-
butyl
CH
3
CH CH
3
CH
2
isobutyl
CH
3
CH
CH
3
isopropyl
C
H
3
C
CH
3
CH
3
tert
-butyl

Chapter 3
8
Propyl Groups
C H
H
H
C H H
C H H
H
n
-propyl
C H
H
H
C H
C H
H
H
isopropyl
H
A primary carbon
A secondary carbon

Chapter 3
9
Butyl Groups
C H
H
H
C H
C H H
C H
H
H
C H
H
H
C H
C H H
H
C H H
n
-butyl
sec
-butyl
H
H
A primary carbon
A secondary carbon

Chapter 3
10
Isobutyl Groups
C
H
H H
C C
H
H
C
H
H
H
H
C
H
H H
C C
H
H
C
H
H
H H
H
H
A primary carbon
A tertiary carbon
isobutyl
tert
-butyl

Chapter 3
11
Alphabetize
•
Alphabetize substituents by name.
•
Ignore di-, tri-, etc. for alphabetizing.
CH
H
3
C
CH
3
CH CH
2
CH
3
CH
2
CH
2
CH CH
3
CH
3
3-ethyl-2,6-dimethylheptane
•Prefixes used for the same type of (>2) alkyl groups
Di
= 2, Tri = 3, Tetra = 4, Penta
= 5

Chapter 3
12
Complex Substituents
•
If the branch has a branch, number the carbons from the point of attachment.
•
Name the branch off the branch using a locator number.
•
Parentheses are used around the complex branch name.
1
2 3
1-methyl-3-(1,2-dimethylpropyl)cyclohexane

Chapter 3
13
IUPAC Names: Summary
(1) Find the longest continuous chain of carbon
atoms. This is the
base name of the compound.
(2) Number the longest chain beginning with the end nearest a
substituent.