Organic Chemistry I

Hydrocarbons:
•
Alkane and cycloalkane
: contains only C-C (single) bonds
•
Alkene and cycloalkene
: contains one or more C=C (double) bonds
•
Alkyne
: contains one or more C
≡
C (triple) bonds
•
Aromatic
: contains benzene ring and its derivative
Alkene, alkyne and aromatic rings are hydrocarbon functional groups because of the presence of multiple
bonds, even without heteroatoms.
Functional Groups involving heteroatoms
(see details in
Table 2.2, section 2.3
):
• Alkyl halides (haloalkanes), alcohol, ether, nitrile, nitro, amine, aldehyde, ketone, carboxylic acid, ester, amide,
anhydride
Chapter 2 Fundamental of Organic Structures | 43

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2.1 Structures of Alkenes
2.1.1 Structures and Different Structure Formulas
Alkane is the simplest hydrocarbon with only C-C single bonds. The chain alkane fits the general formula of
C
n
H
2n+2
(
n
: positive integer), and the number of H atoms reaches the maximum level in chain alkanes. The names and structures
of straight-chain alkanes up to ten carbons are listed in the table below.
Number of Carbons
Name
Formula (C
n
H
2n+2
)
Condensed Structure
1
methane
CH
4
CH
4
2
ethane
C
2
H
6
CH
3
CH
3
3
propane
C
3
H
8
CH
3
CH
2
CH
3
4
butane
C
4
H
10
CH
3
CH
2
CH
2
CH
3
5
pentane
C
5
H
12
CH
3
CH
2
CH
2
CH
2
CH
3
6
hexane
C
6
H
14
CH
3
CH
2
CH
2
CH
2
CH
2
CH
3
7
heptane
C
7
H
16
CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
CH
3
8
octane
C
8
H
18
CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
3
9
nonane
C
9
H
20
CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
3
10
decane
C
10
H
22
CH
3
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
3
Table 2.1 Names and Structures of Straight-Chain Alkanes
The primary sources of alkanes are natural gas and petroleum. Natural gas contains mainly methane (70 –90%) and
some ethane. Petroleum refining separates crude oil into different fractions and each fraction consists of alkanes of
similar number of carbons. Propane and butane are common fuels in propane gas burners and cigarette lighters. Alkanes
with 5 to 8 carbons are the major components of gasoline, while diesel contains alkanes ranging from 9 to 16 carbons.
As the number of carbons increase, the boiling point and viscosity of alkanes increase.
There are a variety of formats to show the structural formulas of organic compounds, it is important to be able to
recognize different formula drawings, and use them correctly to represent the structures.