1. Chapter 10 Introduction to Organic Chemistry: Alkanes
10.2
Alkanes
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

2. Structural Formulas
Alkanes are written with structural formulas that are
expanded to show each bond.
condensed to show each carbon atom and its attached hydrogen atoms.
Expanded Condensed H
H C H CH4 , methane
In methane, CH4 the four valence electrons of carbon are shared with the single electrons of four hydrogen (H) atoms. Each pair of electrons is a single bond, which can be drawn as a line. When a structure is drawn to show each bond, it is called a complete structural formula.

3. Expanded and Condensed Structures

4. Structural Formulas
Condensed formulas are written for expanded structural formula by showing each carbon and the attached hydrogen atoms.
Expanded Condensed
H H H H
│ │ │ │
H─C ─C ─C ─C ─ H CH3─CH2─CH2─CH3

5. Names of Alkanes The names of alkanes
are determined by the IUPAC (International Union of Pure and Applied Chemistry) system.
end in –ane.
with 1-4 carbons in a chain use prefixes as follows.
Name # Carbons Structural Formula
Methane 1 CH4
Ethane 2 CH3CH3
Propane 3 CH3CH2CH3
Butane 4 CH3CH2CH2CH3

6. Names of Alkanes
Alkanes with 5-10 carbon atoms in a chain use Greek prefixes.
Name # Carbons Structural Formula
Pentane CH3CH2CH2CH2CH3
Hexane CH3CH2CH2CH2CH2CH3
Heptane CH3CH2CH2CH2CH2CH2CH3
Octane CH3CH2CH2CH2CH2CH2CH2CH3
Nonane CH3 CH2 CH2CH2CH2CH2CH2CH2CH3
Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

7. Learning Check A. Write the condensed formula for: H H H H H
H C C C C C H
H H H H H
B. What is its molecular formula?
C. What is its name?

8. Solution
A. CH3─CH2─CH2─CH2─CH3
B. C5H12
C. pentane

9. Writing Structural Formulas
Carbon atoms in a chain
maintain tetrahedral shape.
are connected in a zig-zag pattern.
are drawn as 2-dimensional.
Ccan be written in several conformations.

10. Some Structures for Butane

11. Hexane has Six Carbon Atoms
is an alkane with six carbon atoms in a continuous chain.
has a “zig-zag” look because each carbon atom is at the center of a tetrahedron.
is represented by a ball-and-stick model as shown below.

12. Learning Check Write the condensed structural formula for A. ethane.
B. heptane.

13. Solution Write the condensed structural formula for A. ethane CH3─CH3
B. heptane CH3─CH2─CH2─CH2─CH2─CH2─CH3

14. Cycloalkanes Cycloalkanes are cyclic alkanes.
have two hydrogen atoms fewer than the open chain.
are named by using the prefix cyclo- before the name of the alkane chain with the same number of carbon atoms.

15. Cycloalkanes The structural formulas of cycloalkanes are usually
represented by geometric figures,
Cyclopropane CH2
CH CH2
Cyclobutane CH CH2
CH CH2

16. More Cycloalkanes
Cyclopentane CH2
CH CH2
CH CH2
Cyclohexane
CH2

17. Learning Check Name the following. A. CH3─CH2─CH2─CH3 B.
C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3 D.

18. Solution Name the following: A. CH3─CH2─CH2─CH3 butane B. cyclopropane
C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3 octane D.
cyclohexane