ChemQuest 86
Name: ____________________________
Date: _______________
Hour: _____
Information: The Simplest Organic Compounds
Organic chemistry is incredibly diverse and includes the study of millions of compounds. The
element carbon is the distinguishing mark of all organic compounds. Carbon is special in that it
can bond with itself to form long molecular chains. The most basic organic compounds contain
only carbon and hydrogen. When the carbon chains are composed of only single bonds, the
compounds are called “alkanes.”
Below, are the four simplest alkanes:
methane
ethane
propane
butane
Critical Thinking Questions
1. Hydrogen will never be involved in a double bond like this:
. Offer an explanation.
Hydrogen is “content” with only two electrons since the 1st energy level only holds
two.
2. A pentagon is a shape with ______
sides. How many carbon atoms does the alkane,
5
how many?
pentane, have?
3. Based on your answer to question 2, draw the molecule pentane.
4. Draw the molecule hexane.
5. Heptane has 7 sides. Draw it and octane below.
Heptane:
Octane:
Information: Another Way to Write Structures
All of the alkanes you have drawn have shown each of the bonds explicitly. Since all of the
bonds are similar, we can assume what they look like without needing to draw every bond. Here
are a few examples:
CH3—CH2—CH3
CH3
propane
CH3—CH2—CH2—CH3
CH3—CH2—CH2—CH2—
butane
pentane
Critical Thinking Questions
6. Using the above notation draw hexane.
CH3—CH2—CH2—CH2—CH2—CH3
7. Draw nonane (9 carbons) and decane (10 carbons).
CH3—CH2— CH2—CH2—CH2—CH2—CH2—CH2—CH3
CH3—CH2— CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH3
Information: Branches
All of the alkanes we have looked at so far have been “straight chains.” It is very, very common
for organic molecules to have branches. Here are a few examples.



CH3
|
CH3—CH2—CH2—CH2—CH3
CH3
|
CH3—CH2—CH3



This molecule is called “3-methylpentane”.
Notice that the branch is called “methyl.”
Also notice that the branch is attached to the
3rd carbon atom in a chain of 5 carbons.
This molecule is called “2-methylpropane”
Notice that the branch is called “methyl.”
Also notice that the branch is on the 2nd
carbon atom in the chain of 3 carbon atoms.



This molecule is called “4-ethyloctane”
Notice that the branch is called “ethyl.”
Also notice that the branch is on the 4th
carbon atom in the chain of 8.
CH2—CH3
|
CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH3
Critical Thinking Questions
8. As you saw above, a branch with one carbon is called “methyl.” A branch with two
carbon atoms is called “ethyl.” Try to write the name for a branch with three carbon
atoms.
propyl
9. In the above information section you saw the structure for 2-methylpropane. Expanding
the structure to show all of the bonds looks like this:
Now, you draw the expanded structure for 3-methylpentane:
10. Study the following molecule:
CH2—CH3
|
CH3—CH2—CH2—CH2—CH2—CH2—CH3
a) The chain is a heptane chain. Why?
It has 7 carbon atoms.
b) The branch is called “ethyl.” Why?
The branch has 2 carbon atoms.
c) Which carbon is the branch attached to—the 1st, 2nd, or 3rd?
d) Name the compound.
3-ethylheptane
3rd
11. Draw the molecule for 3-methylhexane.