Condensed Structural Formulas
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Condensed Structural Formulas

Although structural formulas have the tremendous value of showing which atoms are bonded to which other atoms, they do have a few drawbacks. One is that they are two-dimensional and the molecules they represent are three-dimensional. I have already mentioned that we need to use perspective drawings and models to get around this problem. Another drawback is that they take up a lot of space and a lot of time to write and they are terrible to type (though not as bad as electron dot diagrams).

One way of getting around this problem is the use of condensed structural formulas. In the condensed structural formula, each carbon atom is written separately and following each carbon atom are listed the other atoms that are bonded to that carbon atom. In this case the first carbon atom has three hydrogen atoms bonded to it, the second carbon atom has two hydrogen atoms bonded to it, the third carbon atom has two hydrogen atoms, and the fourth carbon atom has three hydrogen atoms. Another even more condensed way of writing a condensed structural formula is this. It points out that there are two CH2 groups in the middle of the molecule by having (CH2)2 in the middle of the formula.
Complete Structural Formula

H H H H
| | | |
H-C-C-C-C-H
| | | |
H H H H

Condensed Structural Formula

CH3CH2CH2CH3
or
CH3(CH2)2CH3

 

This structural formula for this compound can also be condensed. From left to right, this formula shows a carbon atom with three hydrogen atoms bonded to it, then another carbon atom with one hydrogen atom and also two more carbon atoms, each having three hydrogen atoms bonded to them. You can see that sometimes these condensed structural formulas get a bit tricky as far as figuring out what is bonded to what. However, you can do it if you remember that each carbon atom has four bonds. Another way of showing the condensed structural formula of this compound is to show a carbon atom bonded to one hydrogen atom and also to three other groups, each of which is a carbon atom bonded to three hydrogen atoms.
Complete Structural Formula

H   H   H
|   |   |
H - C - C - C - H
|   |   |
H H-C-H H
|
H

Condensed Structural Formula

CH3CHCH3CH3
or
CH(CH3)3

These examples are also shown in your workbook as example 6.

 

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E-mail instructor: Eden Francis

Clackamas Community College
2001, 2003 Clackamas Community College, Hal Bender