| The functional group for an alcohol is the hydroxyl group, -OH. With the
exception of carboxylic acids and carbohydrates (which we will deal with later), the
presence of an -OH group bonded to a carbon atom makes the molecule an alcohol. |
|
| You can see the -OH group in the structural formulas shown here (and in
the first three examples in your workbook). |
H
|
H-C-O-H
|
H |
H H
| |
H-C-C-OH
| |
H H |
H H H
| | |
H-C - C - C-H
| | |
H OH H |
|
| Although it is not apparent in the structural formulas, there is an angle
in these molecules where the oxygen atom is bonded to the carbon and hydrogen atoms. This
is very similar to the angle in a water molecule. Because of this angle and the high
electronegativity of oxygen, these molecules are polar--at least in the vicinity of the
-OH group. |
|
| These models show that angle. But to get a better feel for or sense of the
polarity of alcohol molecules, when you are in the lab you should look at the
space-filling model of an alcohol molecule that is on display there. Also look at the
ball-and-stick model. Compare the models to one another and to the structural formula of
the alcohol, all the while paying particular attention to the hydroxyl group. |
|
![Models of C-O-H and H-O-H.[63mod01.JPG]](images/63mod01.JPG)
![Models of ethanol.[63mod02.JPG]](images/63mod02.JPG)
