From
A guide to naming organic compounds. This is Section 4:
Functional Groups
Organic compounds are not simply hydrocarbons. Organic compounds can also include elements other than
just hydrogen and carbon. Compounds such as alcohols, aldehydes, carboxylic acids or ketones contain funcitonal
groups and can be named using the IUPAC naming system.
What is a functional group?
A functional group is a part of an organic molecule. The functional group plays a large role in
determining the properties of the compound hence the name 'functional group'. Generally
functional groups dicate how the molecule reacts with different chemicals too. Seeing as
I have really only done basic organic chemistry I can only cover a few functional groups. Below are ASCII representations of
functional groups that I know:
Haloalkane: Ketone:
R-X R-C=O
|
R'
Alcohol:R-O-H Aldehyde:
R-C=O
|
H
Carboxylic Acid:
Ester: R-C=O
R-C=O |
| O
O-R' |
H
Amide:
R-C=O
|
R'-N-R"
VSEPR theory states that the actual shapes of these molecules
will not be exactly what's drawn above, but that's not important for our purposes.
What the hell are these Rs and R's? The Rs represent either an alkyl group or a hydrogen. It's easier for me to put an R there rather than a hydrocarbon. An R' represents another hydrocarbon or hydrogen that is not nessicarily the same as the R. These are just used for simplicity's sake.
So I suppose I'll start from the top:
Haloalkanes
As drawn above, haloalkanes take the form of
R-X
where R is the rest of the molecule. The X represents
a
halide. A halide is one of the elements down the coloumn next to the
noble gases (
Fluorine,
Chlorine,
Bromine or
Iodine. I have never seen astatine in an organic molecule and therefore I will ignore it in this writeup).
So the following are haloalkanes:
H H H H H
| | | | |
H-C-Cl H-C-C-C=C-C-I
| | | | |
H H F I Br
Br I F
\ / |
C=C F-C-F
/ \ |
I Br F
Haloalkanes are simply hydrocarbons that have at least one halide attached to the carbon chain in place of a hydrogen. Haloalkanes are relativly simple to name. All you have to do is find the position of the haloalkanes on the chain in the same way that you do
for double and triple bonds except now, rather than number from the end that will result in the smallest numbers for the branches that come off the chain, we number from the end that will give the halide branches the lowest number. For example the following compound is named 1-iodo-4-methylhexane, not 6-iodo-3-methylhexane.
H H H H H H
| | | | | |
H - 6 - 5 - 4 - 3 - 2 - 1 - H
| | | | | |
H H H-C-H H H I
|
H
The prefixes that are added to the base chain are:
Halide Prefix
______________________________
Iodine iodo-
Chlorine chloro-
Fluorine fluoro-
Bromine bromo-
You use these prefixes in much the same way you used the prefixes for branches in
Structural Isomerism
Here are some molecules as examples:
1,2-diflouri-3-iodoprop-1-ene
Trichloromethane H F F
Cl | | |
| I-C-C=C-H
Cl-C-Cl | |
| H H
H
H H H H
| | | | <-- 1-Bromobutane
Br-C-C-C-C-H
| | | |
H H H H
Alcohols
An alcohol functional group is represented by a '-O-H' in a molecule. Alcohols are a little harder to name than haloalkanes. When an alcohol group is on the end of a molecule you can simply drop the 'e' and add an -ol suffix to the end of the chain's name:
H H H H H
| | | | <--Butanol | <--Methanol
H-C-C-C-C-O-H H-C-H
| | | | |
H H H H O-H
However, that suffix does not suffice with a molecule such as the one below:
H H H
| | |
H-C-C-C-O-H
| | |
O H H
|
H
For this case we need to use the prefix 'hydroxy-'. The name of the molecule is, therefore, 1,3-hydroxy-propane. There are a number of ways to name this molecule, but I don't plan on listing all the
permutations. One popular alternative, however, is this: propane-1,3-diol. This is the way that I prefer to name alcohols. I am told that both ways can be used. The suffix -diol and -triol can be used to signify a molecule with 2 and 3 alcohol groups respectivly.
Now for some alcohol examples:
H H H H H
| | | | | <-- 3-hydroxymethyl-pentane
H - C - C - C - C - C - H
| | | | | H
H H H-C-H H H |
| H-C-O-H
O |
| H <-- Methanol
H
O-H H-O
| tetrahydroxymethane--> |
H-C-O-H H-O-C-O-H
| <-- Methanetriol |
O-H O
|
H
Aldehydes
Aldehydes are represented by this:
R-C=O
|
H
Aldehydes are given the suffix -al in much the same way that alcohols are given the suffic -ol. If there are more than one aldehyde groups on the same chain then you use 'dial' or whatever to signify the case.
Some examples:
H H H H
| | | <--Butanal |
H-C-C-C-C=O O=C-C=O
| | | | |<--Ethanedial
H H H H H
Carboxylic Acids
Carboxylic Acids are a functional group represented by this:
-R-C=O
|
O-H
These molecules are also easy to name. Just put an '-oic acid' in as a suffix.
Examples:
H H H
| | |
H-C-C-C-C=O H
| | | |<--Butanoic Acid | <-- Ethanoic Acid
H H H O H-C-C=O
| | |
H H O-H
Amides
As with Aldehydes and Carboxylic Acids, to name an amide you simply use a suffix. With amides, the suffix is '-amide'. Amides are represented like this:
R-C=O
|
H-N-H
Example:
H H H H
| | | | <--Butanamide
H-C-C-C-C=O
| | | |
H H H N-H
|
H
Ketones and Esters
These two functional groups are so closely related that I thought that I should put them together. They are represented byt he following:
Ketone: Esters:
-R=O R'=O
| |
R' O-R
As you can see, Ketones and Esters join two carbon chains together. Because of this, a simple suffix will not suffice.
H H This molecule's R group is an ethly group.
| | Therefore the first part of this
H-C-C=O molecules name is ethyl. The R' group
/ | is a propyl group. For Ketones we add an
H H-C-H -one suffix to the end thus making the
| name of this compound ethylpropanone.
H-C-H
|
H-C-H
|
H
H H H This molecule's R group is a methyl group.
| | | The first part of this molecule's
H-C-C-C=O name is therefore 'methyl'.The R' group is
| | | a propyl group. For Esters we add an
H H O '-oate' suffix thus making the name
| methylpropanoate.
H-C-H
|
H
Well, that was huge. That's about all I know about naming organic compounds with functional groups. In the next section I want to discuss cyclic compounds (I forgot them in section 3) and compounds with multiple function groups.
Back to the contents:On to the next section
Professor_Pi helped me out alot with this writeup. Thankyou very much.