Nomenclature of Compounds containing Polyfunctional Groups
Polyfunctional Compounds
Organic compounds that contain two or more functional groups are called polyfunctional compounds. Some examples of organic compounds with polyfunctional groups are given below :
Organic compounds containing polyfunctional groups examples
3-Oxobutan-1-oic acid
4-Chloro-3-methoxybutan-1-al
4-Aminopentan-2-ol
2-Amino-5-formyl-3-hydroxypentan-1-oic acid
Let us now study how such compounds are named :
Principal functional group
In a polyfunctional compound, one of the functional groups is selected as the principal functional group while all other functional groups are treated as substituents.
Functional groups according to their priorities are listed in the priority table in decreasing order i.e., Carboxylic acid with the highest priority is placed at the top while alkyne being the least in priority is placed at the bottom. The functional group which has the highest priority among all the functional groups present in an organic compound is selected as the principle functional group.
| COMPOUND NAME | FORMULA |
|---|---|
| Carboxylic acid | -COOH |
| Sulphonic acid | -SO3H |
| Ester | -COOR |
| Acid chloride | -COCl |
| Acid amides | -CONH2 |
| Nitrile | -CN |
| Aldehyde | -CHO |
| Ketone | >C=O |
| Alcohol | -OH |
| Phenol | -C6H6O |
| Thiols | -SH |
| Amines | -NH2 |
| Ether | -OR |
| Alkene | >C=C< |
| Alkyne | -C≡C- |
All functional groups other than the principal functional group present in an organic compound are called substituents.
In the following example, COOH being highest in priority is selected as the principal functional group while all others are treated as substituents.
Some of the substituents with their prefixes are given below :
| SECONDARY FUNCTIONAL GROUP | PREFIX |
|---|---|
| -X (F,Cl,Br,I) | Halo (fluoro, chloro, bromo, iodo ) |
| -OH | Hydroxy |
| -SH | Mercapto |
| -OR | Alkoxy |
| -NH2 | Amino |
| -CHO | Formyl or alkanoyl |
| -C=O | Keto or oxo |
| -COOH | Carboxy |
| -COOR | Alkoxycarbonyl or carbalkoxy |
| -COCl | Halocarbonyl or haloalkanoyl |
| -CN | Cyano |
| -CONH2 | Carbamoyl or Carboxamido |
It's time you answered a question.
Can you identify the principal functional group :
Numbering the principal chain
The principal chain present in a polyfunctional compound must be numbered in such a way that the principal functional group gets the lowest possible number followed by double bond, triple bond and substituents.
4-Chlorobut-1-ene-1,4-diol (not 1-Chlorobut-3-ene-1,4-diol)
Name the following compound by doing the correct numbering :
Remember, some groups like Cl, F, NO2 are always considered as substituents even when no other functional group is present (already discussed in nomenclature introduction ).
Alphabetical order
If two groups of the same priority occupy identical positions from either end of the parent chain, the lowest number must be assigned to the group whose prefix comes first in the alphabetical order.
More than two occurrence
When the same carbon containing functional group appears more than two times in a chain, the carbons of that functional group are not included while numbering the chain. Further, secondary suffix used in these cases is different from what we have learnt so far.
Compare :
COOH appears two times
COOH appears three times (i.e., more than two times)
Notice that the secondary suffix used in the above example is tricarboxylic acid (not trioic acid).
Secondary suffixes of different functional groups used in these cases are given below :
| FUNCTIONAL GROUP | PREFIX | SUFFIX |
|---|---|---|
| -CHO | Formyl | Carbaldehyde |
| -COOH | Carboxy | Carboxylic acid |
| -COX (X=F,Cl,Br,I) | Halocarbonyl | Carbonyl halide |
| -COOR | Alkoxycarbonyl or Carbalkoxy | Alkyl carboxylate |
| -CONH2 | Carbamoyl | Carboxamide |
| -CN | Cyano | Carbonitrile |
However, these rules are not applicable if the occurrence is not more than two times in a single chain.
Compare :
In the above example, all the three occurrences of CN are the part of the same chain. Notice that the secondary suffix carbonitrile is used.
In the above example, one of the CN groups is considered as a substituent because it is not directly attached to the parent chain. Notice that the secondary suffix nitrile is used.
Name the following compound :
Some complicated namings
The naming of some functional groups like esters, amines is somewhat complicated; hence they are discussed below separately.
Esters (R-COOR')
In case of esters, alkyl group R' comes at the beginning of the name.
Example : 1
H-COOCH3 : Methyl methanoate
Example : 2
CH3-COOCH3 : Methyl ethanoate
Amines
In secondary and tertiary amines, the prefix N-alkyl is used to denote alkyl groups.
Example : 1
CH3CH2NHCH3 : N-Methylethanamine
Example : 2
(CH3)3N : N,N-Dimethylmethanamine