To increase the range of application of hydrocarbons we need to add other groups to it, to give the needed properties. We will represent these organic compounds as RX − "R" will be the hydrocarbon component and X is a group that replaces a hydrogen atom, which we will call the functional group. Example: CH3Cl.
The first item in our agenda will be to understand the system used to name these organic compounds. For this the hydrocarbon component R will be known as the alkyl radical, and following the system for Inorganic compounds we will name it methyl chloride (like sodium chloride for NaCl). The early chemists used this approach for other organic compounds. Example CH3OH was known as methyl alcohol, as the known alcohol at that time was found to have the "OH" functional group. However others chose to name it methanol.
As the number of organic compounds prepared increases personal preference has given to chaos in naming the compounds. Eventually enough is enough. Chemists want to go back to doing chemistry and be able to communicate clearly. So we all agreed to accept a standard system known as the IUPAC nomenclature.
IUPAC NOMENCLATURE
The first principle is to give each group a family name.
| FUNCTIONAL GROUP |
IUPAC NOMENCLATURE | EXAMPLE | |
|---|---|---|---|
| R−F R−Cl R−Br R−I | Alkyl halide | Alkyl fluoride Alkyl chloride Alkyl bromide Alkyl iodide |
CH3F Methyl fluoride CH3Cl Methyl chloride CH3Br Methyl bromide CH3I Methyl iodide |
| R−OH | Alcohol | Alkanol | CH3OH Methanol |
| R−O−R' | Ether We can named it as an ether of as a RO− substituent (alkoxy). The latter comes in very useful for complicated ether. |
CH3−O−CH2CH3 Ethyl methyl ether, or Methoxyethane. | |
| R−NH2 R−NH−R' R−N(R')(R") |
Amine IUPAC did not give amine a family name. Instead it preferred to name it as a substituent to the alkane, an aminoalkane. Chemical Abstract did gave it a family name. |
CH3CH2CH (NH2) CH3
2-aminobutane CH3CH2CH [NH(Et)] CH3 2-(ethylamino)-butane CH3CH2CH [N(Et)(Pr)] CH3 2-(ethylpropylamino)-butane | |
| R−C−H ║ O | Aldehyde | alkanal | CH3−C−H Ethanal ║ O |
| R−C−R' ║ O | Ketone | alkanone | CH3−C−CH3 2-propanone ║ O |
| R−CN | Nitrile | alkanenitrile | CH3−CN Ethanenitrile |
| R−C−OH ║ O | Acid | alkanoic acid | CH3−C−OH Ethanoic acid ║ O |
| R−C−OR' ║ O | Ester | alkanoate | CH3−C−OCH3 ║ O Methyl ethanoate |
| R−C−Cl ║ O | Acid chloride | alkanoyl chloride | CH3−C−Cl Ethanoyl chloride ║ O |
| R−C−NH2 ║ O | Amide | alkanamide | CH3−C−NH2 Ethanamide ║ O |
| HO−C−R−C−OH ║ ║ O O | Di−acid | alkanedioic acid | HO−C−(CH2)2−C−OH
║ ║ O O Butanedioic acid |
| R−C−O−C−R' ║ ║ O O | Acid anhydride | alkanoic anhydride | H−C−O−C−CH2CH3 ║ ║ O O Methanoic propanoic anhydride |
Influence of culture: In the Western culture the family name is written to the extreme right and this has crept into the nomenclature. The Chinese has it the other way round. My family name is Ng and so my name is Ng Swee Ching. For westerners I would have to write Swee Ching, Ng.
Of course the functional group is understood to be at carbon−1. However when it is somewhere other than carbon-1 it needs to be specified. Example CH3CH(OH)CH2CH3. We can name it 2−butanol (or butan−2−ol). So be very careful butanol meant that the OH group is at carbon−1.
When a compound have more than one substituent there be a need to decide which you like to be the functional group, the other group would then become a substituent. Example: Cl-CH2CH2COOH. If you consider this as an acid then the chlorine becomes a substituent. We will then name it 3−chloro−propanoic acid. Since the position of the the acid group COOH was not specified, it is understood to be at C−1.
Occasionally the Greek alphabets are used instead of numbers. It is up to the author, it does add a touch of class.
| Position | 1 | 2 | 3 | 4 | 5 | |
| Greek alphabet | α | β | γ | δ | ε | |
| Equivalent to | a | b | c | d | e |
We usually stop at the fifth carbon (ε); not to overdo.
As a reminder: A compound can have more than one name, but a name can only represent one compound. If you find a name representing two compounds then the name is useless as it does not communicate.
Below are names for some common radicals (or substituents).
| RADICAL F− Cl− Br− I− |
NAME fluoro chloro bromo iodo |
RADICAL OH− NH2− CN− |
NAME hydroxy amino cyano |
RADICAL −COOR −CONH2 −COCl −COBr | NAME alkoxycarbonyl carbamyl chloroformyl bromoformyl |
POPULAR NAME
Here popular name means name commonly used by the general public, especially by those in the chemical industry. Chemistry is an applied science and so it must relate to the industry. It is important for chemists to recognise compounds by their popular names. Chemists cannot imprison themselves in the ivory tower. Below are a few examples.
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Tutorial 1.2
Write the IUPAC name for the following compounds.
1.
2.
3.
4.
5.
6.
Answer
CHEMICAL ABSTRACT SYSTEM
Chemical Abstract is a weekly publication tracking the latest research papers published. As such it does have to look for systems that can help it crosscheck the thousands upon thousands of compounds studied every day.
For amines the Chemical Abstract recognised amine as a family. Following the fundamental concept used by IUPAC it replaces the last "e" in alkane with amine. That is alkanamine. Of course the longest chain is chosen as the parent amine. The prefix "N" is used to denote the other alkyls attached to the amine. Ethylmethylpropyl amine will then be known as N-ethyl-N-methylpropanamine.
| PART III |
