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Organic Chemistry Nomenclature


Organic chemistry nomenclature is always a topic of great interest. The molecules that we get to see around us in al living organism makes a good deal of discussion and research objectives. For every molecule that a matter possess, providing a perfect description is very much essential. To understand these descriptions, the molecules needs to be segregated according to their molecular arrangement and bonding patterns. 

But even after these provisions, there always remain a chance of making error in identifying these molecules or naming them efficiently. There are various forms of explanation and language that we always use to describe a chemical but bringing them under one specialised naming system is what given rise to uniform nomenclature. These specific nomenclature for organic molecules help in identifying without much trouble as these are used worldwide without bias or exceptions.

Nomenclature Organic Chemistry

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Organic chemistry possess huge number of chemical molecules and everything needs to be identified and segregated properly with specific naming system so that nothing is missed or mismatched for any chemicals that we come across every day. These are done irrespective of region, language or local dialects. 

The naming system follow specific rules which helps in naming uniformly all over the chemical fraternity without bias or exceptions. Identifying molecules has become easier as for everyone who knows chemical terminology and follows these rules to segregate and specify. 

Chemical Nomenclature Rules

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The chemical nomenclature rules for organic chemistry is essential as the chemical fraternity around the world needs to know developments in the field of organic chemistry and biochemistry. The rules are easy to implement and once followed, one can identify the molecules properly and understand the reactions or thesis paper submitted by any research fellow. These can be done without worrying about the language or origin as these contemporary and accepted worldwide. 
  • Identifying the longest chain in an organic molecule is the first job 
  • Identifying the functional groups attached to these main long chain or branches which eventually form after the identification of longest chain is essential
  • Proximity of these functional groups to main chain terminals is important as well
  • Using alphabetical order and numbering of functional groups is necessary to highlight the presence of more than one functional group attached to same carbon atom 
  • The presence of double and triple bonds also plays a big role in identifying the terminals and subsequent numbering of carbon atoms and final naming of the compound

Trivial System of Nomenclature in Organic Chemistry

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The nomenclature of organic chemicals follows strict naming system to bring about semblance and uniformity. But in some specific cases or for some common molecules there is a provision of using common names which we term as trivial nomenclature. So for specific groups of molecules the use of ‘meth’ or ‘eth’ are meant for methyl or ethyl etc.

The nomenclature of these compounds where two highly unsaturated rings are fused together through two common carbon atoms, we put them under extended series of trivial names. The most important such trivial names are mentioned below. These are mainly taken from cyclic forms or benzene units. 

Parent component  Trivial form
 Anthra  Anthracene
 Benzo  Benzene
 Naphtho  Naphthalene
 Perylo  Perylene
 Acenaphtho  Acethaphthylene
 Phenanthro  Phenanthrene


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The International Union of Pure and Applied Chemistry has come out with specific rules in order to name these organic molecules in a systematic manner. Before the advent of IUPAC names there used to be trivial names or common names and since some of these are very useful and famous, were incorporated into the main IUPAC system as well.

The IUPAC name of any organic compound is divided and given specific four fields. 
  • The first of these includes names and positions of substituents 
  • The second of these contains the molecules root word 
  • The third of the series comprise of multiple bond index
  • The fourth and last of the fields explains the principle functional group
1st field             ===    2nd field          = ==    3rd field                    = ==   4th field 
[Substituents]        [Molecule root]       [Multiple bond index]      [Main functional group]

Chemical Nomenclature Chart

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The IUPAC nomenclature rules for naming organic molecules is very specific and widely used all across the series. By using these rules, a parent chain or main is identified and then the subsequent substituents (atoms, group of atoms) which are attached to the main chain. We need to specify numbers for carbon atoms in a parent chain or substituents and also use prefixes. 

The IUPAC rules are modified to an extent to allow the famous trivial names to make these rules approachable.

Prefix used for IUPAC  Number of atoms
 Meth  1
 Eth  2
 Prop  3
 But  4
 Pent  5
 Hex  6
 Hept  7
 Oct  8
 Non  9
 Dec 10

Let us now look at some alkyl groups as well. 

Names of alkyl groups  Formulas of alkyl groups 
 Methyl  -CH3
 Ethyl  -C2H5
 Propyl  -C3H7
 Butyl  -C4H9
 Isopropyl  -CH(CH3)CH3
 Isobutyl  -CH2CH(CH3)CH3