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Organic Chemistry Nomenclature

The main function of chemical nomenclature is to make the person who hears or reads a chemical name is under no doubts as to which chemical compound it refers, each name should refer to a single substance.

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Chemical Nomenclature Rules

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1. Compositional nomenclature

  • This term is used in the present recommendations to denote name constructions which are based solely on the composition of the substances or species being named, as opposed to systems involving structural information.
  • One such construction is that of a generalized stoichiometric name. The names of components which may themselves be elements or composite entities (such as polyatomic ions) are listed with multiplicative prefixes giving the overall stoichiometry of the compound.
  • If there are two or more components, they are formally divided into two classes, the electropositive and the electronegative components.
  • In this aspect, the names are like traditional salt names although there is no implication about the chemical nature of the species being named.
  • The ordered rules are then required to specify the ordering of components, the use of multiplicative prefixes, and the proper endings for the names of the electronegative components.
Examples
1. Trioxygen, O3
2. Sodium chloride, NaCl
3. Phosphorus trichloride, PCl3

2. Substitutive nomenclature

  • Substitutive nomenclature is used widely for organic compounds and is based on the concept of a parent hydride modified by substitution of hydrogen atoms by atoms and /or groups.
  • Many of the cases used for naming organic ligands in the nomenclature of coordination and organometallic compounds, even though this is an overall additive system.
  • It is also used for naming compounds formally derived from the hydrides of certain elements in groups 13–17 of the periodic table.
  • Like carbon, these elements form chains and rings which can have many derivatives, and the system avoids the necessity for specifying the location of the hydrogen atoms of the parent hydride.
  • Rules are required to name main or parent compounds and substituents, to provide an order of citation of substituent names, and to specify the positions of attachment of substituents.
Examples
1. 1, 1-difluorotrisilane, SiH3SiH2SiHF2
2. Trichlorophosphane, PCl3

3. Additive nomenclature

  • Additive nomenclature explains a compound or species as a combination of a central atom or central atoms with associated ligands.
  • The particular additive system used for coordination compounds is sometimes known as coordination nomenclature although it may be used for much wider classes of compounds, as demonstrated for inorganic acids and organometallic compounds and for a large number of simple molecules and ions.
  • Another additive system is well suited for naming chains and rings.

Rules within this nomenclature provide ligand names and guidelines for the order of citation of ligand names and central atom names, designation of charge or unpaired electrons on species, designation of point(s) of ligation in complicated ligands, designation of spatial relationships, etc.Examples
1. PCl3, trichloridophosphorus
2. [CoCl3 (NH3)3], triamminetrichloridocobalt

Nomenclature Organic Chemistry

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The naming of organic chemistry is an important aspect in the study of organic chemistry as there number is very large and variety of molecular structures exists in their molecules. The field has become more complex on account of the phenomenon of isomerism.

There are two main systems of nomenclature of organic compounds
  1. Trivial system
  2. IUPAC system

Trivial System of Nomenclature in Organic Chemistry

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Trivial name is a non systematic name or vernacular name of an organic compound. There is no specific rules about the trivial name of the compound.

Features of Trivial system


The name of the compound will be simple like phenol, acetic acid, toluene etc. For example the following carboxylic acid is named as tartaric acid which is commonly found in tamarinds.
Carboxylic Acid
But in IUPAC system it is called as 2,3-dihydroxy-1,4-Butanedioic acid. The name is derived from root Latin or Greek words in some cases. For example in the name of formic acid, formica means distillation of ant bodies. This acid is found in venom of ant and bee stings. Hence it got the trivial name.

Drawbacks of the Trivial system
  1. There are many trivial names for a single compound. For example phenol with formula C6H6O is called as phenol, hydroxy benzene, carbolic acid etc.
  2. This type of nomenclature is restricted for few compounds in each family. For example in carboxylic acid family the first two members with formula HCOOH, CH3COOH have trivial name as formic acid and acetic acid. But there is no specific trivial name for a carboxylic acid with six carbon atoms.
  3. Similarly there is no specific guidelines for complex substituted compounds in organic chemistry.

IUPAC Rules

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In IUPAC organic nomenclature or iupac nomenclature rules each organic compound is named as a derivative of parent hydrocarbon by prefixing/suffixing the substituents along with the locants.

So the IUPAC nomenclature involves the following steps.
  1. Identification and naming of parent hydrocarbon.
  2. Numbering the chain and identifying the substituents.
  3. Classify the substituents as prefix/suffix. Some of the substituents like carboxylic acid (-COOH) will always be used as suffix only while some of the substituents like hydroxy (-OH) will be used as both prefix and suffix in according to the priority.
  4. Identifying the locants of the substituents.
  5. Arriving the final name as LOCANT+PREFIX+ROOT+LOCANT+SUFFIX

Let us see an example to understand the concept better.
  1. In according to chemical nomenclature rules the longest parent hydrocarbon has four carbon atoms. Hence the parent hydrocarbon name is butane.
  2. There are two substituents methyl and hydroxy in which hydroxy will get priority over methyl and become suffix name. Hence the chain is numbered from right to left so that the carbon containing hydroxy group gets the least number.
  3. Hence the substituent hydroxy will get 1 as locant and the two methyl groups will get 3 as locant.
  4. Hence the name of the compound is 3,3-dimethyl-1-butanol

IUPAC Rules

Chemical Nomenclature Chart

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S.No.
Formula of
Substituent
Name
(suffix)
Name
(prefix)

1 -OH ol (like in
methanol
hydroxy
2
-COOH -oic acid
(like in methanoic acid)
-
3
-NO2 - Nitro
4
-CH = CH- ene (like in ethene) -
5
-CHO -al (like in ethanal) formyl
6
-Cl - chloro
More topics in Organic Chemistry Nomenclature
Balancing Chemical Equations Organic Compounds
Functional Groups Isomers
Nomenclature Chemistry
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