Organic Compounds are those which have Carbon-Hydrogen or Carbon-Carbon bonds. Chemistry is studied under three branches Organic, Inorganic, and Physical Chemistry with each dealing with different types of topics.
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What is Nomenclature of Organic Compounds?
The procedure of naming both living and non-living things is known as nomenclature. The word is derived from the Latin words “nomen” (name) and “calare” meaning “call.” Different compounds are named according to standards that have been agreed upon globally. But it might range from following severe regulations to adopting the everyday language. When dealing with the process of nomenclature for organic compounds, then this process of nomenclature is referred to as ” Nomenclature of Organic Compounds” which we will discuss in this article in detail.
Need of Nomenclature for Organic Compounds
In the early days, when there is no guidelines for naming conventions of organic compounds, there was a lot of confusion among chemistry scholars as they can’t communicate with the names of organic compounds. Thus, in 1919 IUPAC was founded to standardize various things such as atomic weight, melting point, boiling point, and various other properties of elements. Other than this they were also tasked to create the guideline for the naming convention scheme which now is known as IUPAC Nomenclature.
IUPAC System of Nomenclature
Guideline for the systematic nomenclature of organic compounds given by the organisation “International Union of Pure and Applied Chemistry”(often abbreviated to IUPAC) is known as “IUPAC nomenclature of organic compounds”.
The international organization in charge of standardizing the atomic weights, symbols, nomenclature, etc. of different substances is known as IUPAC. It creates and updates this data to support scientists and researchers around the world. The IUPAC nomenclature for inorganic and organic chemicals was developed by this organization.
IUPAC Nomenclature
Every scientist must follow a set of regulations under the IUPAC nomenclature of organic chemistry in order to name compounds that belong to specific groups for better communication of information. In IUPAC Nomenclature, there are three key components: Root word, Suffix and Prefix. With the help of these three components and rules from IUPAC, we can name any organic compound under the blue sky with ease. Let’s learn about these components of Nomenclature in detail.
Root Word
The number of carbon atoms in the major chain i.e., the longest conceivable chain of carbon atoms, is indicated by the root word. Greek number roots are used for chains of five or more carbon atoms, whereas specific word roots (based on the common names of alkanes) are used for chains of one to four carbon atoms. For instance, the terms “meth” and “non” denote one-carbon atom chain and nine-carbon atoms, respectively, in an organic compound. The following table shows the first twenty root words for the carbon chain.
| Carbon in Chain | Root Word | Carbon in Chain | Root Word |
|---|---|---|---|
| 1 | Meth- | 11 | Undec- |
| 2 | Eth- | 12 | Dodec- |
| 3 | Prop- | 13 | Tridec- |
| 4 | But- | 14 | Tetradec- |
| 5 | Pent- | 15 | Pentadec- |
| 6 | Hex- | 16 | Hexadec- |
| 7 | Hept- | 17 | Heptadec- |
| 8 | Oct- | 18 | Octadec- |
| 9 | Non- | 19 | Nonadec- |
| 10 | Dec- | 20 | Icos- |
Suffix
In IUPAC nomenclature, the suffix comes after the root name and designates the functional group to which it belongs. It is further divided into primary and secondary categories. The root word is followed directly by the main suffix.
Primary Suffix
A main suffix is a suffix that is used to indicate whether the carbon atoms in the parent chain are saturated or unsaturated. Below is the basic primary suffix,
| Nature of Carbon Chain | Primary Suffix | General Name |
|---|---|---|
| Saturated (C–C) | -ane | Alkane |
| Unsaturated, containing one double bond (C=C) | -ene | Alkene |
| Unsaturated, containing one triple bond (C≡C) | -yne | Alkyne |
Secondary Suffix
A secondary suffix is a suffix that is used to indicate the main functional group’s nature in a compound.
| Class of Organic Compounds | Functional Group | Secondary Suffix |
|---|---|---|
| Alcohol | R-OH | -ol |
| Aldehyde | R-CHO | -al |
| Amine | R-NH₂ | -amine |
| Carboxylic Acid | R-COOH | -oic acid |
| Ester | R-COOR’ | -oate |
| Ether | R-O-R’ | -ether |
| Ketone | R-CO-R’ | -one |
| Alkene | R₂C=CR₂ | -ene |
| Alkyne | RC≡CR’ | -yne |
| Halide | R-X | -ide |
| Amide | R-CO-NH₂ | -amide |
| Nitrile | R-CN | -nitrile |
| Thiol | R-SH | -thiol |
| Sulfonic Acid | R-SO₃H | -sulfonic acid |
| Sulfide | R-S-R’ | -thio |
| Peroxide | R-O-O-R’ | -peroxide |
| Imine | R-N=CR’ | -imine |
| Isocyanate | R-N=C=O | -isocyanate |
| Isothiocyanate | R-N=C=S | -isothiocyanate |
| Alkyl Halide | R-X | -yl halide |
| Phosphine | R₃P | -phosphine |
| Sulfate | R-O-SO₃H | -sulfate |
| Thioester | R-CO-SR’ | -thioate |
| Thioether | R-S-R’ | -thioether |
It is to be noted that when adding a secondary suffix to a primary suffix if the secondary suffix starts with “a,” I “o,” “u,” or “y,” the main suffix’s terminal “e” is dropped.
| Organic compounds | Word root | Primary suffix | Secondary suffix | IUPAC name(Word root + Primary suffix + Secondary suffix) |
|---|---|---|---|---|
| CH3CH2OH | Eth | -ane | -ol | Ethanol |
| CH3CH2CHO | Prop | -ane | -al | Propanal |
| CH3CH2COOH | Prop | -ane | -oic acid | Propanoic acid |
| CH3CH2CH2NH | Prop | -ane | -amine | Propanamine |
| CH3CH2CN | Prop | -ane | -nitrile | Propanenitrile |
Prefix
Under this nomenclature, a prefix is placed in front of the root names of compounds. Prefix usage is extremely beneficial because it demonstrates the presence of side chains and substituent groups in an organic compound. These prefixes shed light on a compound’s acyclic and cyclic properties.
Primary Prefix
To distinguish between cyclic and acyclic compounds, the main prefix cyclo is used.
Secondary Prefix
Certain characteristic groups are not regarded as functional groups or secondary suffixes in the IUPAC nomenclature system. These are designated by secondary prefixes and are thought of as substituents. Below are a few secondary prefixes.
| Substituent Group | Secondary Prefix | Substituent Group | Secondary Prefix |
|---|---|---|---|
| −F | Fluoro | −OH | Hydroxy |
| −NO2 | Nitro | −COOH | Carboxy |
| −Cl | Chloro | −NH2 | Amino |
| −CH3 | Methyl | −CN | Cyano |
| −Br | Bromo | −CHO | Formyl |
| –C2H5 | Ethyl | −C6H5 | Phenyl |
| −I | Iodo | −COCH3 | Acetyl |
| −OCH3 | Methoxy | −N(CH3)2 | Dimethylamino |
| −NO | Nitroso | −CONH2 | Amide |
| –OC2H5 | Ethoxy | −COCl | Acyl chloride |
Methods for IUPAC Nomenclature
To write the IUPAC name for any given structure, we can use the following steps:
Step 1: Identify the longest carbon chain.
Look for the longest continuous chain of carbon atoms in the molecule i.e., the parent chain that can be a straight or branched chain, or it can also be a cyclic structure.
Step 2: Identify and name the substituent groups.
Substituents are functional groups or atoms attached to the parent chain. Identify and name these substituents, which are often named prefixes. Common substituents include methyl, ethyl, chloro, bromo, etc.
Step 3: Assign the main functional group.
Determine the main functional group present in the compound. This is usually the highest-priority group according to the IUPAC rules.
-COOH > -CHO > -C=O > -OH > -C≡C- > -C=C- > -C-C-
Step 4: Number the carbon atoms.
Number the carbon atoms in the parent chain, starting from the end that gives the lowest number to the substituents. If there is a choice, give priority to the functional group over the substituents. Numbering should provide the lowest set of locants to the substituents and functional groups.
Step 5: Combine the names
Combine the names of the substituents, the parent chain, and the functional group, following specific naming conventions. Use hyphens to separate numbers and letters, and commas to separate numbers.
Step 6: Add prefixes and suffixes
Add prefixes and suffixes to the name to indicate additional information about the compound, such as stereochemistry, multiple bonds, etc. These may include terms like cis, trans, iso, neo, cyclo, di, tri, etc.
Step 7: Check the final name
Double-check the final name for accuracy and adherence to the IUPAC naming rules. Make sure that the name is clear, unambiguous, and correctly represents the structure of the compound.
IUPAC Nomenclature of Some Organic Compounds
There are various different organic compounds, thus we need to know all the general methods for the naming.
IUPAC Name of Alkanes
Alkanes have a general formula that is CnH2n+2. Alkanes are typically denoted by the suffix “ane.” Methane for the compound CH4 and butane for the compound C4H10 are examples of alkanes that should be named according to IUPAC criteria.
IUPAC Name of Alkenes
Alkenes have the general formula CnH2n. Alkenes are classified by the suffix “ene” according to IUPAC rules. Examples of the nomenclature of alkenes include the names ethene and propene, which are used to denote the compounds produced by C2H4 and C3H6, respectively.
IUPAC Name of Alkynes
Alkynes have the general formula CnH2n-2. Alkynes are typically denoted by the suffix “yne.” Ethyne, which is used to denote the molecule represented by C2H2, is an example of the IUPAC nomenclature for alkynes.
IUPAC Name of Halogens
| Halogen | Symbol | Prefix |
|---|---|---|
| Florine | F | Fluoro |
| Chlorine | Cl | Chloro |
| Bromine | Br | Bromo |
| Iodine | I | Iodo |
To name compounds containing halogen atoms, we use the prefix halogen in front of the remaining name of the compound. If there is more than one halogen molecule attached to the given structure, then we use alphabetical order to decide which prefix comes first.
For example, let’s consider the structure of Cl – CH2 – CH(Cl) – CH2 – CH2 – Br. As there are four carbon atoms and three halogen molecules, thus root word is bute. Thus, the name of a given structure is 1,2-dichloro-4-bromobutane.
IUPAC Name of Alcohol
Alcohol: The suffix “-ane/ene” is replaced with “-anol/enol” while naming alcohols. The suffix is expanded to include a suitable prefix if there are multiple hydroxyl groups i.e., for two hydroxyl groups, we use diol, for three we use triol, and so on.
For example, we have given a structure, CH3(CH2)4OH. As there are 5 carbon atoms in this structure, the root word for this structure is pent, and there is only one hydroxyl group. Thus, the IUPAC name of the given structure is Pentan-1-ol OR 1-Pentanol.
IUPAC Name of Ethers
Ethers generally have common names. Two alkyl groups are linked to an oxygen atom in order to find that, the names are then arranged alphabetically with spaces between them. The word “ether” follows them. Additionally, if both alkyl groups are identical, the prefix “di-” is used. This group includes substances like diethyl ether, ethyl methyl ether, etc.
For example, CH3 – CH2 – O – CH2 – CH2 – CH3.
Oxygen splits the structure into two parts, one with two carbon atoms, and another with three carbon atoms. Thus, the IUPAC name of this structure is ethyl propyl ether OR ethoxy propane.
IUPAC Name of Aldehyde and Carboxylic Acid
Both aldehyde and carboxylic acids can be named similar to alcohols. Let’s consider an example to see how to name these compounds i.e., CH3-CH(Cl)-CH2-CH2-CHO. As there are five carbon atoms and two functional groups i.e., aldehyde and chloro. Thus, the name of the given structure is 4-chloropentan-1-al.
Similarly, in CH3-CH2-CH2-COOH there are four carbon atoms, and only one functional group i.e., -COOH. Thus, the name of the compound is buntan-1-oic acid.
IUPAC Name of Ketones
The carbon chain containing the ketone functional group ( C=O) is named by the suffix -one in the parent chain. The naming of the longest carbon chain should be done in such a way that the carbon-containing ketone functional group gets the lowest possible number. For Example in CH3-CH2-CH2-CO-CH3, the CO is at the second position when numbered from right to left and the carbon chain is of 5 Carbon atoms, hence the compound is named as Pentane-2-One.
IUPAC Name of Ester
Esters are organic compounds that have the general formula of RCOOR’. Here, R is the smaller carbon chain and it will be named alkyl, and R’ is a longer carbon chain it has the suffix -oate. For Example, in CH3-CH2-CH2-C(=O)-O-CH2-CH3 counting from right to left -CH2CH3 is ethyl, and CH3-CH2-CH2-C(=O)-O has four carbons hence it will be butanoate. Hence, the name of the compound will be Ethyl Butanoate.
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Solved Examples on Nomenclature of Organic Compounds
Example 1: Write the name of the given organic compound.
Solution:
Word root: Prop
Prefix: methyl
Primary suffix: -ane
Secondary suffix: -ol
Thus, IUPAC name of the compound is,
2-methyl-propane-1-ol
Example 2: Write the name of the given organic compound.
Solution:
Word root: Pent
Primary suffix: -ane
Secondary suffix: -ol
Thus, IUPAC name of the compound is,
pentan-2-ol
Example 3: Write the name of the given organic compound.
Solution:
Word root: Pent
Prefix: methyl
Primary suffix: -ane
Thus, IUPAC name of the compound is,
3-methylpentane.
Example 4: Write the name of the given organic compound.
Solution:
Word root: Pent
Prefix: methyl
Primary suffix: -ane
Secondary suffix: -nal
Thus, IUPAC name of the compound is,
2-methylpentanal.
FAQs on Nomenclature of Organic Compounds
Question 1: What do you mean by IUPAC?
Answer:
International Union of Pure and Applied Chemistry is known as IUPAC. In order to replace the International Congress of Applied Chemistry, it was established in 1919.
Question 2: What is Nomenclature?
Answer:
Nomenclature is the system of naming chemical compounds. It provides a standardized way to assign names to different compounds based on their molecular structure and composition.
Q3: Why is Nomenclature important in Organic Chemistry?
Answer:
Nomenclature is essential in organic chemistry because it allows chemistry scholars to communicate effectively and unambiguously about different organic compounds. By following a set of rules and conventions, scholars and chemistry enthusiasts can name compounds in a consistent and systematic manner, which facilitates the understanding and identification of various organic substances.
Q4: What are IUPAC Names?
Answer:
Names that follow the IUPAC guidelines are called IUPAC names.
Q5: What is the need for IUPAC Nomenclature?
Answer:
The nomenclature IUPAC initiative aims to establish a global standard for identifying substances to communicate effectively. The system’s goal is to provide each structure a distinct and clear name and to compare each name to a distinct and clear structure.
Q6: What are some common Functional Groups and their Suffixes in Organic Chemistry?
Answer:
Here are some common functional groups and their corresponding suffixes:
Functional Group Suffix Alkane -ane Alkene -ene Alkyne -yne Alcohol -ol Aldehyde -al Ketone -one Carboxylic Acid -oic acid Ester -ate Amine -amine Amide -amide Ether -ether
Q7: What is the IUPAC Priority Order?
Answer:
The priority order for functional groups is
-COOH > -CHO > -C=O > -OH > -C≡C- > -C=C- > -C-C-
Q8: What is the IUPAC name of Acetone?
Answer:
IUPAC name of acetone is propan-2-one.
Q9: What is the IUPAC name of Acetic Acid?
Answer:
IUPAC name of acetic acid is ethan-1-oic acid.
Q10: What is the IUPAC name of Acetylene?
Answer:
IUPAC name of acetylene is eth-1-yne.
Q11: What is the IUPAC name of Neopentane?
Answer:
IUPAC name of Neopentane is 2,2-dimethylpropane.