IUPAC System of Nomenclature of Organic Compounds

Introduction

The International Union of Pure and Applied Chemistry (IUPAC) provides a standardized system for naming chemical compounds. This system ensures clarity, consistency, and international acceptance. Understanding IUPAC nomenclature is essential to study organic chemistry. Organic chemistry serves as the backbone of complex scientific disciplines ranging from medicine to material science. IUPAC forms a set of rules for systematic nomenclature of organic compounds. In this article we will discuss about common and IUPAC systems of nomenclature of organic compounds.

Common name system

Common names of organic compound are known as trivial names. These names are used in day-to-day conversation, historical context and certain industries. Common names are not standardized like IUPAC names but they are convenient to use. Common names are given on the basis of natural occurrence, on scientist or researchers name or their characteristic properties or function. For example, Grignard reagent is named in honour of French chemist Victor Grignard. Formaldehyde is named for its simplest aldehyde structure derived from the Latin word formica (means ant).

Common names lack the standardized rules and conventions of IUPAC nomenclature which leads to inconsistencies and confusion. Common names may be ambiguous or imprecise leading to misunderstanding or misinterpretations of the intended compound. This nomenclature system is useful only in well known or frequently encountered compounds. It is difficult to name the lesser known or newly synthesized compounds with the substance. Common names are based on the local languages which makes confusion among speakers of different languages.

IUPAC nomenclature

This is a method of naming for organic compounds recommended by the International Union of Pure and Applied Chemistry (IUPAC). In IUPAC name, there are 4 parts of a name, prefix, word root, bond and functional group. Each part of the IUPAC name gives some information about the organic compound. There is a general format for IUPAC name is,

Prefix + word root + primary suffix + secondary suffix + substituent + carbon chain + bond + functional group

Word root

It gives the information about parent carbon chain, which is the longest continuous chain of carbon atoms, whether it contains any functional groups or multiple bonds.

Suffix

The suffix in IUPAC nomenclature is usually a functional group which follows the root of the name. They further divided as a primary suffix and a secondary suffix.

Primary suffix

It is written immediately after a root word. It provides information about the carbon-to-carbon bond in parent carbon chain.

Secondary suffix

It is written after the primary suffix. It provides information about the parent or main functional group of compounds.

Prefix

In IUPAC nomenclature, prefix is added to the root word. The prefix provides information about the any substituent group attached to the parent carbon chain. It also provides information about cyclic or acyclic nature of the compound.

If compound contain polyfunctional group, functional group can be used as prefix. For example, -OH as hydroxy-, -CN as cyano-.

General steps for IUPAC nomenclature

Identify the Longest Carbon Chain

• Locate the longest continuous carbon chain (parent chain) in the compound.
• The parent chain determines the root name.

Number the Carbon Atoms

• Assign the lowest possible numbers to the carbon atoms in the parent chain.
• Prioritize functional groups and substituents when numbering.

Name Substituents

• Identify and name any substituent groups (branches) attached to the parent chain.
• Use prefixes like methyl, ethyl, etc.

Locate Functional Groups

• Identify the functional group(s) present (e.g., alkanes, alcohols, etc.).
• Include them in the name as prefixes or suffixes.

Assemble the Name

• Combine the root name of the parent chain, substituent names, and functional group names.
• Arrange them alphabetically.

Use Prefixes and Suffixes

• Use prefixes (di-, tri-, tetra-) for multiple identical substituents.
• Add suffixes (-ol, -one, -oic acid) for functional groups.

Check for Special Cases

• Some compounds have unique names (e.g., water, ammonia).
• Learn exceptions (e.g., ethanol instead of ethyl alcohol).

Priority order of functional group

If compound contain polyfunctional group, functional group of higher priority is considered as principal functional group and other functional groups are considered as substituents. The priority order of functional groups is as follows,

Carboxylic acid (-COOH) > sulphonic acid (-SO3H) > acid anhydride (-COO-) > ester (-COX) > acid chloride (-COCl) > amide > (-CONH2) > nitrile (-CN) > aldehyde (-CHO) > ketone (-CO-) > alcohol (-OH) > amine (-NH2).

Summary

IUPAC nomenclature provides a universal language for naming compounds, ensuring clarity and precision in scientific communication. By using this scientific approach we can accurately describe molecular structures and facilitate collaboration across disciplines.

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