Classification of Organic Compounds

Classification of Organic Compounds - Cyclic Compounds and Acyclic Compounds


What do you know about organic compounds? If we talk about in Chemistry terms, Organic compounds can be defined as any type of chemical compounds in which atoms of carbon, that could be one or more than one, are covalently linked to the other elements’ atoms. In very simple terms you can say that organic compounds are simply any chemical compounds that have carbon but it doesn’t mean that every carbon-containing compound can be known as organic, for e.g. cyanides, carbonates and carbides. The best example of the simplest organic compound is Methane. Few examples of Organic compounds are cyclohexane, ethyne, ethane and ethane.


Organic Compounds can be classified on two bases. Firstly we will talk about organic compounds which are based on “Structure” and secondly, we will discuss the organic compounds which are based on “Function”. Now we will study these classifications of organic compounds in detail.

1. Classification of organic compounds based on Structure

(i) Acyclic or open chain compounds
(ii) Cyclic or closed chain compounds

(i) Acyclic or open-chain compounds:- 

Acyclic compounds are just opposite to cyclic compounds because their molecules don’t form any ring. It is called open chain compounds because they have a linear structure. The best examples of these compounds are acyclic aliphatic compounds and alkanes. Open-chain compounds can be understood by straight-chain compounds and branched-chain compounds. In the straight-chain compounds don’t have any side chains but branched-chain compounds’ atoms have the straight chain and one or more than one side chains are attached to it. 

(ii) Cyclic or closed-chain compounds:- 

Cyclic compounds are also known as “Ring compounds”. As its second name suggests, cyclic compounds are those kinds of compounds where one or more than one number of atoms get connected to form a closed ring. It is not mandatory that every ring of these compounds is to be of the same size.

Cyclic or closed-chain compounds

Cyclic or closed-chain compounds always have a prior place in human being’s day to day life as human encounters these compounds on a daily basis. They are also categorized into two divisions. The first division is about “Heterocyclic” and second division is about “Homocyclic”. Now we will discuss these categories one by one.

(a) Heterocyclic:-

Heterocyclic compounds are a kind of cyclic compounds in which the ring structure exists. We can understand these compounds in very simple definition as it is like of any other dominant branch of organic compounds in which two or more than two atoms join in the ring shape in their molecules. Although they have atoms of carbon, it must be noticed that at least one atom of another element also exists. The very familiar examples of these compounds are synthetic dyes, nucleic acids and most of the drugs. 

(b) Homocyclic:- 

 If we talk about organic chemistry Homocyclic compounds are the type of cyclic compounds, unlike heterocyclic, in which the ring structure is formed by the atoms. This ring structure is made up of the same elements’ atoms and this element is the carbon. This is called as Carbocyclic compounds. No element other than carbon can exist in this compound. Although in inorganic chemistry homocyclic compounds have ring structures which have been formed by diff-diff elements’ atom like boron, sulphur, phosphorous and so on. The best examples of this compound are naphthalene, tetracene, benzene and so on.


Heterocyclic compounds are divided into two broad categories which are named as Alicyclic heterocyclic compounds and Aromatic heterocyclic compounds. Now, we will discuss these categories in brief.

  • Alicyclic heterocyclic compounds:-

  • We can understand these compounds by simple lines. Ring structures of these compounds have one or more one heteroatoms. We can understand these compounds by a few examples which are tetrahydrothiophene, tetrahydrofuran and so on.

  • Aromatic heterocyclic compounds:-

  •   These compounds can be easily defined by simple understanding. Unlike Alicyclic heterocyclic compounds, molecules of these compounds have one or more than one heteroatoms. Example of these compounds is thiophene, furan and so on.

    Homocyclic or carbocyclic compounds

    Homocyclic or carbocyclic compounds are basically divided into two compounds. The first compound is known as Alicyclic compound and second is known as Aromatic compound. Now we will discuss these compounds in detail.

  • Alicyclic Compound:-

  •  The alicyclic compound is that kind of compound which is aliphatic and cyclic too. This compound has one or more than one all-carbon rings that can be saturated or unsaturated. The bonds which exist in pair of atoms can be any type of bond like single, double or triple.

  • Aromatic Compound:-

  •  Aromatic compounds are those cyclic compounds which are unsaturated, unlike alicyclic compound which are either saturated or unsaturated. These compounds are also called as aromatics or arenas. They are pleasant in the smell as their Greek meaning suggests which is “aroma”. These compounds can be distinguished by one or more than one planar rings of atoms linked by covalent bonds of two different types. A few examples of these compounds are benzene and toluene.

    Aromatic Compound

    Aromatic compounds have a distinctive stability and this is why they are referred to as aromaticity which is majorly concerned with odour. Now we will discuss the classification of these compounds which are basically Benzenoid Aromatic Compounds and Non-Benzenoid Aromatic compounds. Further, we will discuss them in detail.

  • Benzenoid Aromatic Compounds:-

  • These aromatic compounds are mainly obtained from the benzene. These compounds are distinguished by the existence of one or more than one isolated or fused benzene rings additionally their derivatives in the structure. These compounds can be arranged as Monocyclic, Bicyclic and Tricyclic on the basis of the number of benzene rings which are fused together in the structure. In bicyclic and tricyclic compounds there are two or more than two rings present in the structure. A few examples of these compounds are Phenanthrene, Naphthalene, Anthracene and so on.

  • Non-benzenoid Aromatic compounds:-

  •  These aromatic compounds consist of other unsaturated rings instead of benzene rings. These aromatic compounds have special stability. Some examples of these compounds are Tropolone and Azulene.

    2. Classification of an organic compound on the basis of Functional Group:-

     A functional group can be defined as a process in which a molecule receives its characteristics chemical properties by one or group of atoms which exist in the molecule. Now we must understand why we need to classify organic compounds on the basis of functional groups. The answer is very simple because it classifies the chemical behaviour of an organic compound. We need to understand that the nature of functional groups draws impacts on the reactions of compounds and at some level their physical properties. There are numerous organic reactions, which involve functional group transformation, have no effect on the rest of the molecules. There are so many examples in the functional group case such as the carboxylic acid group (-COOH), the hydroxyl group (-OH) and the aldehyde group (-CHO). 

    Amides (Alkanamides)AmidIsocyanides– N      C (Isocyano)
    Alcohols (Alkanols)–OH (Hydroxy)Olefins/Alkenes (ene)
    Amines (Amino)Ketones (Alkanones) (Carbonyl)
    Acetylenes/Alkynes (yne)Nitro compounds (Nitroalkanes)(Nitro) ¯
    Acid anhydrides(Alkanoic anhydrides)(Anhydride)Esters (Alkylalkanoates)(Ester)
    Aldehydes (Alkanals)(Aldehydic)Alkyl Halides
    Acid halides (Alkanoyl halids)(Acylhalide)Cyanides/Nitriles (Alkanenitrile)(Cyano)
    Ethers (Alkoxyalkanes)Carboxylic acid(Alkanoic acid) (Carboxyl)