Organic Compounds: Classification, Properties and Sample Questions

The compounds which contain carbon in their molecule in any state viz solid, liquid, or gaseous state are known as organic compounds. There are a large number of chemical compounds which are organic compounds, so for a better study of each of them, organic compounds have been systematically classified.

Read Also: Carbon and Its Compounds

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Organic Compound

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The compounds that mainly contain carbon or carbon atoms which can covalently bond with 4 more carbon or hydrogen atoms or sometimes with other atoms like nitrogen or oxygen and are mainly formed due to natural processes of living beings are known as organic compounds. Proteins and hydrocarbons are the best examples of organic compounds which can produce long chain and complex structures.

Organic compounds which are made from these molecules are the basis of chemical reactions occurring in plant and animal cells. These reactions are the reason behind the energy required to produce food, replicate, and many other life-related natural processes.

Organic compounds can be majorly classified based on Functional groups of homologous series.

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Classification of organic compounds

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Classification of organic compounds

These organic compounds can be studied or represented in many different formats like Lewis’s structure, structural formulas, and space-filled models. Almost all the organic compounds contain hydrogen in their molecules as they complete the empty spaces which remain vacant to complete four bonds of the carbon atom. However, the carbon atom mostly combines with other carbon atoms and hydrogen to complete the bond. Sometimes other chemicals like phosphorus, oxygen, and nitrogen are also bound to carbon. Some of the carbon compounds like carbon monoxide, carbon dioxide, cyanides(-CN), cyanates, etc are not considered organic compounds despite the presence of carbon atoms. Mass spectra are used to detect the organic compounds. Some common examples of organic compounds are benzoic acid, propanoic acid, amines, butanoic acids, malonic acids, VOC, diethyl malonate, etc. These are used in daily lives for different purposes.  

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Functional Groups 

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An atom or a group of atoms that are joined together in specific manners and responsible for characteristic properties of organic compounds are functional groups. Some examples are a carboxylic acid group (-COOH), aldehyde group (-CHO), hydroxyl group (-OH), etc.

Functional Groups

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Homologous Series 

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A series or a group of organic compounds that differ from each other only by a fixed unit are homologous series. The members of this series are known as homologous. The general formula can be used to represent a homologous series where each member differs from the other by -CH2 group. Some examples of homologous series in organic chemistry are alkenes, alkanes, alkynes, alkanols, haloalkanes, amines, etc.

The picture above represents a homologous series of alkanes.

Some major classifications of organic compounds are described below:

1. Open Chain or Acyclic Compounds: Also known as aliphatic compounds, they have straight-chained or branched structures. For example Isobutane, Ethane, Acetic Acid, Acetaldehyde, etc.

Open Chain or Acyclic Compounds

2. Closed Chain or Alicyclic Compounds: These compounds contain carbon atoms in the form of a ring. When only carbon atoms are present, they are homocyclic and when other than carbon are present, they are heterocyclic. For example cyclopropane, cyclohexene, cyclohexane, tetrahydrofuran, etc.

Closed Chain or Alicyclic Compounds

3. Aromatic Compounds: Aromatic compounds are compounds of special types which contain benzene and some other ring-related compounds. They can have heteroatoms in a ring, similar to alicyclic compounds. These compounds are also called heterocyclic aromatic compounds. For example Benzoic aromatic compounds like Aniline, Naphthalene, Benzene, etc.

Aromatic Compounds

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Commonly Used Organic Compounds

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1. Benzoic Acid: 

Benzoic acid is an aromatic carboxylic compound. These are used in the manufacture of perfumes, dyes, insect repellents, etc.

Physical properties:

• Molar mass: 122.12 g/mol

• Melting Point: 122.3°C

• Boiling Point: 249.2°C
• Density: 1.27 g/ cm³

Chemical Properties:

• Heat Capacity: 146.7 J/mol.K

• Flash Point: 121.5 °C

2. Benzdehoic Alyde: 

Benzoic Aldehyde also known as benzaldehyde is an aromatic carbaldehyde compound. A carbaldehyde group is attached to a benzene ring in it. It is used in perfume making and as a flavoring agent.

Physical Properties:

• Melting Point: -26 °C
• Boiling Point: 179 °C
• Colorless

Chemical Properties:

• Flash Point: 145°F
• The heat of combustion: 3525 KJ/mol
• The heat of vaporization: 42.5 KJ/mol

3. Propanoic Acid: 

Propanoic Acid is a 3-carbon saturated molecule that contains one carboxylic group attached to the carbon. They are used as an antifungal drug.

Physical Properties:

• Melting Point: -20.7 degrees Celsius
• Boiling Point: 141.1 degrees Celsius

Chemical Properties:

• Flash Point: 130°F
• The heat of combustion: 1528.3 KJ/mol
• The heat of vaporization: 418.7 KJ/mol

4. Butanoic Acid: 

Butanoic Acid contains one carboxyl group attached with one carbon atom. Butanoic acid is also known as butyric acid. They are used as food additives.

Physical Properties:

• Melting Point: -5.7 degrees Celsius
• Boiling Point: 326.3°F

Chemical Properties:

• Flash Point: 170°F
• The heat of combustion: 521.87 Kg cal/gm
• The heat of vaporization: 40.45 KJ/mol

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Things to Remember

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• Organic compounds are compounds having carbon and carbon covalently bonded with other compounds
• Organic compounds can be classified as open chain and cyclic.
• Some commonly used functional groups of organic compounds are: carboxyllic acid, alcohol, ester, ammonia
• Homologous series are formed with compounds having similar structures but different number of carbon atoms

Read More: Versatile Nature of Carbon

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Sample Questions

Ques. Define heterocyclic compounds with some examples. (1 mark)

Ques. State some properties of organic compounds. (1 mark)

Ques. Are organic compounds useful? Why? (1 mark)

Ques. Write some materials used in daily life made using organic compounds. (1 mark)