Carbon and Its Compounds

Introduction to Organic Chemistry

Organic compounds are vital for sustaining life on earth and include complex molecules such as the genetic information-bearing deoxyribonucleic acid (DNA) and proteins that constitute essential components of our blood, skin, and muscles. Organic chemicals are used to synthesise materials such as clothing, fuels, polymers, dyes, and medicines.

Around the year 1780, scientists began to distinguish organic compounds obtained from plants and animals and inorganic compounds prepared from mineral sources. A Swedish chemist, Berzelius, proposed that a ‘vital force’ was responsible for the formation of organic compounds. However, this notion was rejected in 1828 when F. Wohler synthesised an organic compound (urea) from an inorganic compound (ammonium cyanate). The pioneering synthesis of acetic acid by Kolbe (1845) and that of methane by Berthelot (1856) showed conclusively that organic compounds could be synthesised from inorganic sources in the laboratory.

As we know that carbon has a unique tendency of catenation, it binds with itself via a series of covalent bonds. This is the basis of organic chemistry.

The number of carbon compounds is so vast that there is one branch of chemistry dedicated only to the study of carbon and its compounds. This branch is known as organic chemistry.

Organic chemistry is a discipline within chemistry, which involves scientific study of structure, properties, composition, reactions, and synthesis of compounds containing carbon. These compounds can also contain nitrogen, sulphur, and halogens. The source of these organic compounds is widely spread in nature. Sources of some of the important organic compounds are given in the table below:

Source	Organic Compound Obtained From Source
Plants	Sugar, starch, cellulose, drugs
Animals	Urea, proteins, fats
Coal	Benzene, toluene, naphthalene, dyes, drugs, perfumes
Petroleum	Gasoline, fuel gases, petrol, naphtha
Fermentation	Ethyl alcohol, acetic acid
Wood	Methyl alcohol, acetone

How carbon binds with itself?

Carbon is a major part of all living things. In the air, it is present as carbon dioxide and comprises around 0.03% of the total atmosphere.

Carbon exhibits two important properties − catenation & tetravalency.

Carbon can combine with other atoms of carbon to form long chains and rings. These chains and rings are not only long but also very stable. This is because carbon can form strong single, double, and triple bonds with other atoms of carbon.

Carbon is a non-metal having the symbol ‘C’ and atomic number six. Since the atomic number of carbon is six, its electronic configuration is 2, 4. This means that carbon contains two electrons in K-shell and 4 electrons in L-shell (outermost shell). Hence, it has four electrons in its valence shell.

Since carbon has four electrons in its valence shell, it requires four more electrons to complete its octet. Therefore, it is a tetravalent element.

In order to complete its octet i.e., to attain the noble gas configuration and to stabilise itself, carbon can:

• Either lose four electrons to form C⁴⁺ or gain four electrons to form C^4-. This, however, requires a lot of energy and would make the system unstable.
• Therefore, carbon completes its octet by sharing its four electrons with the other carbon atoms or with atoms of other elements.

The bonds that are formed by sharing electrons are known as covalent bonds. Covalently bonded molecules have strong intermolecular forces, but intramolecular forces are weak.

Carbon has four valence electrons and requires four more electrons to complete its octet. Therefore, it is capable of bonding with four other atoms of carbon or atoms of other elements having a valency of 1.

For example, the simplest molecule (methane) can be formed with hydrogen (H) atoms that have only one electron in their K-shell. To attain the noble gas configuration, carbon combines with four hydrogen atoms as shown in the figure.

Characteristics of organic compounds: Organic compounds show the following characteristics.

• They are compounds of carbon.
• They can exist in all three states i.e., solid, liquid, and gas.
• They are covalent compounds.
• They are soluble in organic solvents.
• They are poor conductors of electricity.
• They are volatile and flammable.

Classification of organic compounds: Organic compounds can be classified into the following categories:

On the basis of structure

• Open chain or aliphatic compounds.
• Closed chain or cyclic compounds.

On the basis of ring system

• Carbocyclic or homocyclic compounds have a ring comprising only of carbon atoms.
• Heterocyclic compounds contain other elements besides carbon in the ring.

 

 

At the beginning of the 19^th century, compounds obtained from plants and animals were regarded as organic compounds.

Organic compounds that contain both hydrogen and carbon are called hydrocarbons. These are parent fundamental compounds.

Classification of hydrocarbons

Hydrocarbons are classified on the basis of their structure and …