Introduction to Organic Compounds: Organic compounds are the specific compounds associated with life processes. The constituting elements of these compounds are carbon and hydrogen. From sugar to starch, from bread to eggs-almost all of the foodstuffs that we consume every day are made of organic compounds. These compounds derived mainly from plants and animals have been known to man since prehistoric times. The term “organic compound” was coined by Berzelius in \(1807.\)

General Introduction to Organic Compounds

Hydrocarbons-as the name suggests, are compounds composed of carbon and hydrogen atoms only. The element carbon exclusively forms these compounds. Carbon exhibits a chemical diversity unrivalled by any other chemical element. The versatile nature of carbon is because of its:

1. Atomic size
2. Tetravalent nature
3. High catenating (self-linking) ability to form long chains.

The branch of science that deals with the scientific study of structure, properties and reactions of hydrocarbons and their derivatives are known as organic chemistry.

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Bonding in Organic Compounds

The bonding that exists between carbon and hydrogen is covalent. A covalent bond is a type of chemical bond in which each of the participating atoms shares their electron pairs. Due to the presence of a covalent bond, the organic compounds exhibit specific characteristics. These include:

1. Low boiling and melting points compared to the inorganic compounds.
2. The phenomenon of isomerism in which compounds with single molecular formula represents several organic compounds differing in physical and chemical properties.

Classification of Organic Compounds

Based on the arrangement of carbon atoms, organic compounds are broadly categorised as-

Saturated hydrocarbons have only single bonds that can appear as a straight chain or can have branches). These hydrocarbons are commonly known as alkanes. Each alkane has a systematic name that depends on the number of carbon atoms in the molecule. 

The most frequently used nomenclature worldwide is the one created and developed by the International Union of Pure and Applied Chemistry (IUPAC). The basename or the parent name of an organic compound depends on the total number of carbon atoms. This is shown as below-

Stem	Number of C’s in the parent chain
Meth-	\(1\)
Eth-	\(2\)
Prop-	\(3\)
But-	\(4\)
Pent-	\(5\)
Hex-	\(6\)
Hept-	\(7\)
Oct-	\(8\)
Non-	\(9\)
Dec-	\(10\)

Alkanes consist of a stem plus the ending –ane. 

Stem-	Number of carbon atoms	Name
Meth	\(1\)	Methane
Eth	\(2\)	Ethane
Prop	\(3\)	Propane

The formulae and molecular models of the three simplest alkanes are shown below-

Unsaturated hydrocarbons have either double \(({\rm{C = C}})\) or triple bonds \(({\rm{C}} \equiv {\rm{C)}}\) These hydrocarbons are commonly known as alkenes and alkynes, respectively. Each alkene and alkynes have a systematic name that also depends on the number of carbon atoms in the molecule. Alkenes consist of a stem plus the ending\( – {\rm{ene}}\) and alkynes consist of a stem plus the ending \( – {\rm{yne}}\)

Stem –	Number of carbon atoms	Alkenes	Alkynes
Eth	\(2\)	Ethene	Ethene
Prop	\(3\)	Propyne	Propyne

The formulae and molecular models of the two simplest alkenes are given below:

Ethene is also known as ethylene, while propene is commonly called propylene.

The formulae and molecular models of the two simplest alkynes: 

Ethyne is more commonly called acetylene.

Closed chain or cyclic hydrocarbons are formed when both the ends of an aliphatic carbon chain meet, a closed chain is obtained. When only one ring is present in the molecule, it is known as monocyclic, whereas the compounds with more than one ring of atoms are termed polycyclic.

Alicyclic closed ring organic compounds are ring derivatives of aliphatic hydrocarbons. These compounds contain at least three carbon atoms as three carbon atoms are required to form a ring. For example- Cyclobutane, Tetrahydrofuran

Homocyclic closed chain compounds consists of only one type of atom in the ring. For example- 

Heterocyclic closed chain compounds consists of heteroatoms such as \({\rm{O,N}}\) etc., in the carbon ring. For example –

Aromatic closed ring organic compounds – The cyclic unsaturated compounds that exhibit aromaticity are called aromatic compounds and are further classified into the following-

1. Benzenoid aromatic compounds are aromatic compounds that contain at least one benzene ring in their structure. 

For example –

2. Non-benzenoid aromatic compounds are highly unsaturated aromatic compounds that do not contain any benzene ring in their ring structure. These compounds have conjugated systems with a planar cyclic structure. For example

Functional Groups

When one of the \( – {\rm{H}}\) atoms in methane is replaced by some other group such as the \( – {\rm{OH}}\) group, then methane is converted into methanol, a type of alcohol with the formula \({\rm{C}}{{\rm{H}}_3}{\rm{OH}}\). Methanol is an organic compound that belongs to a new class of organic compounds known as alcohols.  Hence, a functional group is an atom or a group of atoms responsible for organic compounds’ characteristic chemical properties. These groups are also the site of chemical reactions in organic compounds. 

Organic compounds can be classified based on functional groups, which is as given below-

Isomerism

It is the phenomenon in which two or more compounds that possess the same molecular formula exhibit different chemical properties. Such compounds are called isomers. The following flow chart shows different types of isomerism.

In structural isomerism, compounds have the same molecular formula but differ in the spatial arrangement of the individual atoms. Structural isomerism is further classified into:

(i) Chain isomerism: When two or more compounds have the same molecular formula but differ in the arrangement of carbon skeletons, exhibit chain isomerism. For example,\({{\rm{C}}_5}{{\rm{H}}_{12}}\)

(ii) Position isomerism: Two or more compounds exhibit position isomerism when they have the same molecular formula but differ in the position of substituent atom or functional group on the carbon skeleton. For example, the molecular formula \({{\rm{C}}_3}{{\rm{H}}_8}{\rm{O}}\) represents two alcohols:

(iii) Functional group isomerism: Two or more compounds exhibit functional group isomerism when they have the same molecular formula but different functional groups. For example, the molecular formula \({{\rm{C}}_3}{{\rm{H}}_6}{\rm{O}}\) represents an aldehyde and a ketone:

(iv) Metamerism: Two or more compounds exhibit metamerism with the same molecular formula but differ in the alkyl chains on either side of the functional group. For example, \({{\rm{C}}_4}{{\rm{H}}_{10}}{\rm{O}}\) represents methoxypropane \(({\rm{C}}{{\rm{H}}_3}{\rm{O}}{{\rm{C}}_3}{{\rm{H}}_7})\) and ethoxyethane \(({{\rm{C}}_2}{{\rm{H}}_5}{\rm{O}}{{\rm{C}}_2}{{\rm{H}}_5})\).

Stereoisomerism

Stereoisomerism, also known as spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of covalent bonds but differ in the three-dimensional orientation of atoms or groups in space. This isomerism is further classified as geometrical and optical isomerism.

Representation of Organic Compounds

The molecular formula of an organic compound can be represented in a number of ways which are as follows–

Complete Structural Formula– Every single bond, a double bond, and a triple bond in the organic compound is represented by a single dash, double dash, and triple dash, respectively. A complete structural formula illustrates every single bond formed between every atom in the organic compound. For example –

Condensed Structural Formula– The dashes/bonds present in the complete structural formula are removed. The identical atoms or groups are represented by a numerical value equal to its count and written subscript to that particular atom or group. However, every carbon atom is represented individually. For example –

Bond Line Structural Formulas– In bond line notation, a zig-zag line represents every bond in the molecule. Every terminal in bond line notation is assumed to be a methyl \(( – {\rm{C}}{{\rm{H}}_3})\) group and the ends and vertices represent the carbon atoms. However, only the bonds between the carbon atoms are shown as lines. The atoms other than carbon and hydrogen are shown.

Three dimensional \((3{\rm{D}})\) representation– It is the wedge-dash method of representation of organic compounds. A solid wedge represents the bond that protrudes out of the plane of paper towards the viewer. A dashed wedge is used to represent the bond that projects away from the viewer or into the plane of the paper, and the bond that lies in the plane of the paper is represented by a line. 

Homologous Series

It is a series of organic compounds in which members of the series are denoted by a single general formula and differ from each other by a \( – {\rm{C}}{{\rm{H}}_2}\)  group. The individual members of a homologous series are called homologues. A \( – {\rm{C}}{{\rm{H}}_2}\) the group gets added to the chain while transforming a compound into its next homologue.

Due to structural similarity, the physical properties of a homologous series change regularly with the increasing number of carbon atoms. The members of a homologous series exhibit similar chemical properties because they have the same functional group.

Characteristics of Organic Compounds

Some of the general characteristics of organic compounds are:

1. Organic compounds comprise almost \(90\% \) of all known compounds and can be isolated as well as prepared in the laboratory.
2. The functional groups govern the properties of these compounds.
3. These are mostly insoluble in water but soluble in organic solvents.
4. They are combustible in nature.

Importance of Organic Compounds

1. The basic structures of life are made up of organic compounds.
2. Organic compounds are the primary components of many of the cycles that drive the earth, such as the oxygen and carbon cycle that includes the exchange of carbon between plants and animals in photosynthesis and cellular respiration.
3. Organic compounds combine with metals to form organometallic compounds. These compounds are important industrially. They are used as catalysts, promoters, analysers as well as stabilisers.

Summary

Organic compounds comprise a wide range of compounds with carbon and hydrogen as the basic elements. These compounds include complex molecules like deoxyribonucleic acid (DNA) and proteins that constitute essential compounds in our body. Hence, they are vital for sustaining life on earth. These chemicals appear in materials like polymers, fuels, clothing, dyes and medicines too. Petroleum and natural gas, which are the main components of fossil fuels, are also organic compounds. To have a detailed knowledge of these compounds, it is essential to classify them in a systematic manner. In this article, we discussed what organic compounds are, their basic characteristics and their importance. It also explains homologous series and their role in identifying organic compounds.

FAQs

Q.1. What is meant by organic compound?
Ans: The organic compound is a large class of chemical compounds in which one or more carbon atoms are covalently bonded to atoms of other elements, such as hydrogen, oxygen, or nitrogen. However, carbon compounds such as carbides, carbonates, and cyanides are not considered organic compounds.

Q.2. Why are organic compounds called organic?
Ans: Organic compounds are named so because these are carbon-containing compounds, and carbon compounds are mostly associated with living organisms. 

Q.3. What is the importance of organic chemistry in our daily lives?
Ans: Organic chemistry is important because they serve as the basis for all carbon-based on earth, create energy production in biological life, cause atmospheric depletion and release hydrocarbon energy.

Q.4. What are the types of organic compounds?
Ans: The four main types of organic compounds found in all living things include carbohydrates, proteins, lipids, and nucleic acids.

Q.5. What is the most important organic compound?
Ans: The most abundant organic compound is a carbohydrate, one of the four so-called molecules of life along with proteins, lipids and nucleic acids.

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