Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon-
containing compounds, which include not only hydrocarbons but also compounds with any number of other
elements, including hydrogen, nitrogen, oxygen, halogens, phosphorus, silicon, and sulphur.
This branch of chemistry primarily deals with the structure and chemical composition of organic compounds, the
physical and chemical properties of organic compounds, and the chemical reactions undergone by these
compounds. Advancements in the field of organic chemistry have made numerous contributions to human
society, such as the synthesis of several drugs, polymers, and other natural products. Synthetic organic chemistry
is an important application of organic chemistry that deals with the design and construction of organic
compounds for practical purposes.
The range of application of organic compounds is enormous and also includes, but is not limited to,
pharmaceuticals, petrochemicals, food, explosives, paints, and cosmetics.
Carbon is unique in its chemical properties because it forms a number of components superior than the
total addition of all the other elements in combination with each other.
Due to the specific properties of the element, Carbon has established its importance among the other
elements. The properties which make carbon so important are:
Size of a carbon atom
Although there is no specific definition, the compounds in solid, liquid or gaseous state which contain
covalently bonded carbon atoms in their molecules are known as organic compounds.
5. Hybridization of Carbon
Hybridization is the concept of combining atomic orbitals to make new hybrid orbitals appropriate to
represent their properties of bonding. Hybridized orbitals are helpful in describing the shape of molecular
orbitals apart from being a major part of valence bond theory.
The name hybrid applies to the atomic orbitals that contribute to the hybridization. For example, in
methane whose chemical formula is CH4, a set of sp3 orbitals develops by combining one s-orbital and
three p-orbitals on the carbon atom. These orbitals direct towards the four hydrogen atoms placed at the
vertices of a regular tetrahedron.
Ethene (C2H4) consists of a double bond between the carbon atoms. Here, the carbon hybridizes by sp2.
In sp2 hybridization, the 2s orbital mingles with two among the three 2p orbitals available, making total
3sp2 orbitals with one remaining p-orbital.
6. In ethane, two atoms of carbon develop a sigma bond by overlaying two sp2 orbitals, where every carbon
atom makes two covalent bonds with hydrogen by overlapping all s-sp2 with 120◦ angles. The pi bond
among the carbon atoms develops by a 2p-2p overlap. The hydrogen-carbon bonds have equal length and
strength that satisfies with experimental proof.
Many bonds also exist between non-similar atoms. When two atoms of oxygen are brought near opposite
sides of the carbon atom in CO2, one among the p orbitals on every oxygen makes a pi bond with anyone
among the p-orbitals of carbon. Here, the sp hybridization forms two double bonds.
Hybridization of Carbon
7. Tetravalency of carbon
1. Catenation – Catenation can be defined as the self-linking of atoms of an element to form chains and
rings. This definition can be extended to include the formation of layers (two-dimensional catenation)
and space lattices (three-dimensional catenation).
2. Tetravalency and small size – Carbon exhibits’ tetravalency. The tetravalency of carbon can be satisfied
by forming bonds with carbon, hydrogen or other atoms. The carbon atom has 4 electrons in its valence
shell. In order to account tetravalency it is believed during the process of bond formation which is energy-
releasing process the two electrons in the 2s orbital get unpaired and out of them, one is promoted to
8. Ground state electronic configuration of carbon is 1s2, 2s2, 2p2. It has 4 valence electrons, so the
probability of formation of four bonds is maximum. The bonds formed by the s orbital electrons
will not be the same as that of p orbital electrons. So in the formation of one molecule of CH4,
there will be a combination of 1 C atom with 4 H atoms.
The following types of bonds can be formed: C(s)-H(s), C(s)-H(s), C (p)-H(s) and C (p)-H(s). Out of
the four bonds, we have two ‘directional’ C (p)-H(s) and two non-directional bond C(s)-H(s). (Note:
As we know that s orbitals are spherical and do not have any specific direction and p orbitals have
shapes in three directions x, y, and z-axis.) The strength of the bond will also differ as C (p)-H(s)
bond will be less strong than the C(s)-H(s) bond as s overlapping is stronger
But practically all the bonds of CH4 are identical. This creates a problem. To solve this problem,
hybridization theory has been stated. It is mainly a concept in which atomic orbitals are mixed
with new hybrid orbitals which are most suited for the pairing of electrons to form chemical
bonds. It can be understood by the fig given below:
9. In the fig, three p and one s-orbital are hybridized to give four
identical sp3 hybridized orbitals.
Similarly, we can also get sp and sp2 hybridization.
The only change will be that sp2 will have only two p orbitals.
Now from the VSEPR theory, we know that sp and sp2
hybridized molecules are planar in structure.
Whereas sp3 hybridized molecules take tetrahedral shape to
become more stable (this structure leads to minimum energy
10. Structural Representation of Organic Compounds:
Though an organic compound has only one chemical formula, structurally it can be depicted in numerous
ways. The three structural formulas – complete structure, condensed structure, and bond line structural
formulas are explained below.
Complete Structural Formula:
The Lewis dot structure is considered as the complete structural formula. In Lewis structure, the covalent
bonds in the compound are denoted by a dash (―). This helps to emphasize the number of bonds
formed by the electrons. Every single bond, a double bond, and a triple bond are represented by one
dash, double dash, and triple dash respectively. It illustrates every single bond formed between every
atom in the compound, thus called complete structural formula.
11. Condensed Structural Formula:
Since complete structural formula consumes much time and space to represent the structure, we can
condense them. This is the condensed structural formula, where replacing some dashes/bonds by a
number of identical groups attached to an atom by a subscript.
Bond Line Structural Formula:
A bond lines structural formula is another way of structural representation of organic compounds. Here, every
bond is represented as a line in a zigzag manner. If not specified, every terminal is assumed to be a methyl (-
12. 3-D Representation of Organic Compounds:
The organic compounds which were represented using structural formulas in the previous section are three-
dimensional compounds. In order to draw the 3-D structure of an organic compound, we can use wedge-
The bond that protrudes out of the plane of paper towards the viewer is denoted by a solid wedge while
that project away from the viewer or into the plane of the paper is denoted by a dashed wedge and the
bond in the plane of the paper is represented by a line.
13. 1.Acyclic or Open Chain Compounds & Alicyclic or Closed Chain or Ring Compounds – Organic compounds
are classified as open-chain compounds and closed chain compounds in terms of the carbon chain. Also
termed as Organic Compounds Acyclic or Open Chain or Aliphatic Compounds Cyclic or Closed Chain or
Ring Compounds Alkanes Alkenes Alkynes
2.Aromatic Compounds – Plants and micro-organisms have an exclusive route to benzene-ring
compounds. The great majority of aromatic compounds in nature, therefore, are produced by plants and
microorganisms, and animals are dependent upon plants for many aromatic compounds either directly
3.Heterocyclic Aromatic Compounds – In the twentieth century it is witnessed that the first inorganic
heteroaromatic compound produced in the laboratory. Some of these heterocyclic aromatic compounds
are very important in biochemical processes, drugs, and agrochemicals.
Classification of Organic Compounds
15. Nomenclature of Organic Compounds - IUPAC
What is IUPAC Nomenclature?
IUPAC nomenclature of organic compounds refers to the systematic approach taken for the nomenclature of
organic compounds as per the recommendation of the International Union of Pure and Applied Chemistry
(often abbreviated to IUPAC).
A set of rules formulated by IUPAC (the International Union of Pure and Applied Chemistry) for systematic
nomenclature of organic compounds which is revised from time to time. The IUPAC nomenclature of organic
compounds essentially consists of three parts which are stem name, prefix and suffix.
It is interesting to note that the existence of preferred IUPAC names does not prevent the use of other names
to take into account a specific context or to emphasize structural features common to a series of compounds.
Preferred IUPAC names belong to a “preferred IUPAC nomenclature”. Any name other than a preferred IUPAC
name (as long as it is unambiguous and follows the principles of the IUPAC recommendations herein) is
acceptable as a general IUPAC name in the context of a “general IUPAC nomenclature”.
16. According to the Guidelines set by IUPAC, the nomenclature of compounds must follow these steps:
1.The Longest Chain Rule: The parent hydrocarbon must be identified and subsequently named. The parent chain
belonging to the compound in question is generally the longest chain of carbon atoms, be it in the form of a straight
chain or a chain of any other shape.
2.The Lowest Set of Locants: The carbon atoms belonging to the parent hydrocarbon chain must be numbered using
natural numbers and beginning from the end in which the lowest number is assigned to the carbon atom which carries
3.Multiple instances of the same substituent: Prefixes which indicate the total number of the same substituent in the
given organic compounds are given, such as di, tri, etc.
4.Naming of different substituents: In the organic compounds containing multiple substituents, the corresponding
substituents are arranged in alphabetical order of names in the IUPAC nomenclature of organic compounds in question.
5.The naming of different substituents present at the same positions: In the scenario wherein two differing substituent
groups are present at the same position of the organic compound, the substituents are named in ascending alphabetical
6.Naming Complex Substituents: Complex substituents of organic compounds having branched structures must be
named as substituted alkyl groups whereas the carbon which is attached to the substituent group is numbered as one.
These branched and complex substituents must be written in brackets in the IUPAC nomenclature of the corresponding
Nomenclature of Organic Compounds - IUPAC
17. Nomenclature of Organic Compounds - IUPAC
The IUPAC nomenclature of alkanes, alkenes, and alkynes are discussed in the subsections below.
The General formula of alkanes corresponds to CnH2n+2
The suffix ‘ane’ is generally used to describe alkanes. Examples for the nomenclature of alkanes as per IUPAC
guidelines include methane for the compound CH4 and Butane for the compound C4H10
The General formula of alkenes is described as CnH2n
The suffix ‘ene’ is used to describe alkenes via IUPAC norms. Examples for the nomenclature of alkenes
include the name ethene used to describe the compound given by C2H4 and Propene used to describe the
compound given by C3H6
The General formula of alkynes is CnH2n-2
The suffix ‘yne’ is generally used to describe alkynes. An example of the IUPAC nomenclature of alkynes is:
ethyne used to describe the compound given by C2H2
18. Nomenclature of Organic Compounds - IUPAC
Example of IUPAC Nomenclature
Considering the following Example:
•There exist 9 carbon atoms on the straight chain and the 5th carbon atom (from both ends of the chain)
consists of a substituent group which in turn has 3 carbon atoms in a chain.
•Furthermore, there the first and second carbons of this substituent chain have an additional CH group
attached to them.
•In the nomenclature of this compound, the 9 membered carbon chain is identified as the parent chain and is
•The substituent chain attached to position 5 of the parent chain is 3 members long, with 2 methyl groups
attached at positions 1 and 2.
•Thus the carbon chain substituent group on the parent chain can be called 1,2 dimethyl propane. The name
for the substituent chain containing this compound would be 1,2 dimethyl propyl.
•Substituting this name on the parent chain, the IUPAC name of the compound in question is found to be: 5-
(1,2 dimethyl propyl) nonane.
19. 1. Fundamental Concepts
- Tetravalence of carbon;
- Carbon Chain linear cyclic;
- Concept of isometry;
2. General concepts on
- The saturated hydrocarbons: methane;
- Unsaturated hydrocarbons: ethylene, acetylene;
- The aromatic hydrocarbons: chloroform;
- The halogen derivatives of hydrocarbons
- The alcohols methanol, ethanol;
- The PWnols;
- The aldehydes: formaldehyde;
- The ketones: acetone;
- The organic acids: acetic acids;
- The amines, methylamine;
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- The acids: aniline