NEET Chemistry Notes Some Basic Principles and Techniques – Concept of Organic Chemistry
Concept of Organic Chemistry
Concept of Organic Chemistry
The hydrides of carbon (hydrocarbons) and their derivatives are called organic compounds. The branch of chemistry which deals with these compounds is called organic chemistry.
Bonding in Organic Compounds
Carbon is the essential element of all organic molecules and its electronic configuration is 2,4. Hence, it is not possible for carbon to accept or donate 4 electrons to achieve inert gas configuration (to achieve stability), due to energy conceptions. Thus, carbon always forms covalent bonds.
The tetravalency of carbon can be explained by the excited state concept, i.e. by moving one of the paired 2s electron to empty 2p orbital by gaining energy from the system (according to classical concept of bonding) however 4 equivalent C—H bonds in CH4 is explained on the basis of concept of hybridisation (according to modern concept of bonding). Carbon has a unique property that it can form both a and
Hybridisation and Shape
Hybridisation is the intermixing of orbitals of almost similar energy to form the same number of orbitals of exactly similar energy.
The carbon atom shows three types of hybridisations depending upon the number of formed in its compounds. If there are four , the hybridisation is sp2 with tetrahedral shape, if three , the hybridisation is sp2 with trigonal planar shape and if only two , the hybridisation is sp with linear shape.
Usually saturated hydrocarbons are sp3 hybridised while unsaturated hydrocarbons may be sp2 or sp hybridised.
An atom or group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds e.g. carboxylic acid group (—COOH), aldehydic group (— CHO), etc.
A homologous series can be defined as a group of compounds in which the members have similar structural features and similar chemical properties and the successive members differ in their molecular formula by —CH2 group.
Characteristics of Homologous Series
The general characteristics of a homologous series are:
- All compounds in the series can be represented by one general formula.
- The molecular mass of every two adjacent members differ by 14 (CH2 =12 + 2×1=14).
- All compounds in the series have similar chemical properties because of the presence of same functional group.
- The members of the series show a gradual gradation in their physical properties like solubility, density, melting and boiling points. The physical properties generally increase as the molecular mass increases.
Classification of Organic Compounds
The organic compounds have been classified on the basis of carbon skeleton (structure) or functional groups or the concept of homology, i.e. the series in which two successive members differ by a—CH2 unit or 14 unit mass.
Classification Based on Structure
On this basis the organic compounds are classified as:
Classification Based on Functional Groups
The compounds of only carbon and hydrogen are called hydrocarbons. All other compounds are obtained from hydrocarbons by the replacement of one or more hydrogen atoms with other atoms or groups. Various classes of compounds having some of the common functional groups are listed in the following table.