🧪 NCERT Chemistry · Class 11 · Chapter 8
Organic Chemistry: Some Basic Principles and Techniques
UNIT 8
ORGANIC CHEMISTRY – SOME BASIC PRINCIPLES AND TECHNIQUES
Objectives
After studying this unit, you will be able to
In the previous unit you have learnt that the element carbon has the unique property called catenation due to which it forms covalent bonds with other carbon atoms. It also forms covalent bonds with atoms of other elements like hydrogen, oxygen, nitrogen, sulphur, phosphorus and halogens. The resulting compounds are studied under a separate branch of chemistry called organic chemistry. This unit incorporates some basic principles and techniques of analysis required for understanding the formation and properties of organic compounds.
8.1 GENERAL INTRODUCTION
Organic compounds are vital for sustaining life on earth and include complex molecules like genetic information bearing deoxyribonucleic acid (DNA) and proteins that constitute essential compounds of our blood, muscles and skin. Organic compounds appear in materials like clothing, fuels, polymers, dyes and medicines. These are some of the important areas of application of these compounds.
Science of organic chemistry is about two hundred years old. Around the year 1780, chemists began to distinguish between organic compounds obtained from plants and animals and inorganic compounds prepared from mineral sources. Berzilius, a Swedish chemist 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 a laboratory.
The development of electronic theory of covalent bonding ushered organic chemistry into its modern shape.
8.2 TETRAVALENCE OF CARBON: SHAPES OF ORGANIC COMPOUNDS
8.2.1 The Shapes of Carbon Compounds
The knowledge of fundamental concepts of molecular structure helps in understanding and predicting the properties of organic compounds. You have already learnt theories of valency and molecular structure in Unit 4. Also, you already know that tetravalence of carbon and the formation of covalent bonds by it are explained in terms of its electronic configuration and the hybridisation of and orbitals. It may be recalled that formation and the shapes of molecules like methane , ethene , ethyne are explained in terms of the use of , and hybrid orbitals by carbon atoms in the respective molecules.
Hybridisation influences the bond length and bond enthalpy (strength) in compounds. The hybrid orbital contains more character and hence it is closer to its nucleus and forms shorter and stronger bonds than the hybrid orbital. The hybrid orbital is intermediate in character between and and, hence, the length and enthalpy of the bonds it forms, are also intermediate between them. The change in hybridisation affects the electronegativity of carbon. The greater the character of the hybrid orbitals, the greater is the electronegativity. Thus, a carbon atom having an hybrid orbital with 50% character is more electronegative than that possessing or hybridised orbitals. This relative electronegativity is reflected in several physical and chemical properties of the molecules concerned, about which you will learn in later units.
Open the app to read all 19 Chemistry chapters free
You're reading a free preview of Organic Chemistry: Some Basic Principles and Techniques. Get every PYQ-marked NCERT line, all chapters, in the MedicNEET app — free.
Open in the MedicNEET app