Maharashtra Board Class 11 Chemistry Chapter 14 Basic principles of Organic Chemistry PDF Download

14. Basic Principles Of Organic Chemistry

14.1 Introduction

Of all the elements, only carbon is able to form an immense array of compounds, ranging from methane having one carbon atom to deoxyribonucleic acid (DNA) with billions of carbon atoms. Crude oil is a complex mixture of compounds called hydrocarbons. The pharmaceutical industry is one of the most important chemical industries that provides us medicines which are organic compounds. We need to study the organic compounds for they are interesting in their own right and their functions are greatly important to life.

Which is the essential element in all organic compounds?

What is the unique property of carbon that makes organic chemistry a separate branch of chemistry?

Which classes of organic compounds are often used in our daily diet?

Find out the structures of glucose, vanillin, camphor and paracetamol using internet. Mark the carbon atoms present in them. Assign the hybridization state to each of the carbon and oxygen atom. Identify sigma (σ) and pi (π) bonds in these molecules.

14.2 Structural Representation Of Organic Molecules

In the previous standards you learnt how to write structural formulae and electron dot structure of hydrocarbons. Structural formula of a molecule shows all the constituent atoms denoted with their symbols and all covalent bonds therein represented by a dash joining mutually bonded atoms. For example, structural formula of CH₄ is:

In the electron dot structures of molecules, the valence electrons of all the atoms are shown as dots around them. Two dots drawn in between two atoms indicate one covalent bond between them. For example, the electron dot structure of methane is shown here.

Electron dot structures are called Lewis structures and the dash formula represents simplified Lewis formula. Chemists have developed some more ways to represent organic molecules fulfilling specific requirements.

14.2.1 Condensed Formula

The complete structural formula can be further simplified with hiding of some or all the covalent bonds and indicating the number of identical groups attached to an atom by a subscript. The resulting formula of a compound is known as condensed formula. For example: condensed formula of ethane can be written as CH₃ - CH₃ or CH₃CH₃.

14.2.2 Bond Line Formula Or Zig-Zag Formula

In this representation of a molecule symbols of carbon and hydrogen atoms are not written. The lines representing carbon-carbon bonds are drawn in a zig-zag manner and the terminals of the zig-zag line represent methyl groups. The intersection of lines denotes a carbon atom bonded to appropriate number of hydrogen which satisfy the tetravalency of carbon atoms. For example: propane is represented by the zig-zag formula. However the heteroatoms or hydrogen atoms bonded to heteroatoms are written clearly. For example: The bond line formula of C₂H₅OH is /OH.

Teacher's Note

Carbon atoms can form long chains and rings. Like beads on a thread, carbon atoms link together to make many different compounds. In India, crude oil from the ground has lots of these carbon compounds.

Exam Trick

Remember: Bond line = no carbon and hydrogen atoms written. Just lines and corners show carbons. Like a road map where corners are towns (carbons).

Points to Remember

Structural formula shows all atoms and all bonds.

Electron dot structures are also called Lewis structures.

Condensed formula hides some bonds but shows numbers.

Bond line formula uses only lines and corners for carbons.

Heteroatoms like O and N are always written clearly.

Draw the structural formula of ethane.

Draw electron-dot structure of propane.

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