Basic Concepts Of Organic Chemistry - Introduction

BASIC CONCEPTS OF ORGANIC CHEMISTRY

Introduction

Initially (before 1828), the name organic chemistry was given for the chemistry of compounds obtained from plants and animals (i.e, from living organisms). The word organic signifies life. Lavoisier (who is considered as the father of chemistry) showed that the compounds obtained from plants are often made of C, H and O and the compounds obtained from animals contain C, H, O, N, S, P. ..... etc.

Berzelius proposed vital force theory (a theory of life process) to deal with organic compounds. The vital force theory suffered blow in 1828 when Wohler synthesized the first organic compound urea in the laboratory from an inorganic compound, i.e, from ammonium cyanate (NH4 CNO).

2KCNO + (NH4)2SO4 --- ∆ ---  >2NH4CNO+K2SO4

or Pb(CNO)2 + 2NH4OH  -- ∆ --- > 2NH4CNO + Pb(OH)2

NH ₄ CNO       -- ∆ --- >  NH ₂ CONH ₂

Rearrangement

Later on, a further blow to vital force theory was given by Kolbe (1845) who prepared acetic acid, the first organic compound, in laboratory from its elements.

Now a days organic chemistry is defined as the chemistry of carbon compounds or the chemistry of hydrocarbons and their derivatives. Organic compounds obey the same fundamental laws of chemistry as the inorganic compounds. However they are studied as a separate branch of chemistry because of two reasons:

1.     The total number of organic compounds known so far exceeds several times the total number of inorganic compounds known.

2.     There are marked differences between the structure, composition and behaviour of organic and inorganic compounds. The phenomenon of isomerism and tendency of catenation are unique properties of organic compounds.

Catenation

1.    The tendency of atoms of an element to unite with each other forming a chain of covalent bond is known as catenation.

2.    Catenation may give rise to open chain or closed chain compounds.

3.    Carbon possesses maximum tendency for catenation i.e. Bond energy (kcal mol^-1) for catenation of C is maximum.

C-C,  Si-Si,  N-N,   P-P,          O-O,  S-S

85      54      39      50      35      54

4.    Carbon also forms double as well as triple bonds.

5.    A large number of compounds of carbon are known due to catenation.

6.    The  stability  or  strength  of  bond  decreases  as  the  bond  energy

Decreases.

Hence    the     catenation    order          among         the     following    is C > Si » S>P>N>O.