Theory Of Structure Of Organic Molecules

Studies of organic chemistry must arrive at the molecular level, due to physical and chemical properties of compounds described in the structure and bonding of molecules. Four elements, hydrogen, carbon, oxygen, and nitrogen is a key element of organic compounds. Therefore, our understanding of organic chemistry must start from the electron structure and properties of these elements.

There are three theories to describe the structure of organic molecules :

1. Classical Molecular Structure Theory = Theory of Molecular Structure Kekulé

The molecular structure Kekulé valence based on the constituent atoms,so that atoms models made like the following:                H-           -O-           -N-          -Cl           -C-  

The letter describes the atom, line describing valence, also called the valence. Tsb structure formed by overlapping valence line, called the bond line. single bond occurs when two atoms are bonded by a bonding line, the double bond occurs when two atoms are bound by 2 line bond, triple bond occurs when two atoms are bound by the 3 line bond.

The theory also explains the classical structure of functional groups, is the position of chemical reactivity. Two or more substances that have similar chemical properties thought to have the same functional groups. The transformation of chemical substances in organic functional groups was only one transformation into functional groups other.

2. Lewis Structure Theory

The theory of the structure based on the theory of octets. Atom depends on the high reactivity of low energy electrons. Electrons in the outer shell of high-energy, so that these outer electrons that cause the binding nature of the atom. Outermost valence electrons = electrons.Lewis modify Borh atom model with the theory of Kekulé structures, namely: Atom expressed by letters, describing grain by electron-electron core. The electrons in the outer shell described as the points that surround the ears.Line Kekulé valence structure theory has the physical meaning of e-single. Kekulé theory is not aware of the concept of e-solitary pair.  

3. Linus Pauling's theory of structure

This theory is based on quantum mechanics. From this theory was born the concept of orbitals, namely the space around the core of the probability to find electrons.Electron kinetic energy they will depend on:n = principal quantum number, n = 1,2,3, ...l = azimuthal quantum number, m = 0,1, ... (n-1)m = magnetic quantum number, m = -1.0, +1  

Hybridization is a concept of atomic orbitals mix to form new hybrid orbitals suitable for the qualitative picture of atomic bonding properties. Hybrid orbitals are very useful in explaining the form of molecular orbital of a molecule.

Hybridization was not the atomic form (ground state): empty orbitals, one orbital filled, and filled two orbitals. Atoms form they will be unable to explain the structure of methane and the structure of the double bind, then the concept of atoms arranged terhibridisasi, namely:a.Konsep sp3 Hybridization   to explain the structure of a single bond to carbon.b.Konsep sp2 Hybridization   to explain the structure of the double bond at carbon.c. The concept of sp Hybridization   to explain the structure of the carbon triple bond.