28-02-2013, 12:24 PM
MOLECULAR ORBITAL THEORY OF ETHYLENE AND POLYENES
[attachment=52178]
FEATURES OF M.O.T
1.THE NUMBER OF MOLECULAR ORBITAL PRODUCED IS EQUAL TO THE NUMBER OF COMBINING ATOMIC ORBITAL
2.EACH MOLECULE ORBITAL IS DISCRIBE BY Ψ WAVE FUNCTION WHICH IS CALLED AS MOLECULAR ORBITAL OF WAVE FUNCTION
3.EACH IS ASSOCIATED WITH A DEFINITE ENERGY VALUE & TOTAL VALUE OF THE MOLECULE IS THE SUM OF THE ENERGY OF THE OCCUPIED MOLECULAR ORBITAL
4.RULES OF MOLECULAR ORBITAL
PAULI’S EXCLUSION-NO 2 ELECTRONS IN AN ATOM HAVE SAME QUANTUM NUMBER
HUND’S RULE FOR MAXIMUM MULTIPLICITY-THOSE ORBITAL HAVING SAME ENERGY LEVEL SHOULD HAVE 1 ELECTRON EACH BEFORE PAIRING
INTRODUCTION OF ETHYLENE MOLECULE
TWO CARBON sp2 ORBITALS COMBINE WITH ONE HYDROGEN 1S ORBITAL EACH TO FORM C H BONDS sp2 - 1S σ BONDS
THE REMAINING CARBON SP2 BONDING ORBITAL FROM EACH CARBON IS USED TO FROM C C BOND
IN ETHYLENE sp2 - sp2 BOND
1 HALF OCCUPIED, UNHYBRIDIZED 2Pz ORBITAL LEFT OVER ON EACH CARBON COMBINE TO FORM 2 NEW P-ORBITAL
EACH CARBON ATOM CONTRIBUTES 1 ELECTRON TO OCCUPY THE BONDING ORBITAL TO FORM A PI(π) BOND
ATOMIC ORBITAL AND MOLECULAR ORBITAL OF 1,3-BUTADIENE
THE ABOVE DIAGRAM SHOWS THE RELATIVE ENERGIES OF THE π MOLECULAR ORBITALS OF 1,3-BUTADIENE (DERIVED FROM ETHENE) AND THE ELECTRON CONFIGURATION.
THE HORIZONTAL CENTER LINE DENOTES THE ENERGY OF A
ATOMIC ‘ P’ ORBITAL. ORBITALS BELOW THAT LINE ARE BONDING THOSE ABOVE ARE ANTI-BONDING.
WE NOW HAVE 4 ELECTRONS TO ARRANGE, 1 FROM EACH OF THE ORIGINAL ATOMIC ‘P’ ORBITALS. THESE ARE ALL PAIRED IN THE TWO STABILISED PI BONDING ORBITALS, Π1 AND Π2. THE HIGHEST OCCUPIED MOLECULAR ORBITAL OR HOMO IS Π2 IN 1,3-BUTADIENE (OR ANY SIMPLE CONJUGATED DIENE).
IN CONTRAST, THE ANTI-BONDING Π* ORBITALS CONTAIN NO ELECTRONS. THE LOWEST UNOCCUPIED ORBITAL OR LUMO IS Π3 IN 1,3-BUTADIENE (OR ANY SIMPLE CONJUGATED DIENE).
EXTENTION OF ETHYLENE
The interaction of atomic orbital giving rise to molecular orbital is the simplest type of conjugation. Thus in ethylene the two P orbital can be describe as being conjugated with each other to make the π bond. The simplest extension to make longer conjugated system is to add one p orbital at a time to the π bond to make successively π components of the allyl system with three carbon atoms, of butadiene with four of the pentadienyl system with five and so on. Huckel Theory applies because, in each case we separate completely π system from a frame work and we can continue to use the electron in the box model.
[attachment=52178]
FEATURES OF M.O.T
1.THE NUMBER OF MOLECULAR ORBITAL PRODUCED IS EQUAL TO THE NUMBER OF COMBINING ATOMIC ORBITAL
2.EACH MOLECULE ORBITAL IS DISCRIBE BY Ψ WAVE FUNCTION WHICH IS CALLED AS MOLECULAR ORBITAL OF WAVE FUNCTION
3.EACH IS ASSOCIATED WITH A DEFINITE ENERGY VALUE & TOTAL VALUE OF THE MOLECULE IS THE SUM OF THE ENERGY OF THE OCCUPIED MOLECULAR ORBITAL
4.RULES OF MOLECULAR ORBITAL
PAULI’S EXCLUSION-NO 2 ELECTRONS IN AN ATOM HAVE SAME QUANTUM NUMBER
HUND’S RULE FOR MAXIMUM MULTIPLICITY-THOSE ORBITAL HAVING SAME ENERGY LEVEL SHOULD HAVE 1 ELECTRON EACH BEFORE PAIRING
INTRODUCTION OF ETHYLENE MOLECULE
TWO CARBON sp2 ORBITALS COMBINE WITH ONE HYDROGEN 1S ORBITAL EACH TO FORM C H BONDS sp2 - 1S σ BONDS
THE REMAINING CARBON SP2 BONDING ORBITAL FROM EACH CARBON IS USED TO FROM C C BOND
IN ETHYLENE sp2 - sp2 BOND
1 HALF OCCUPIED, UNHYBRIDIZED 2Pz ORBITAL LEFT OVER ON EACH CARBON COMBINE TO FORM 2 NEW P-ORBITAL
EACH CARBON ATOM CONTRIBUTES 1 ELECTRON TO OCCUPY THE BONDING ORBITAL TO FORM A PI(π) BOND
ATOMIC ORBITAL AND MOLECULAR ORBITAL OF 1,3-BUTADIENE
THE ABOVE DIAGRAM SHOWS THE RELATIVE ENERGIES OF THE π MOLECULAR ORBITALS OF 1,3-BUTADIENE (DERIVED FROM ETHENE) AND THE ELECTRON CONFIGURATION.
THE HORIZONTAL CENTER LINE DENOTES THE ENERGY OF A
ATOMIC ‘ P’ ORBITAL. ORBITALS BELOW THAT LINE ARE BONDING THOSE ABOVE ARE ANTI-BONDING.
WE NOW HAVE 4 ELECTRONS TO ARRANGE, 1 FROM EACH OF THE ORIGINAL ATOMIC ‘P’ ORBITALS. THESE ARE ALL PAIRED IN THE TWO STABILISED PI BONDING ORBITALS, Π1 AND Π2. THE HIGHEST OCCUPIED MOLECULAR ORBITAL OR HOMO IS Π2 IN 1,3-BUTADIENE (OR ANY SIMPLE CONJUGATED DIENE).
IN CONTRAST, THE ANTI-BONDING Π* ORBITALS CONTAIN NO ELECTRONS. THE LOWEST UNOCCUPIED ORBITAL OR LUMO IS Π3 IN 1,3-BUTADIENE (OR ANY SIMPLE CONJUGATED DIENE).
EXTENTION OF ETHYLENE
The interaction of atomic orbital giving rise to molecular orbital is the simplest type of conjugation. Thus in ethylene the two P orbital can be describe as being conjugated with each other to make the π bond. The simplest extension to make longer conjugated system is to add one p orbital at a time to the π bond to make successively π components of the allyl system with three carbon atoms, of butadiene with four of the pentadienyl system with five and so on. Huckel Theory applies because, in each case we separate completely π system from a frame work and we can continue to use the electron in the box model.