DELOCALISED MODEL OF BENZENE

Question 1

define addition reaction and substitution reaction

Answer 1

1-reaction in which a reactant is added to an unsaturated molecule to form a saturated molecule
2-reaction in which an atom or group of atoms is replaced by another atom or group of atoms

Question 2

define the term delocalised

Answer 2

sharing of electrons between more than 2 atoms and not localised to one atom

Question 3

Describe the features of the delocalised model

Answer 3

1-Benzene is a cyclic hydrocarbon with 6 carbon atoms and 6 hydrogen atoms
2-Six carbon atoms are arrange to form a planar hexagonal ring
3-each carbon atom is bonded to two other carbon atoms and hydrogen atom
4-shape around carbon atom is trigonal planar with a bond angle of 120
5-Three out of four outer shell electrons bond to two carbon atoms and one hydrogen atom
6-Three bonds in this plane are called sigma bonds
7-The 4th outer shell electrons are left in p orbitals above and below the plane of carbon atoms
8-The electrons in p orbitals overlap sideways to form a pi cloudy electron density above and below the plane of carbon atoms containing 6 electrons
9-The electrons density is spread around the ring and not localised to one carbon atom.

Question 4

State the shape and bond angle around carbon atoms in benzene ring

Answer 4

trigonal planar and 120 degrees

Question 5

How is delocalised ring of electrons formed in benzene

Answer 5

When 4th outer shell electrons in p orbitals of carbon atoms overlap sideways to form a pi bond above and below the plane of carbon atoms containing 6 electrons.

Question 6

why does benzene react by substitution reaction rather than addition reaction

Answer 6

1-Because reaction by addition is energetically unfavourable,
the product formed is less stable than benzene,
and the delocalisation is disrupted
2-However substitution reactions are energetically favourable,
the organic product formed retains its delocalisation ring,
therefore its stability