Structure Of Benzene

Question 1

Draw kekules model

Describe the bonds within it and explain

Answer 1

Search it
C-C 0.154nm
C=C 0.134nm
So double bond is smaller than single. But the bond is continuously changing between double and single

Question 2

What happend to the knowledge on the side lengths after experimention

Answer 2

Found out they are 0.140nm which is in-between the 2 sides

Question 3

Draw the molecular model and explain each part

Answer 3

Draw
Pi + sigma bonds
Sigma bonds - 3 of them 2 for C-C and 1 for C-H and as one e- left for each carbon it all attaches together to form a delocalised system (pi ring) this makes the overall molecule stable

Question 4

Show that a benzene with a pi ring is more stable than one without it

Answer 4

Kekules model
1 double bond + H2 -> -120 kjmol-1 ( enthalpy change )
3 doubl bonds + 3H2 -> -360kjmol-1 (enthalpy change)

Molecular model
Benzene ring + 3H2 -> -208kjmol-1 ( so in reality this has a lower enthalpy change as it’s more thermodynamicly stable)

Question 5

Are bonds making and breaking endo or exo

Answer 5

Make = exo
Break = endo

Question 6

Show benzene ring is more table when beining made than a double bond

Answer 6

6C + 3H2 ->
Ring (+51kjmol-1)
Double bond (+215kjmol-1)

So the calculated enthalpy change of formation is lower as it’s thermodynamicly stable