Benzene

Question 1

Describe the structure of benzene

Answer 1

-Cyclic
-Planar
-C6H6

Each carbon has a lone electron in a p-orbital that sticks out of the planar ring.

Question 2

What do the lone electrons in benzene form?

Answer 2

Delocalised ring, share and distribute the electrons equally around the ring.

Question 3

What does the delocalised electron structure mean for the length of the C-C bonds?

Answer 3

All the same length of around 139pm.

Somewhere between a single and double bond length.

Question 4

How do we measure the stability of benzene?

Answer 4

Enthalpy change of hydrogenation (adding hydrogen)

Question 5

Why is benzene more stable than its theoretical structure cyclohexa-1,3,5-triene?

Answer 5

Benzene = -208
Theoretical= -360
(enthalpy of hydrogenation)

-Takes more energy to break bonds in benzene, so more stable
-Due to delocalised electron structure.
-And bond lengths are all the same

Question 6

What is an arene?

Answer 6

Aromatic compounds, molecules that contain a benzene ring.

Question 7

In what cases would you use ‘benzene’ at the end of a name?

Answer 7

-Attached to a halogen
-Attached to a CH3

e.g Bromobenzene, Nitrobenzene, 1,2-dimethylbenzene

Question 8

In what cases would you use ‘phenyl’ at the start of the name for benzene?

Answer 8

-Attached to an alcohol group
-Attached to an amine

e.g Phenol, Phenylamine

Question 9

When arenes react they go through what mechanism?

Answer 9

Electrophilic substitution

Question 10

Why is benzene attractive to electrophiles?

Answer 10

High electron density of delocalised electron ring.