CD - Benzene and Delocalisation

Question 1

features of benzene:

Answer 1

• regular, planar hexagon
• all bond angles are 120˚
• c-c bonds are all the same length

Question 2

what does the delocalised modle of benzene suggest?

Answer 2

• each carbon atom has 4 electrons which can be used to create other bonds - 3 of these are used to form sigma ond to either h or c
• the 6 delocalised e- spread out evenly so that theyre shared by all 6 Cs
• these electrons form a delocalised charged cloud ABOVE AND BELOW PLANE OF THE MOLECULE

Question 3

why is the delocalised structure of benzene considered stable?

Answer 3

due to its planar cyclic structure and number of electrons the delocalisation in benzene is particuarly stable

doesnt readily undergo reactions that would disrupt this delocalisation

Question 4

thermochemical data that suggests Kekule modle is incorrect:

Answer 4

enthalpy of hydrogenation for C=C is -120kjmol-1
however for 3 C=C it is -208kjmol-1 this is 152kjmol-1 less then the kekule modle suggests

so the thermochemical data of provides good evidence that the delocalised model is a much better description

Question 5

molecular geometry that suggests Kekule modle is incorrect:

Answer 5

kekule modle has all bond angles at 120˚ but the alternating c-c and c=c would be at different lengths to eachother
therefore the kekule structure would not actually be a regular hexagon (c-c would be longer)