Aromatic compounds Flashcards
What is the formula of benzene?
C6H6
What is the structure of benzene called?
Planar cyclic structure
Describe the structure of benzene?
Each carbon atom forms single covalent bonds to the carbons on either side of it and to one hydrogen atom, the final unpaired is located in the p-orbital
Why are the electrons in a benzene ring said to be delocalised?
They don’t belong to a specific carbon atom
What length are the bonds in a benzene ring?
140 pm
What is the order of bond lengths for bonds in a benzene ring, a single C-C bond and a double C=C bond?
Shortest; C=C at 135 pm
Middle; Benzene at 140 pm
Longest; C-C at 147 pm
Explain how experimental data shows that benzene is more stable than the theoretical compound cyclohexa-1,3,5-triene.
Cyclohexa-1,3,5-triene has one double bond and the enthalpy of hydrogenation is -120 kjmol-1.
The expected for benzene with three double bonds would be -360 kjmol-1.
The actual enthalpy of hydrogenation for benzene is -208 kjmol-1 = 152 kjmol-1 less exothermic than expected
More energy must have been put in to overcome the bonds in benzene, showing its more stable
When is an aromatic compound named “-benzene” ?
The benzene ring is the main functional group and the molecule is named as a substituted benzene ring, eg. Methylbenzene
When is an aromatic compound named “Phenyl-“ ?
When the benzene ring is not the main functional group, eg with an OH group it would be phenol
How do you number a benzene ring if the functional groups are the same?
Choose one and count either clockwise or anticlockwise, whichever will give you the smallest numbers
How do you number a benzene ring if the functional groups are different?
Start from which group gives the molecules its suffix and count around whichever way will give smallest numbers.
If no suffix from a functional group, do it alphabetically
