Chapter 18 Flashcards
What is Benzene?
A compound with the formula C6H6 which has a cyclic structure with its six carbon atoms joined together in a ring
What are the two ways of representing Benzene?
The Kekule model and the delocalised model
What is the Kekule model of Benzene?
Each carbon atom was bonded to one hydrogen atom and the molecule was constantly flipping between 2 isomers by switching over the double and single bonds
What was the biggest problem with the Kekule model?
X-ray diffraction studies showed that all the carbon-carbon bond lengths were the same, which went against the idea of single and double bonds
In the delocalised benzene model, how many sigma bonds does each carbon form?
3, meaning each carbon has 1 remaining p-orbital
What do the remaining p-orbital from each carbon in benzene do?
They overlap sideways, to form a ring of pi-bonds which make up to clouds above and below the plane of carbon atoms. The electrons in these clouds are delocalised and do not belong to a specific carbon atom
How did the enthalpy change of hydrogenation provide more evidence for the delocalised model of benzene?
More energy was required to break the bonds in Benzene than the kekule model predicted, due to the extra stability of benzene, due to the delocalised ring of electrons
How do alkenes react with bromine?
They react easily with bromine water via electrophillic addition, which decoularises the bromine water from brown to colourless. The bromine atoms are added across the C=C double bond.
Why is benzene unwilling to undergo electrophillic addition reactions, unlike benzene?
The delocalised ring spreads out the negative charge, making benzene very stable, and unwilling to undergo addition reactions and destroy the stable ring
What mechanism does benzene prefer to react by?
Electrophillic addition
How does Benzene burn?
With a smoky flame, producing carbon dioxide and water, and a lot of the carbon stays as soot.
What are aromatic compounds?
Compounds containing a Benzene ring
How does benzene react with an electrophile?
Via an electrophilic substitution reaction
Benzene breaks the delocalised ring to react with the electrophile, forming an unstable intermediate, where the C-H bond breaks restoring the benzene ring
How can an electrophile be made into a stronger electrophile?
Using a halogen-carrier catalyst, which accepts a lone pair of electrons from a halogen atom on an electrophille, making the electrophile stronger and able to react with the benzene ring
How do you form bromobenze?
React benzene with Br2 and a halogen carrying catalyst (e.g. FeBr3) which pulls a lone pair of electrons from the reacting bromine atom to make the other bromide atom a stronger electrophile
What does fiedel-craft alkylation do?
It puts any alkyl group onto benzene using a halogenoalkane and a halogen carrier catalyst`
What does fiedel-craft acylation produce?
Ketones
How do you produce a phenylketone?
You reflux benzene with an acyl chloride
What carbocation is formed from the acyl choride and the AlCl3?
AlCl4- + CH3CO+
How do you form nitrobenzene?
Heat benzene with nitric acid, using sulfuric acid as a catalyst.
When forming nitrobenzene, what is the reaction between nitric acid and sulfuric acid?
H2SO4 + HNO3 –> HSO4- + H2NO3+
H2NO3+ —> NO2 + + H20
What is phenol?
A benzene ring with the -OH group attached
Why is phenol more reactive than benzene?
One of the lone pairs from the oxygen atom overlaps with the delocalised pi-bonds from the ring, so is partially delocalised into the pi system, increasing the electron density of the ring, increasing its ability to attract electrophiles
What happens if you shake phenol with orange, bromine water?
It will react, decolorizing the orange colour, smelling of antiseptic
