Aromatic Compounds Flashcards
What is the molecular formula of benzene?
C6H6
What is the state of benzene at room temperature?
Liquid
What is the bond angle of benzene?
bond angle = 120 degrees
What are the 3 features of benzene that don’t support Kekule’s model?
- benzene is resistant to addition reactions
- enthalpy change of hydrogenation of benzene is more stable that predicted
- all the carbon bonds are same length
What technique was used to find the bond lengths of benzene?
X ray diffraction
What happens to the 4th electron in the p-orbital of each carbon atom in benzene?
It delocalises to form rings of electron density above and below the hexagon, forming rings of delocalised electron density above/ below the hexagon.
How do the rings of electron density affect the stability of Benzene?
Makes benzene very stable, even though it is unstable (aromatic stability)
Why does benzene have a relatively high melting point?
Close packing of flat hexagonal molecules when solid.
Is benzene soluble in water? Explain why?
No because it is non polar.
Dangers of benzene — why is it not used in schools?
It is a carcinogen.
How do you name compounds containing a benzene ring?
-benzene, or phenyl- ; can designate position on ring using numbers if there is more than one substituent.
Why is benzene attacked by electrophiles?
High electron density above/ below ring due to delocalised electrons.
Nitration of benzene is what type of reaction?
Electrophilic substitution reaction.
Which ion is used to nitrate benzene?
NO2(+)
What is the catalyst in nitration of benzene?
Sulphuric acid
What type of catalyst is used for a Friedel-Crafts reaction?
A halogen carrier (e.g. AlCl3)
Why does benzene not react directly with halogens?
The aromatic ring is too stable.
What is happening when AlCl4(-) is formed in terms of electrons?
The lone pair of electrons on the chlorine atom is forming a coordinate bond to Al
How could you use a Friedel-Crafts mechanism to add a methyl group to a benzene ring?
Use a halogenoalkane and AlCl3 to create an electrophile that can attack benzene
What reactions can you carry out to show the weak acidity of phenol?
A neutralisation reaction with NaOH occurs but absent when you react phenol with carbonates.
What is the relative ease of electrophilic substitution of phenol compared to benzene and why?
It is easier for electrophilic substitution to occur with phenol because oxygen lone pair of electron from the -OH group are partially delocalised into ring therefore this increases the electron density of the ring thus electrophiles are more attracted to phenol
What is the directing effect of electron donating groups OH and NH2?
They direct groups to the 2 and 4 position.
What is the directing effect of electron withdrawing groups such as NO2?
NO2 directs atoms to the 3 position of the ring
