6.1.1: Aromatic compounds Flashcards
What is the structure and formula of Benzene?
C6H6
What is the empirical formula of benzene?
CH
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 than 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 unsaturated (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 it is 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?
Sulfuric acid
How is this NO2+ ion generated? (conditions and
equations)
Concentrated H2SO4 and concentrated HNO3.
H2SO4 + HNO3 → H2NO3+ + HSO4-
H2NO3+ → H2O + NO2+
Overall: H2SO4 + HNO3 → HSO4- + NO2+ + H2O
How is the H2SO4 catalyst regenerated in the nitration of benzene?
HSO4- + H+ → H2SO4
H+ from benzene ring
Write an overall equation for
the nitration of benzene.
C6H6 + HNO3 → C6H5NO2 + H2O
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 is the AlCl3 catalyst reformed?
AlCl4- + H+ → HCl + AlCl3
(H+ from benzene)
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 electrons from
the -OH group are partially delocalised into ring
therefore this increases the electron density of the
ring thus electrophiles are more attracted phenol
What is the directing effect of electron donating groups OH and NH2?
They direct group to the 2 and 4 position of the ring in electrophilic substitution of aromatic compounds
What is the directing effect of electron withdrawing group NO2?
NO2 directs atoms to the 3 position of the ring in electrophilic substitution of aromatic compounds
