6.1.1- Aromatic Compounds Flashcards
What is formula of Benzene?
C6H6
What is empirical formula of benzene?
CH
What is state of benzene at room temperature?
Liquid
What is the bond angle of benzene?
120 degrees
What are the features of benzene that don’t support Kekule’s model?
- Benzene is resistant to addition reactions
- Enthalpy of 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 benzne?
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
What ion is used to nitrate benzene?
NO2+
What is the catalyst in nitration of benzene?
Sulfuric acid
How is the NO2+ ion generated? (conditions and equations)
Concentrated H2SO4 and HNO3
H2SO4 + HNO3 -> H2NO3+ + HSO4-
H2NO3+ -> H2O + NO2+
Overall: H2SO4 + HNO3 -> HSO4- + NO2+ + H2O
How is the H2SO4 catalyst regenerated in nitration of benzne?
HSO4- + H+ -> H2SO4 (H+ from benzene ring)
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 haloalkane 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 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 to phenol
What is the direction effect of electron donating groups OH and NH2?
They direct 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
