6.1.1: Aromatic compounds Flashcards

1
Q

What is the structure and formula of Benzene?

A

C6H6

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2
Q

What is the empirical formula of benzene?

A

CH

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3
Q

What is the state of benzene at room temperature?

A

liquid

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4
Q

What is the bond angle of benzene?

A

Bond angle = 120 degrees

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5
Q

What are the 3 features of benzene that don’t

support Kekule’s model?

A

● Benzene is resistant to addition reactions
● Enthalpy change of hydrogenation of benzene is more stable than predicted
● All the carbon bonds are same length

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6
Q

What technique was used to find the bond lengths of

benzene?

A

X ray diffraction

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7
Q

What happens to the 4th electron in the p-orbital of

each carbon atom in benzene?

A

It delocalises to form rings of electron
density above and below the hexagon,
forming rings of delocalised electron
density above/below the hexagon.

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8
Q

How do the rings of electron density affect the

stability of Benzene?

A

Makes benzene very stable, even though

it is unsaturated (aromatic stability)

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9
Q

Why does benzene have a relatively high melting

point?

A

Close packing of flat hexagonal

molecules when solid

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10
Q

Is benzene soluble in water? Explain why?

A

No because it is non polar

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11
Q

Dangers of benzene - why it is not used in schools?

A

It is a carcinogen

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12
Q

How do you name compounds containing a benzene

ring?

A

-benzene, or phenyl- ; can designate
position on ring using numbers if there is
more than one substituent

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13
Q

Why is benzene attacked by electrophiles?

A

High electron density above/below ring

due to delocalised electrons

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14
Q

Nitration of benzene is what type of reaction?

A

Electrophilic substitution reaction

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15
Q

Which ion is used to nitrate benzene?

A

NO2+

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16
Q

What is the catalyst in nitration of benzene?

A

Sulfuric acid

17
Q

How is this NO2+ ion generated? (conditions and

equations)

A

Concentrated H2SO4 and concentrated HNO3.
H2SO4 + HNO3 → H2NO3+ + HSO4-
H2NO3+ → H2O + NO2+
Overall: H2SO4 + HNO3 → HSO4- + NO2+ + H2O

18
Q

How is the H2SO4 catalyst regenerated in the nitration of benzene?

A

HSO4- + H+ → H2SO4

H+ from benzene ring

19
Q

Write an overall equation for

the nitration of benzene.

A

C6H6 + HNO3 → C6H5NO2 + H2O

20
Q

What type of catalyst is used for a Friedel-Crafts

reaction?

A

A halogen carrier (e.g. AlCl3)

21
Q

Why does benzene not react directly with halogens?

A

The aromatic ring is too stable

22
Q

What is happening when AlCl4- is formed in terms of electrons?

A

The lone pair of electrons on the chlorine atom is forming a coordinate bond to Al

23
Q

How is the AlCl3 catalyst reformed?

A

AlCl4- + H+ → HCl + AlCl3

(H+ from benzene)

24
Q

How could you use a Friedel-Crafts mechanism to

add a methyl group to a benzene ring?

A

Use a halogenoalkane and AlCl3 to
create an electrophile that can attack
benzene

25
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
26
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
27
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
28
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