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Chemistry Module 6 > Benzene/Aromatic Compounds > Flashcards

Benzene/Aromatic Compounds Flashcards

1
Q

How do you name benzene when the functional group is on the ring?

A

‘Name of functional group’ ‘benzene’

eg Nitrobenzene

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2
Q

How do you name benzene when there’s an alkyl chain up to 6 carbons?

A

‘Name chain’ ‘yl’ ‘benzene’

eg pentyl benzene

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3
Q

How do you name benzene when there’s an alkyl chain over 6 carbons?

A

‘Phenyl’ ‘name of chain’

Phenyl heptane

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4
Q

How do you name benzene when the functional group is not directly on the ring?

A

‘phenyl’ ‘name of functional group’ (may also need numbers)
eg 2-chloro-1-phenyl propane
Phenyl ethanone

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5
Q

What are the priorities when naming benzene?

A 
Phenol
Methyl benzene
Phenyl amine
Benzaldehyde
Benzoic acid
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6
Q

What is phenol?

A

OH directly bonded to benzene

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7
Q

What is methyl benzene?

A

CH3 directly bonded to benzene

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8
Q

What is phenyl amine?

A

NH2 directly bonded to benzene

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9
Q

What is benzaldehyde?

A

Ethanal directly bonded to benzene

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10
Q

What is benzoic acid?

A

Methanoic acid directly bonded to benzene

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11
Q

Why is there spare electrons in the p orbitals of carbon in benzene?

A

Each carbon has 4 electrons in the outer shell, 2 make sigma bonds with C, 1 is used to make a sigma bond with H, so 1 is spare

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12
Q

What is the shape around the carbon atoms in benzene?

A

120 trigonal planar

This makes benzene flat

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13
Q

What is the definition of a pi bond in benzene?

A

Sideways overlap of p orbitals on adjacent carbon atoms above and below the plane of carbon atoms in a ring.
6 electrons in pi bond across 6 C-C, delocalised

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14
Q

What are the negatives of kekule’s model of benzene?

A

Bond length
Isomers
C=C
Enthalpy of hydrogenation

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15
Q

How is bond length a negative of kekule’s model of benzene?

A

C=C are shorter so should be 2 different bond lengths but an X-ray diffraction shows all C-C bonds are all the same length in benzene

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16
Q

How are isomers a negative of kekule’s model of benzene?

A

2Br can be on the same double bond or on different ones. Tested in a number of environments you would expect different results but they react the same

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17
Q

How is the C=C a negative of kekule’s model of benzene?

A

Adding Br2 when there are double bonds makes the solution go from orange to colourless so, using kekule’s model, benzene should do this addition reaction BUT in order to get the benzene to do this you need a catalyst and it does a substitution reaction

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18
Q

How is the enthalpy of hydrogenation a negative of kekule’s model of benzene?

A

A ring with 1 C=C = -120KJ
A ring with 2 C=C = -240 KJ
So you would expect Kekule’s model to be -360KJ BUT, benzene only has an enthalpy of hydrogenation of -208KJ
Less exothermic than Kekule’s model so it is more stable

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19
Q

What is the molecular/emperical formula for benzene?

A

Molecular - C6H6

Empirical - CH

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20
Q

What can you add to benzene?

A 
Cl
Br
Acyl chloride
R group
NO2
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21
Q

What is the catalyst when adding Cl to benzene?

A

AlCl3/FeCl3

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22
Q

What is the catalyst when adding Br to benzene?

A

AlBr3/FeBr3

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23
Q

What is the catalyst when adding a COR to benzene?

A

AlCl3/Br3 or FeCl3/Br3

24
Q

What is the catalyst when adding an R group to benzene?

A

AlCl3/Br3 or FeCl3/Br3

25
What is the catalyst when adding NO2 to benzene?
Conc H2SO4 | 50 degrees celsius
26
How do you work out the electrophile when adding something to benzene?
Whatever you are adding with a + | Br+, Cl+ etc
27
What is the reagent when adding Cl to benzene?
Cl2
28
What is the reagent when adding Br to benzene?
Br2
29
What is the reagent when adding NO2 to benzene?
Conc HNO3
30
What is the reagent when adding an R group to benzene?
R-halogen
31
What is the reagent when adding COR to benzene?
Acyl chloride | R-CO-Cl
32
What are the 4 steps for the mechanism of reacting things with benzene?
Overall equation Make electrophile Curly arrow Regenerate catalyst
33
What is different about phenols pi bond compared to benzene and why?
It has an extended delocalised system. Because O and C have p orbitals. The lone pair on O is partially delocalised into pi bond which increases the electron density (8e- over 6C-C)
34
What is an aromatic alcohol?
When OH is directly bonded to a benzene ring
35
How is phenol a weak acid? (pH 3-6)
H+ ions don't fully dissociate / the acid partially dissociates to release H+ ions in aqueous solution
36
What can phenol react with?
``` Alkali (NaOH) Metals (Na) Up to 3 Br2 Dilute HNO3 Conc HNO3 ```
37
What does adding an alkali (NaOH) to phenol make?
Salt and H2O
38
What does adding a metal (Na) to phenol make?
Salt and H2
39
What does adding up to 3Br2 to phenol make?
Up to 2,4,6-tribromo phenol
40
What is made when adding dilute HNO3 to phenol?
Nitro phenol | NO2 either on 2 or 4 in the ratio 1:2
41
What is made when adding conc HNO3 to phenol?
Di/tri nitro phenol
42
What is observed when adding an alkali to phenol?
No fizzing (water is made)
43
What is observed when adding a metal to phenol?
Fizzing (H2 gas is produced)
44
What is observed when adding bromine to phenol?
Orange to colourless solution | White precipitate formed
45
Compare phenol and benzene
Phenol has H bonds with itself Phenol has 8e- across 6C-C benzene has 6e- Phenol has higher electron density in pi bond Phenol can react with Br2 at room temp with no catalyst as it can induce dipoles on it Phenol attract electrophiles more readily
46
Compare alkenes and benzene
Alkenes have 2e- across 1C=C benzene has 6e- Alkenes have higher electron density in pi bond Alkenes can react with Br2 at room temp with no catalyst as it can induce dipoles on it Alkenes attract electrophiles more readily
47
What are the 3 directing groups?
NO2 NH2 OH These have priority unless other info is given
48
Describe NO2 as a directing group
3,5 directing, electron withdrawing
49
Describe NH2 as a directing group
2,4,6 directing, electron donating
50
Describe OH as a directing group
2,4,6 directing, electron donating
51
When are things 2,4,6 directing?
Most electronegative element is directly on the ring (N in NH3 and O in OH)
52
When are things 3,5 directing?
Most electronegative element is 1 away from the ring (O in NO2)
53
How do you go from NO2 to NH2?
Sn, conc HCl, heat under reflux
54
What type of reaction is mainly used with benzene?
Electrophilic substitution
55
How can you distinguish between phenol and other acids?
Phenol won't react with a carbonate, no fizzing | Acids will react and fizzing would occur

Chemistry Module 6 (10 decks)

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