benzene Flashcards

1
Q

What is benzene

A

C6H6

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2
Q

Properties of benzene

A

Highly flammable
Sweet-smelling
Found naturally in crude oil
A carcinogen

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3
Q

Is benzene reactive or unreactive

A

unreactive

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4
Q

What are arenes

A

hydrocarbons based on benzene

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5
Q

similarities between Kekule and delocalised model

A
  • overlap of p orbitals

- Pi bond above and below

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6
Q

diffrences beterrn kekule and delocalised model

A
  • kekuke has alternating pi bonds,localised electrons

- delocalised pi electrons spread around ring

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7
Q

3 pieces of evidence supporting delocalised model of benzene

A
  • bond length is not single of double bond length
  • Hydrogenation is less exothermic than expected
  • benzene does not react with bromine
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8
Q

-OH with benzene ring name

A

phenol

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9
Q

-NH2 with benzene ring name

A

phenylamine

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10
Q

why is it harder for benzene to react with bromine

A

The delocalised electrons above and below the plane are very stable.

  • spread out the negative charge
  • addition reaction would break ring
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11
Q

what can a halogen carrier be used to do

A

add a halogen atom onto the benzene ring

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12
Q

Types of halogen carrier

A

AlCl3 or FeBr3

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13
Q

What are acyl chlorides

A

like COOH but OH replaced by Cl

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14
Q

Why is phenol less soluble than water

A

presence of a non polar benzene ring

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15
Q

What type of acid is a phenol

A

Weak acid

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16
Q

alcohols, phenol, carboxylic acid acidity from least to most

A

Alcohol,phenol,carboxilyic acid

17
Q

How can you show phenol is a weak acid

A

Reacts with strong base (NAOH), doesnt react with carbonates

18
Q

How to distinguish between a phenol and carboxylic acid

A

React with sodium carbonate, carboxilyic acid will make CO2

19
Q

What does phenol and bromine make

A

2,4,6 tribromophenol and HBR

20
Q

What does the nitration of phenol produce

A

2 and 4 nitro phenol and water

21
Q

Why are phenols more reactive than benzene

A

lone pair of electrons from the oxygen p-orbital donated to the pi system of the phenol. Increases electron density, attracts electrophiles more strongly

22
Q

What directing group is the -NH2 group

23
Q

What directing group is the -NO2 group

24
Q

What is the alkylation of benzene

A

sub of a hydrogen atom to an alkyl

25
Why are all carbon carbon bonds the same length in a benzene
Each carbon atom forms single covalent bonds to the carbon on either side All the carbon carbon bond lengths r the same
26
How do rings form around benzene
Unpaired electron on each carbon atom is in a p orbital that sticks out above and below the plane The p orbitals on each carbon atom combine to form a ring of delocalised electrons
27
What does a lower enthalpy change for benzene mean
More energy needed to break the bond than the other so less reactive
28
When is phenyl used to name benzene
attached to an alkyl chain with a functional group or 7 or more carbon atoms
29
COOH attached to a benzene name
benzoic acid
30
CHO attached to benzene name
benzaldehyde
31
A student adds bromine water to a solution of phenol. | What would the student see during this reaction?
Bromine water goes from orange to colourless and a white precipitate is formed.
32
What is the number of sigma bonds in a benzene molecule?
12
33
Difference between Kekule and delocalised in terms if a pi bond
Kekule - 3 pi bonds with 2 electrons localised | -delocalised - 1 pi ring with 6 electrons