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Chemisty A level > Phenols > Flashcards

Phenols Flashcards

1
Q

What is a phenol structure?

A

an aromatic benzene ring with an -OH group attached directly

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2
Q

What state is phenol at room temp?

A

solid

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3
Q

Why is phenol solid at room temp unlike liquid alcohols?

A

phenol is a bigger molecule with a bigger contact surface area so it has more london forces that need to be broken to melt it

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4
Q

Why is phenol only slightly soluble?

A

has an -OH group which can form H bonds with water
but it has a much larger non-polar hydrocarbon part which cannot form H bonds
the H bonding effect is outweighed by the hydrophobic aromatic ring

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5
Q

What is the acidity of phenol like?

A

a very weak acidity - only a small proportion is ionised

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6
Q

What is phenols molecular formula?

A

C6H5OH

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7
Q

why is phenol more acidic than water and ethanol?

A

when H+ dissociates from an acid, it leaves behind a negative ion = the more stable this ion is the more favourable the dissociation will be (more acidic)

the (-) of the phenoxide ion is spread out in the pi system making the ion more stable

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8
Q

Do phenols react better with strong or weak bases?

A

strong bases like -OH

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9
Q

What is the reaction of phenol with NaOH?

A

C6H5OH + NaOH —-> C6H5O(-) Na(+) + H2O

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10
Q

what type of structure does C6H5O(-) Na(+) have?

A

ionic - simple molecular

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11
Q

What 2 weak base ions does phenol NOT react with?

A

carbonate - CO3 (2-)
hydrogen carbonate ions - HCO3 (-)

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12
Q

What test is used to distinguish between a phenol or carboxylic acid?

A

reacting with carbonate or hydrogen carbonate ions
phenol = will not react
carboxylic acid = fizzing

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13
Q

Why does phenol undergo electrophilic substitution more easily than benzene?

A

the ring in phenol is said to be activated by the -OH group because:

a lone pair of electrons on oxygen is delocalised into the pi system of the ring = increases electron density in the aromatic ring, making it more attractive to an electrophile
The OH is said to be an electron donating group

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14
Q

Where is electron density increased the most on phenol?

A

the 2, 4 and 6 positions

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15
Q

What is observed when phenol reacts with bromine?

A

bromine is decolourised
white precipitate - 2,4,6 - tribromophenol

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16
Q

What are the 2 electron-donating groups?

A

-OH and -NH2

17
Q

How do electron-donating groups affect electrophilic substitution?

A

increase reactivity of the ring = higher electron density so ring is more attractive to an electrophile
they direct substitution reactions to take place at the 2,4 and 6 positions

18
Q

What is an electron-withdrawing group?

A

a group of atoms attached to the benzene ring which decreases the electron density in an aromatic ring to which it is bonded

19
Q

What is an example of an electron-withdrawing group?

A

-NO2

20
Q

What effects do electron-withdrawing groups have on electrophilic substitution?

A

decrease the reactivity of the ring = lower electron density = less atrracted to electrophile
if strongly deactivating like -NO2, they direct substitution reactions to take place at the 3 position
reaction must take place with a halogen carrier catalyst

21
Q

What is the pH of phenol roughly?

A

pH 5-6 = weak acid

22
Q

What is deduced from the reaction of phenol with NaOH?

A

phenol acts as an acid by donating a H+ to the NaOH therefore it is a weak acid

23
Q

What is deduced about phenol from reacting it with DILUTE nitric acid?

A

dilute = more reactive as benzene, does not require a fume cupboard like benzene
doesnt require an acid catalyst for nitration so phenol is more reactive

24
Q

How would you test if an alkene or phenol is present?

A

add HNO3 as alkenes do not react and phenols form an orange precipitate

25
Q

Why is phenol more reactive than benzene?

A

the p-orbitals on the oxygen atom in the phenoxide ion become delocalised in the pi-electron system in the benzene ring. This increases electron density of the delocalised pi-system making it more attractive to electrophiles and polarising electrophiles

26
Q

What are all the reactions with phenol you need to know with naming the products?

A

Br2 (aq) = 2,4,6-tribromophenol
NaOH = sodium phenoxide and water
dilute nitric acid = nitrophenol (2 products 1st or 4th position = 1st position is major product)
strong base reactions
carbonates (weak bases = no reaction

27
Q

Why is the OH in phenol called an activating group?

A

it donates electrons into the benzene ring = increases reactivity of phenol

28
Q

What is the directing effect?

A

electron donating groups like OH and NH2 direct substituents towards the 2,4 and 6 posititon on the benzene ring

29
Q

What is an example of electron withdrawing groups?

A

NO2

30
Q

what is the directing effect of electron withdrawing groups?

A

carbon 3

Chemisty A level (30 decks)

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