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Chemistry A-Level > 6.1 aromatic compounds, carbonyls and acids > Flashcards

6.1 aromatic compounds, carbonyls and acids Flashcards

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1
Q

describe kekulé’s for benzene model using 3 points

A
  • sigma bonded ring
  • 3 alternating pi bonds
  • highly unsaturated
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2
Q

name 3 problems with kekulé’s benzene model

A
  • benzene is resistant to addition reaction and undergoes substitutions. suggests there aren’t double bonds
  • enthalpy of hydrogenation - benzene has lower enthalpy than predicted, value for benzene is LESS EXOTHERMIC
  • all 6 carbon bonds are the same length so all bonds must be uniform
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3
Q

how many pi electrons are there in the benzene ring?

A

6 pi electrons

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4
Q

describe the structure/bonding/delocalised system of benzene in 3 points

A
  • each C is sigma bonded to a H, forming a planar hexagonal ring
  • p orbitals overlap above and below the ring to make pi bonds
  • 6 electrons in pi bonds are delocalised around the ring
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5
Q

which mechanism does benzene undergo?

A

electrophilic substitution

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6
Q

describe the 3 steps of electrophilic substitution of benzene

A
  1. electron from benzene RING is accepted by the electrophile
  2. electrophile is bonded to a carbon with a hydrogen and the C-H bond is attracted to the plus in the middle of the broken benzene ring
  3. H+ is lost and remains as a product along with the benzene compound
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7
Q

what is halogenation?

A

substituting a halogen for a hydrogen on a benzene ring

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8
Q

what condition are required for a halogenation reaction?

A

halogen carrier catalyst

  • FeCl₃
  • AlCl₃
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9
Q

give the overall equation for the halogenation between benzene and chlorine

A

C₆H₆ + Cl₂ –> C₆H₅Cl + HCl

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10
Q

halogenation: give two equations showing the formation of an electrophile and the regeneration of the catalyst

A

forming electrophile:
Cl₂ + FeCl₃ –> FeCl₄⁻ + Cl⁺
regenerating catalyst:
H⁺ + FeCl₄⁻ –> FeCl₃ + HCl

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11
Q

what is nitration?

A

substituting a hydrogen for a nitronium ion -NO₂⁺ on a benzene ring

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12
Q

which reagents and conditions are required for the nitration reaction?

A

reagent: HNO₃
catalyst: concentrated H₂SO₄

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13
Q

give the overall nitration reaction

A

C₆H₆ + HNO₃ –> C₆H₅NO₂ + H₂O

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14
Q

nitration: give two equations showing the formation of the electrophile and the regeneration of the catalyst

A

formation of electrophile:
HNO₃ + H₂SO₄ –> NO₂⁺ + H₂O + HSO₄⁻
catalyst regen:
HSO₄⁻ + H⁺ –> H₂SO₄

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15
Q

what is a phenol molecule?

A

a benzene ring with an -OH attached to a carbon

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16
Q

what are friedel-crafts reactions?

A

reactions in which hydrogens are substituted with R groups on benzene

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17
Q

what is alkylation?

A

substituting a hydrogen for an akyl group on a benzene

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18
Q

how does alkylation occur? give the overall equation of the substitution of a methyl group to benzene

A

occurs like a halogenation reaction with same catalysts but reagent is a haloalkane
C₆H₆ + CH₃Cl –> C₆H₅CH₃ + HCl

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19
Q

give the functional group of an acyl chloride

A

RC=OCl

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20
Q

how can an acyl chloride be used in friedel-crafts reactions?

A

as a halogen carrier - the chlorine on the acyl group and the hydrogen on the benzene are removed and form HCl

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21
Q

list phenol, benzene and cyclohexene in order of electron density, from most dense to least dense

A

most - alkene
phenol
least - benzene

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22
Q

explain how phenol has a greater electron density than benzene

A

the lone pairs and p-orbital on the oxygen in the -OH group add to the delocalised of benzene and make it more electron dense

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23
Q

how does increased electron density in benzene, phenol and alkenes increase reactivity?

A

more electron density means the electrophile is more readily polarised and so is more likely to react

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24
Q

which two electrophilic subsitution reactions with pheno are you supposed to learn?

A

with Br

with DILUTE nitric acid

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25
Q

what conditions are required for both electrophilic substitution reactions of phenol? why are these condition required?

A

Br- NO catalyst - phenol is reactive enough

HNO₃ - no catalyst and DILUTE acid - phenol is more reactive and so doesn’t need as concentrated acid

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26
Q

what are the products formed from electrophilic substitution of phenol with bromine?

A

2,4,6-tribromophenol

multiple substitutions occur

27
Q

what are the products formed from electrophilic substitution of phenol with nitric acid?

A

mixture of 2-nitrophenol and 4-nitrophenol

28
Q

phenol is a ____ acid and _______ disassociates in water. phenol is a ____ acid than aliphatic alcohols becasue….

A
  • weak
  • partially
  • stronger acid than aliphatic alcohols because the ring weakens the O-H bond so H+ is easily lost
29
Q

give and a reversible equation demonstrating the weak acidity of phenol

A

C₆H₅OH(aq) —> C₆H₅O⁻(aq) + H⁺(aq)

30
Q

phenol + NaOH —> ?

A

—-> C₆H₅O⁻Na⁺ + water

makes salt-sodium phenoxide which is ionic and soluble in water

31
Q

phenol + Na —> ? how do they react? give a balanced eq

A

makes ionic salt, reacts vigorously, fizzing, sodium dissovles.
2C₆H₅OH + 2Na —> 2C₆H₅O⁻Na⁺ + H₂

32
Q

phenol does not react with __________.

A

metal carbonates

33
Q

what is a directing group? give 2 examples

A

a group on benzene that donates lone pairs into the benzene ring, giving a 2,4 directing effect
eg. -OH and -NH₂

34
Q

what is a withdrawing group? give to examples

A

a group that withdraws electron from benzene, making substitutions more common on 3 position
eg. -NO₂ and -COOH

35
Q

what kind of mechanism is the reduction of carbonyls?

A

nucleophilic addition

36
Q

what happens during a reduction of a carbonyl?

A

ketone/aldehyde becomes a secondary/primary alcohol

37
Q

what is the reagent used for the reduction of carbonyls? what is the nucleophile in the reaction?
what are the conditions?

A

reagent: NaBH₄
nucleophile is :H⁻ hydride ions
conditions: aqueous or alcoholic solution

38
Q

describe the mechanism of the reduction of carbonyls

A
  • curly arrow from hydride ion lone pair to C and curly arrow from C=O bond to O.
  • dipoles on C=O: C is delta+ and O is delta-
    INTERMEDIATE:
  • curly arrow from lone pair on O⁻⁻ to H on H₂O and curly arrow from H-O bond to O.
  • dipoles on H₂O: H is delta+ and O is delta-
39
Q

what products are formed from the reduction of carbonyls?

A

alcohol and HO⁻⁻

40
Q

what is Brady’s reagent and what is it used for? how does it work?

A

2,4-DNPH
used to identify ketones and aldehydes
forms ORANGE precipitate when reacted with aldehydes and ketones

41
Q

how can Brady’s be used to determine the exact original compound?

A
  • aldehydes and ketones have similar boiling points
  • reacting with Brady’s forms orange precipitates with distinct melting points
  • melting point can be compared to known values/database
42
Q

what is tollens reagent and what is it used for? how does it work?

A

it is ammoniacal silver nitrate and a mild oxidising agent
used for identifying aldehydes
only oxidises aldehyde and solid silver/silver mirror is formed

43
Q 
what are the carboxylic acid reaction with:
metal?
metal oxide?
metal hydroxide?
metal carbonate?
A
  • carboxylate salt + hydrogen
  • carboxylate salt + water
  • carboxylate salt + water
  • carboxylate salt + carbon dioxide
44
Q

what is the ester functional group?

A

-COO
C=O
|
O

45
Q

give the equation and conditions of esterification involving an alcohol

A

alcohol + carboxylic acid –> ester + water

under REFLUX and concentrated H₂SO₄ catalyst

46
Q

propanol + ethanoic acid?

A

propyl ethanoate + water

47
Q

pentanoic acid + butanol?

A

butyl pentanoate + water

48
Q

what is used to prepare esters that isn’t an alcohol or carboxylic acid?

A

acid anhydride
O=C-O-C=O
| |
R. R..

49
Q

give the esterificiation equation using the acid anhydride (CH₃CO)₂O and methanol

A

methanol + ethanoic anhydride –> methyl ethanoate + ethanoic acid

50
Q

give the general equation of forming esters with acid anhydrides

A

alcohol + acid anhydride –> ester + carboxylic acid

51
Q

how does the esterification occur between an acid anhydride and alcohol?

A

the OH group loses an O to the C in the acid anhydride and forms an ester group
the H on the OH group goes to the O where the anhydride was broken and forms the COOH

52
Q

what products are obtained in the acid and alkali hydrolyses of esters?

A

acid: original products (alcohol and carboxylic acid)
alkali: carboxylate salt (COO⁻) forms and original alcohol

53
Q

what is the functional group of an acyl group?

A

COCl

54
Q

give the general equation of the formation of acyl chlorides

A

carboxylic acid + SOCl₂ –> acyl chloride + SO₂ + HCl

55
Q

describe how an acyl chloride formed

A
  • Cl on SOCl₂ swaps with the OH on the COOH group
  • the O from the OH goes to SO₂
  • the H from the OH and the Cl go to the HCl
56
Q

how do you name acyl chlorides?

A

longest chain length + oyl chloride

eg. ethanoyl chloride or butanoyl chloride

57
Q

acyl chloride + water?

A

carboxylic acid + HCl

58
Q

acyl chloride + alcohol?

A

ester + HCl

59
Q

acyl chloride + amine?

A

primary amide + NH₄Cl or HCl

60
Q

acyl chloride + primary amine?

A

secondary amide + NH₄Cl or HCl

61
Q

what can phenol not do with regard to esterification?

A

phenol cannot react with carboxylic acids to form an ester

62
Q

give the esterification general equation involving phenol

A

acyl chloride + phenol –> phenol ester + HCl

more vigorous than carboxylic acid + alcohol

63
Q

are electrophiles + or - ?

A

electrophiles = positive

64
Q

are nucleophiles + or - ?

A

nucleophiles = negative

Chemistry A-Level (13 decks)

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