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Chemistry A Level > 18 - Organics III > Flashcards

18 - Organics III Flashcards

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1
Q

what is the Kekulé model of benzene

A
  • 6 carbon ring with 3 double bonds
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2
Q

what is the delocalised model of benzene

A
  • overlap of 6 p orbitals to form a pi system
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3
Q

evidence of the delocalised model

A
  • through x ray diffraction, found to be a perfect hexagon so can’t be Kekulé as double bonds are shorter than single
  • enthalpy of hydration of benzene is less exothermic than expected, due to its extra stability due to the delocalised electrons increasing its entropy
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4
Q

benzene and bromination

A
  • resistant to electrophilic addition and instead does electrophilic substitution
  • delocalised pi bonds in benzene vs dlocalised electron density in alkenes
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5
Q

melting points of benzene compared to methylbenzene

A

methylbenzene much lower as the methyl group prevents good packing

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6
Q

reaction of benzene with oxygen in air

A

combustion, gives a very sooty flame as the C:H ratio is very high

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7
Q

mechanism of benzene with bromine

A
  • check mechanism
  • AlBr3 catalyst
  • eventually goes from orange to colourless
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8
Q

why is AlBr3 a good catalyst

A

aluminium is electron deficient as it has only 6 valence electrons

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9
Q

mechanism of benzene with nitric acid and sulfuric acid

A
  • check mechanism

- T < 50°C prevents too many substitutions and TNT is explosive

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10
Q

mechanism of Friedel-Crafts alkylation

A
  • check mechanism

- bromoalkane and AlBr3 catalyst

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11
Q

mechanism of Friedel-Crafts acylation

A
  • check mechanism

- acyl chloride and AlCl3 catalyst

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12
Q

why does benzene undergo electrophilic substitution

A
  • benzene has high electron density above and within the ring
  • can easily donate electrons from the pi system
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13
Q

relative reactivity of phenol compared to benzene

A
  • phenol more reactive as the two lone pairs from the Os are donated into the ring
  • creates more electron repulsion in the ring so more likely to be donated
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14
Q

relative stability of phenol compared to benzene

A
  • phenol more stable as the lone pairs on the Os delocalise into the ring, spreading the charge
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15
Q

phenol acid

A
  • draw dissociation
  • phenoxide ion more stable due to delocalisation of negative charge
  • weak and only reacts with OH-
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16
Q

mechanism of bromination of phenol

A
  • check mechanism

- solid product as it’s a large molecule and breaks more hydrogen bonds than it makes

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17
Q

bromination of phenol vs benzene

A 
phenol:
- fast
- bromine WATER
- room temp
3 substitutions
benzene:
- slow
- need to heat and add AlBr3 catalyst
- one substitution
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18
Q

what is the amine functional group

A

N in a carbon chain

19
Q

solubility and boiling points of primary, secondary and tertiary amines

A

1° and 2° have higher boiling points and solubility as they can hydrogen bond
3° still soluble as they have lone pair

20
Q

bad way to make an amine

A

R - Br + NH3 –> R-NH2 + HBr

  • nucleophilic substitution
  • check mechanism
  • can’t prevent multiple substitutions
21
Q

good way to make an amine

A
  • reduction of a nitrile

- LiAlH4 in dry ether

22
Q

reduction of nitrobenzene with equations

A
  • conc, HCl (aq)
  • Sn
  • heat under reflux
  • add NaOH
  • check equation
23
Q

amine + water equation

A
  • forms alkaline solution
  • reversible reaction
  • NH2 part + H+ –> NH3+ group
  • very basic so reacts with any acid
24
Q

amine + HCl

A

check salt

25
Q

amine + water

A

check salt

26
Q

amine + propanoic acid

A

check salt

27
Q

how to make an amide

A

amine + acyl chloride –> amide + HCl

28
Q

amine + ethanoyl chloride

A

check reaction

29
Q

amine + halogenoalkane

A

check reaction

30
Q

amine + Cu(II) ions

A

check complex ion

31
Q

relative basicities of ammonia, primary amines and aminobenzene

A
  • aminobenzene weakest as the lone pair delocalises into ring, making it less likely to donate to H+
  • NH3 middle
  • primary amine strongest as R group pushes electrons towards the N lone pair, more repulsion so more likely to donate
32
Q

what is the amide functional group

A
  • C = O
    |
    N
33
Q

melting and boiling points of amides

A

higher than carboxylic acids and very high, two lone pairs on O and lone pair on N can do hydrogen bonding

34
Q

chemistry of amides, bonds

A

lone pair on N delocalises into C = O, reducing δ+ on C and strengthening pi bond

35
Q

formation of polyamides

A
  • condensation polymerisation

- always release HCl or H2O

36
Q

draw repeat unit of dicarboxylic acid and diamine

A

check

37
Q

draw repeat unit of diacyl chloride and diamine

A

check

38
Q

draw repeat unit of amino acid polyamide

A
  • check

- form peptide bond

39
Q

functional group of an amino acid

A

craboxylic acid with an amino side group

40
Q

acidity and solubility of amino acids (draw)

A
  • H from OH dissociates and joins NH2 to make NH3+ and OH- in solution (draw)
  • form zwitterions
  • gives them acidic and basic properties
  • very high aqueous solubility as water can hydrate the +ve and -ve charges
  • form ionic compounds, white crystalline solid with high melting point
41
Q

draw amino acid + NaOH and HCl

A

check

42
Q

charge of amino acids in solution

A

mixture of both ions, so never neutral

43
Q

chirality of amino acids

A
  • all chiral unless R group is H

- rotate plane polarised light in equal angles in opposite directions

44
Q

hydrolysis of peptide bond (draw)

A
  • heat under reflux
  • HCl (aq) or NaOH(aq) and water
  • amino acids produced which can be separated by chromotography
  • check products with HCl and NaOH

Chemistry A Level (14 decks)

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