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Chemistry A2 > Paper 4 > Flashcards

Paper 4 Flashcards

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1
Q

Arene

A

Hydrocarbon containing one or more benzene ring

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2
Q

Why does Kekule’s proposed ring not work?

A
  1. Doesn’t react like alkenes eg does not decolourise bromine without a catalyst - no electrophilic addition
  2. Bond lengths - X-ray crystallography shows all bond lengths are equal when double bonds are actually shorter than single bonds
  3. Hydrogenation of benzene is less exothermic than expected (-360 vs -208) suggesting benzene is actually more stable
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3
Q

How is bromobenzene formed?

A

Benzene + Br2 + AlBr3 (halogen carrier)
AlBr3 + Br2 > AlBr4- + Br+ (electrophile)
H+ + AlBr4- > AlBr3 + HBr
ELECTROPHILIC SUBSTITUTION

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4
Q

How is nitrobenzene formed?

A 
Benzene + c.HNO3 + c.H2SO4
Reflux 50degrees
Higher temp = further subst.
H2SO4 + HNO3 > H2NO3+ + HSO4-
H2NO3+ > NO2+ + H2O
H+ + H2SO4 > H2SO4
ELECTROPHILIC SUBSTITUTION
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5
Q

Describe the bonding in benzene

A

Each carbon forms 3 sigma bonds
1 electron left in a p-orbital on each carbon
P-orbitals overlap to form a delocalised pi-system
Electrons are delocalised above and below ring
C-C bond lengths equal
Ring is planar

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6
Q

Compare the reactivity of benzene and cyclohexene (alkene)

A

Benzene is less reactive towards bromine (needing a catalyst)
The delocalised pi-system means the electrons are spread out
So benzene has a lower electron density than a double bond in which the pi-electrons are localised
Therefore is less attractive to electrophiles and is less able to polarise them

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7
Q

Why does benzene undergo substitution and not addition?

A

The delocalised pi-system means the electrons are spread out
This reduces repulsion between them and gives benzene extra stability
Substitution allows the delocalised pi-system to be retained
Addition would permanently disrupt the delocalised pi-system

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8
Q

Compare the reactivity of benzene and phenol

A

Phenol is more reactive than benzene eg does not need a catalyst to react with bromine
In phenol the ring is activated
The lone pair of electrons in a p-orbital on the oxygen is delocalised into the ring
This increases the electron density in the ring
Making it more attractive to electrophiles and more able to polarise them

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9
Q

How is 2,4,6-tribromophenol formed?

A

Phenol + 3Br2
Br+ + Br- > 3HBr
White ppt - orange bromine decolourises

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10
Q

How is sodium phenoxide formed?

A

Phenol + NaOH

Phenol + Na > + 1/2 H2

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11
Q

Phenol uses

A

Antiseptic, disinfectants, detergents, preparation of aspirin
WEAK ACID

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12
Q

Primary amine

A

A H atom on ammonia has been replaced by an alkyl or aryl (R) group > RNH2

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13
Q

How do amines react?

A

WEAK BASES

So react with acids > salts

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14
Q

How do you prepare an aliphatic amine?

A

NUCLEOPHILIC SUBSTITUTION
CH3CH2CH2Cl + NH3 > CH3CH2CH2CH2NH2 + HCl
Propylamine

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15
Q

Aliphatic

A

In a chain

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16
Q

Aromatic

A

Contains a benzene ring

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17
Q

How do you prepare an aromatic amine?

A

Nitrobenzene + Sn + c.HCl

Heat under reflux with [H]

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18
Q

Synthesis of diazonium salt

A

Phenylamine + Nitrous acid (Sodium nitrite and XS HCl)
Less than 10degrees
NaNO2 + HCl > HNO2 + NaCl

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19
Q

Synthesis of an azo dye

A

Diazonium salt + phenol in alkaline conditions (>Sodium phenoxide)
Azo group = N=N
Bright orange ppt
Used as a dye in paints

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20
Q

Aldehyde

A

RCHO

-al

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21
Q

Ketone

A

R’COR

-one

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22
Q

Alkyl

A

Alkane with a H atom removed

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23
Q

Aryl

A

Cyclic compound containing benzene ring

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24
Q

Oxidation of a primary alcohol

A

ROH + [O] > RHO + H2O
Heat gently and distill
Acidified potassium dichromate (Cr2O72-/H+; K2Cr2O7 + H2SO4; orange > green Cr3+)

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25
Q

Oxidation of an aldehyde

A

RHO + [O] > ROOH + H2O
Heat under reflux
Acidified potassium dichromate (Cr2O72-/H+; K2Cr2O7 + H2SO4; orange > green Cr3+)

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26
Q

Oxidation of a secondary alcohol

A

RCOHR’ + [O] > RCOR’ +H2O
Heat gently
Acidified potassium dichromate (Cr2O72-/H+; K2Cr2O7 + H2SO4; orange > green Cr3+)

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27
Q

Reduction of carboxylic acid, aldehyde or ketone

A 
Warm + H2O (solvent)
\+NaBH4
Sodium tetrahybridborate (III) > H-
2[H]
NUCLEOPHILIC ADDITION
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28
Q

Brady’s reagent

A

2,4-DNP
Forms an orange ppt with aldehydes and ketones
Recrystallize and can ID derivatives from melting points of known k/a

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29
Q

Silver mirror

A

Tollens’ reagent/ammonical silver nitrate [Ag(NH3)2]+ warm gently in a water bath - SM forms with aldehydes only as oxidised. Ag reduced.

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30
Q

Carboxylic acid

A 
RCOOH
Highly polar bonds
Soluble in water up to 4 Cs
Weak acids
Partially dissociate
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31
Q

Esters

A

RCOOR’

Perfumes, food flavourings, oils

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32
Q

Formation of esters

A
  1. RCOOH + R’OH (c.H2SO4) RCOOR’ + H2O

2. Acid anhydride + alcohol > ester + CA

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33
Q

Hydrolysis of esters

A
  1. Reflux with dilute H2SO4/HCl
    ester + water (H+) CA + alcohol
  2. Reflux with alkali
    ester + NAOH > Sodium salt + alcohol
34
Q

Triglyceride

A

A triester of propane-1,2,3-triol (glycerol) + octa/hexadecanoic acid (fatty acid) > all 3 groups esterified + 3H2O

35
Q

Order of healthiness of fats (healthiest first)

A

Polyunsaturated
Monounsaturated
Trans
Saturated

36
Q

Why are trans fats bad?

A

Pack together more closely that cis - solid - block arteries > CHD

37
Q

Why are monounsaturated an polyunstaurated fats good?

A

Bad LDL cholesterol sticks to artery walls causing build up

Good HDL cholesterol carries bad cholesterol away

38
Q

What is biodiesel?

A

Veg/animal fat - long alkyl esters used in diesel engines/blended with petrodiesel
Trigylceride + 3H3OH > 3H3COC=OR + COHCOHCOH

39
Q

What is carbon neutral?

A

Same amount of CO2 absorbed when growing as released when burned as a fuel
But less food > starvation

40
Q

What is an amino acid?

A

RCH(NH2)COOH

Basic amine group + acidic carboxyl group

41
Q

Zwitterion

A

A dipolar ionic form or an amino acid that is formed by the donation of a hydrogen ion from the carbonyl group to the amino group. Because both charges are present, there is no overall charge.

42
Q

Isoelectric point

A

The pH value at which the amino acid exists as a zwitterion

43
Q

In acidic conditions, what happens to an amino acid?

A

Acts as a base > N+H3

44
Q

In alkaline conditions, what happens to an amino acid?

A

Acts as an acid > COO-

45
Q

Peptide link

A

-C=ON-H-

Formed by condensation reactions

46
Q

Hydrolysis of polypeptides or dipeptides

A
  1. ACIDIC - heat under reflux with 6moldm-3 HCl for 24 hours
    (+H2O + 2H+) > H3N+- + -COOH
  2. ALKALINE - heat with NaOH at just above 100degrees
    (+NaOH) > -COO-Na+ + H2N-
47
Q

Addition polymerisation

A

Double C=C bond in alkene opens and monomers join, requiring catalyst and polymer is the only product

48
Q

Condensation polymerisation

A

Formed from condensation reactions between monomers. Small molecule (H2O/HCl) also produced

49
Q

Polyesters

A

Dicarboxylic acid + diol > -C=OC- ester link

50
Q

Terylene (PET)

A

Strong, flexible and abrasion resistant > clothes

Benzene-1,4-dicarboxylic acid + ethane-1,2-diol

51
Q

Poly(lactic acid)

A

Derived from corn-starch
Biodegradable and renewable
Can be made into containers, stitches, wast5e sacks and packaging.
2-hydroxypropanoic acid (lactic acid)

52
Q

Polyamides

A

Dicarboxylic acid + diamino (NH2) > -C=ON-H- amide link

53
Q

Nylon-6,6

A

Clothing, airbags, hoses, conveyer belts, tyres, ropes
v strong, elastic and abrasion-resistant
1,6-diaminohexane + hexanedioic acid

54
Q

Kevlar

A

Bulletproof vests
V strong + light, 5x stronger than steel, stiff
Benzene-1,4,diamine + Benzene-1,4-dicarboxylic acid

55
Q

Hydrolysis of polymers

A
  1. BASIC (polyesters)
    Hot 2nNaOH/H2O > O-Na+ + diol
  2. ACIDIC (polyamides)
    H+/2nH2O + H2SO4 catalyst > H3N+ + dioic acid
56
Q

Photodegradable polymers

A

Weak and brittle when exposed to light > blended with light-sensitive additives catalysing breakdown on polymer in UV radiation/ + C=O, absorbing light energy and breaking > waxy compounds > (bacteria) CO2 + H2O

57
Q

Biodegradable polymers

A

> CO2 + H2O
eg poly(lactic acid) from maize
Poly(glycolic acid) from cane sugar and unripe grapes - stitches
Replace oil bases products = bioplastics

58
Q

Isomers

A

Compounds with the same molecular formula but different arrangements of atoms

59
Q

Structural isomerism

A

Different structural formula

  • Positional (functional group)
  • Chain branch
  • Functional group
60
Q

Stereoisomerism

A

Different arrangement of atoms in space

  • E/Z isomerism - lack or rotation around C=C bond > trans/E/180 degrees and cis/Z/90degrees
  • Optical isomerism - non-super imposable mirror images due to chiral carbons (4 different groups attached to central carbon). Produce chemically identical isomers that rotate plane polarised light in opposite directions)
61
Q

Racemic mixture

A

A mix containing 50/50 each optical isomer (enantiomer) - no effect on plane-polarised light because the rotations cancel each other

62
Q

Optical isomer synthesis

A

In the lab, racemic mixtures are formed
Naturally occurring amino acids and most sugars are optically active but only one enantiomer is found in natural systems
Drug must be right shape to fit in active site - only one enantiomer. Other may fit in another active site, have no effect or cause harmful side effects.
Chiral drugs must be made to contain only one enantiomer - half dosage needed, side effects reduced and pharmalogical activity is improved.
Difficult and expensive:
- natural enzymes and bacteria produce one
- chemical chiral synthesis

63
Q

Chromatography

A

An analytical technique used to separate the components in a mixture

64
Q

Mobile phase

A

Sweeps over stationary phase in a definite direction

65
Q

Stationary phase

A

Fixed in place - interacts with components, slowing them down

66
Q

Solid stationary phase separates by…

A

Adsorption > onto surface > stronger adsorption = more slowed

67
Q

Liquid stationary phase separates by…

A

Relative solubility > greater solubility = more slowed

68
Q

Thin-layer chromatography

A

Monitors extent of a chemical reaction/checks purity of compounds
SP = thin layer of adsorbent such as silica gel on a flat solid support = TLC plate
MP = liquid solvent

69
Q

Rf value

A

distance moved by component/distance moved by solvent front

70
Q

Difficulties of TLC

A

Similar components have similar Rf values
Unknown = no Rf for comparison
Difficult to find one solvent to separate all components

71
Q

Gas chromatography

A

Used to separate volatile components in a mix
SP = thin liquid/solvent on inside of capillary tubing
MP = carrier gas moving through column (inert)

72
Q

Retention time

A

The time taken for a component to pass from column to detector - area under peak = amount of compound

73
Q

Difficulties of GC

A

Many may have same retention time
Not all separated and detected - may ‘hide’
No reference for unknown

74
Q

GC-MS

A

GC separates by doesn’t identify conclusively
MS detailed info but no separation
Together = more powerful tool
Mass spectra compared with database for identification
Used in forensics, environmental analysis, airport security and space probes

75
Q

Mass spec

A

Mr = parent ion (M+) and peaks due to fragmentation

76
Q

IR spec

A

Functional groups

77
Q

NMR spec

A

low energy radio frequency radiation waves used

78
Q

Chemical shift

A

compares frequency of NMR absorption with frequency of reference peak of TMS at 0ppm
Reference signal = tetramethylsilane TMS - used to calibrate against TMS reference peak

79
Q

Why are denuterated solvents used

A

Instead of H solvents so no H2 peaks

80
Q

Carbon NMR

A

C environments = chemical shift

Benzene look for mirrors

81
Q

Proton NMR

A

Number of peaks, chemical shift, relative peak area, splitting pattern (n+1)

82
Q

MRI

A

NMR spec

Chemistry A2 (4 decks)

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