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Flashcards in Paper 4 Deck (82):
1

Arene

Hydrocarbon containing one or more benzene ring

2

Why does Kekule's proposed ring not work?

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

3

How is bromobenzene formed?

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

4

How is nitrobenzene formed?

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

5

Describe the bonding in benzene

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

6

Compare the reactivity of benzene and cyclohexene (alkene)

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

7

Why does benzene undergo substitution and not addition?

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

8

Compare the reactivity of benzene and phenol

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

9

How is 2,4,6-tribromophenol formed?

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

10

How is sodium phenoxide formed?

Phenol + NaOH
Phenol + Na > + 1/2 H2

11

Phenol uses

Antiseptic, disinfectants, detergents, preparation of aspirin
WEAK ACID

12

Primary amine

A H atom on ammonia has been replaced by an alkyl or aryl (R) group 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

13

How do amines react?

WEAK BASES
So react with acids > salts

14

How do you prepare an aliphatic amine?

NUCLEOPHILIC SUBSTITUTION
CH3CH2CH2Cl + NH3 > CH3CH2CH2CH2NH2 + HCl
Propylamine

15

Aliphatic

In a chain

16

Aromatic

Contains a benzene ring

17

How do you prepare an aromatic amine?

Nitrobenzene + Sn + c.HCl
Heat under reflux with [H]

18

Synthesis of diazonium salt

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

19

Synthesis of an azo dye

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

20

Aldehyde

RCHO
-al

21

Ketone

R'COR
-one

22

Alkyl

Alkane with a H atom removed

23

Aryl

Cyclic compound containing benzene ring

24

Oxidation of a primary alcohol

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

25

Oxidation of an aldehyde

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

26

Oxidation of a secondary alcohol

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

27

Reduction of carboxylic acid, aldehyde or ketone

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

28

Brady's reagent

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

29

Silver mirror

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

30

Carboxylic acid

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

31

Esters

RCOOR'
Perfumes, food flavourings, oils

32

Formation of esters

1. RCOOH + R'OH (c.H2SO4) RCOOR' + H2O
2. Acid anhydride + alcohol > ester + CA

33

Hydrolysis of esters

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

34

Triglyceride

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

35

Order of healthiness of fats (healthiest first)

Polyunsaturated
Monounsaturated
Trans
Saturated

36

Why are trans fats bad?

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

37

Why are monounsaturated an polyunstaurated fats good?

Bad LDL cholesterol sticks to artery walls causing build up
Good HDL cholesterol carries bad cholesterol away

38

What is biodiesel?

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

39

What is carbon neutral?

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

40

What is an amino acid?

RCH(NH2)COOH
Basic amine group + acidic carboxyl group

41

Zwitterion

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

Isoelectric point

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

43

In acidic conditions, what happens to an amino acid?

Acts as a base > N+H3

44

In alkaline conditions, what happens to an amino acid?

Acts as an acid > COO-

45

Peptide link

-C=ON-H-
Formed by condensation reactions

46

Hydrolysis of polypeptides or dipeptides

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

Addition polymerisation

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

48

Condensation polymerisation

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

49

Polyesters

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

50

Terylene (PET)

Strong, flexible and abrasion resistant > clothes
Benzene-1,4-dicarboxylic acid + ethane-1,2-diol

51

Poly(lactic acid)

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

52

Polyamides

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

53

Nylon-6,6

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

54

Kevlar

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

55

Hydrolysis of polymers

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

56

Photodegradable polymers

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

Biodegradable polymers

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

58

Isomers

Compounds with the same molecular formula but different arrangements of atoms

59

Structural isomerism

Different structural formula
- Positional (functional group)
- Chain branch
- Functional group

60

Stereoisomerism

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

Racemic mixture

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

62

Optical isomer synthesis

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

Chromatography

An analytical technique used to separate the components in a mixture

64

Mobile phase

Sweeps over stationary phase in a definite direction

65

Stationary phase

Fixed in place - interacts with components, slowing them down

66

Solid stationary phase separates by...

Adsorption > onto surface > stronger adsorption = more slowed

67

Liquid stationary phase separates by...

Relative solubility > greater solubility = more slowed

68

Thin-layer chromatography

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

Rf value

distance moved by component/distance moved by solvent front

70

Difficulties of TLC

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

71

Gas chromatography

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

Retention time

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

73

Difficulties of GC

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

74

GC-MS

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

Mass spec

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

76

IR spec

Functional groups

77

NMR spec

low energy radio frequency radiation waves used

78

Chemical shift

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

Why are denuterated solvents used

Instead of H solvents so no H2 peaks

80

Carbon NMR

C environments = chemical shift
Benzene look for mirrors

81

Proton NMR

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

82

MRI

NMR spec