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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
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

Chemistry A2 (4 decks)

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