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Edexcel Chemistry A level > Organic 3 > Flashcards

Organic 3 Flashcards

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1
Q

Describe the modern structure of benzene

A
  • formula of C6H6
  • six C atoms in a hexagonal ring and one H atom bonded by single sigma bonds.
  • 6 p electrons delocalised in a ring structure above and below the plane of carbon atoms.
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2
Q

Describe kekule’s structure of benzene

A
  • alternate single and double covalent structures between carbon atoms (starts with double)
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3
Q

What does it suggest if benzene is a planar molecule?

A
  • all C-C bonds are the same length, and have a bond length and strength somewhere between the C-C and C=C bond
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4
Q

Explain how X‑ray diffraction shows that benzene has a delocalised structure and
not a Kekulé structure

A
  • Shows that all C-C bonds are the same length
  • in the Kekule structure, C=C bonds would have been shorter.
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5
Q

describe the enthalpy of hydrogenation of the kekule vs benzene vs cyclohexane structure, and how it shows that benzene is more stable than both.

A
  • cyclohexane enthalpy = -120
    so kekule will be 3x-120= -360 (expected)

But in reality, the value ended up being around -208, so less exothermic than expected.
When represented on an energy level diagram, it shows that benzene is the most thermodynamically stable.

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6
Q

What type of reactions does benzene usually go through?
Why?

A
  • electrophilic substitutions
  • electron density is not high enough to induce a dipole, so cannot go through addition reactions.
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7
Q

why is methylbenzene more reactive than benzene?

A
  • methyl side group releases electrons into the delocalised system making it more attractive to nucleophiles.
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8
Q

Name the following for the reaction with benzene and halogens.
- change in functional group
- reagent
- conditions
- mechanism

A
  • benzene to halobenzene
  • halogen
  • iron halide catalyst
  • Electrophilic substitution
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9
Q

Name some observations when benzene burns.
What effects this observation?

A
  • burns with a very sooty flame
  • carbon to H ratio - the lower this is, the more sooty the flame will be.
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10
Q

Give the equations to form electrophiles Cl+ and Br+ from AlCl3 and FeBr3

A
  • AlCl3 + Cl2 —> AlCl4- + Cl+
  • FeBr3 + Br2 —> FeBr4- + Br+
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11
Q

Describe the mechanism for the halogenation of benzene

A
  • curly arrow going from middle of electron ring to electrophile (the Br+/Cl+ etc)
  • Curly arrow going from MIDDLE of bond to electron ring (which now has a + sign in the middle with only 3/4 of it actually drawn.)
  • Forms a halobenzene (with halogen sticking out from an edge of a benzene ring)
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12
Q

Name the following for the nitration of benzene
- change in functional group
- reagent
- conditions
- mechanism

A
  • benzene —> nitrobenzene
  • Conc nitric acid in the presence of conc H2SO4 (catalyst)
  • 60 Degrees
  • Electrophilic substitution
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13
Q

Give the equation to form the electrophile NO2+ for nitration of benzene.

A
  • HNO3 + 2H2SO4 —> NO2+ + 2HSO4- + H3O+
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14
Q

What is the usefulness of the nitrification of benzene?

A
  • important to manufacture explosive material, or formation of amines which are used to manufacture dyestuffs.
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15
Q

Name the following for the hydrogenation of benzenes
- change in functional group
- reagent
- conditions
- type of reaction

A
  • benzene –> cyclohexane
  • Hydrogen
  • nickel catalyst, 30 atm, 200 degrees.
  • addition and reduction
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16
Q

Name the following for the Friedal Crafts Alkylation
- change in functional group
- reagent
- conditions
- mechanism

A
  • benzene to alkyl benzene
  • chloroalkane in the presence of anhydrous aluminium chloride catalyst.
  • heat under reflux
  • electrophilic substitution
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17
Q

give the equation for the electrophile CH3CH2+

A

AlCl3 + CH3CH2Cl —-> Ch3CH2+ + AlCl4-

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18
Q

Name the following for the Friedal Crafts acylation
- change in functional group
- reagent
- conditions
- mechanism

A
  • benzene to phenyl ketone
  • acyl chloride in presence of a anhydrous AlCl3 catalyst
  • heat under reflux
  • electrophilic substitution
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19
Q

Give the equation to form the electrophile CH3C=O+

A

AlCl3 + CH3COCl –> CH3CO+ + AlCl4-

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20
Q

Why are Friedel Craft reactions important/useful?

A
  • produce a reactive functional group on the benzene ring, which is otherwise unreactive, which can then be used to produce dyestuffs etc.
  • this allows the molecule to carry out subs in milder conditions.
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21
Q

Name 2 properties of phenols

A
  • very weakly acidic
  • will react with sodium metal and NaOH but NOT Na2CO3
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22
Q

Name the following for the reaction of phenol with Bromine
- change in functional group
- reagent
- conditions
- observations

A
  • no change - will only add Brs.
  • Bromine water
  • room temp
  • white solid forms
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23
Q

Compare the reaction of benzene with bromine and phenol with bromine

A
  • phenol does not need a FeBR3 catalyst
  • goes through MULTIPLE substitution reactions, whereas benzene will only undergo a single substitution reaction.
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24
Q

Name 3 uses of phenols

A
  • plastics
  • antiseptics
  • paint resins
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25
Q

explain why electrophilic subs are more likely with phenols rather than benzene.

A
  • the overlap of the -OH group and orbital.
  • electrons in the p-orbital of the oxygen overlaps with the delocalised ring structure of benzene, so they become partially delocalised into the pi-system
  • therefore, the electron density increases within the ring, and so is more susceptible to attack from nucleophiles.
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26
Q

What is the functional group of an amine?

A

N atom with a lone pair - can get primary, secondary, tertiary, quaternary ions and aromatic amines, which are ‘N substituted’ when it is secondary or above.

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27
Q

What are the two ways of making aliphatic amines?

A
  • reacting halogenoalkane with excess ammonia
  • reducing a nitrile
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28
Q

Name the following for the reaction of halogenoalkne with ammonia
- change in functional group
- reagent
- conditions
- mechanism
- product

A
  • C-X to NH2
  • excess ethanolic ammonia
  • heat and pressure
  • nucleophilic sub
  • forms a primary amine and ammonium halide salt.
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29
Q

What is a disadvantage of making aliphatic amines using the halogenoalkane method?
Why?

A
  • product is not pure, as it produces salts (primary, secodnary, teritary, quaternary) as well.
  • because the primary amine will still have a lone pair on the N, so it can still act as a nucleophile.
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30
Q

Name the following for the reaction of reduction of nitriles
- change in functional group
- reagent
- conditions
- mechanism
- product

A
  • NO2 to NH2
  • Hydrogen Gas and nickel catalyst
  • High temp and pressure
  • Primary amine ONLY.
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31
Q

Give the functional group of amides

A

C=O-NH2 (with the Hs being subbed in for R groups)

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32
Q

Give 2 properties of amines

A
  • fishy smell
  • can form H bonds with water (the N and the H)
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33
Q

Give 2 characteristics of primary aliphatic amines
Give the reasons for these properties.

A
  • act as Bronsted lowry bases (act as proton acceptors) because lone pair on the N can form dative bond with H+ ions.
  • are stronger bases than ammonia because alkyl groups are electron releasing and push electrons towards the N, making it a stronger base.
34
Q

name one property of secondary aliphatic amines

A
  • stronger bases than primary amines, as they have more subbed in alkyl groups, so more electrons are pushed onto the N atom
35
Q

Give one property of aromatic amines

A
  • do not form basic solutions.
  • this is because lone pair on the N delocalises with the delocalised ring on benzene, so the N is less able to accept protons.
36
Q

what is the product of the reaction between acids and amines?

A
  • ammonium salts
37
Q

What is the product of NaOH and ammonium salts?

A

amine

38
Q

how to make a basic buffer from amines?

A

weak base and salt of the weak base
eg methlyamine and methylammonium chloride

39
Q

Name the following for the reaction between an acyl chloride and primary amine
- reagent
- conditions
- product

A
  • primary amine
  • room temp
  • secondary amide
40
Q

Name the following for the reduction of nitroarenes
- reagent
- conditions
- mechanism
- products

A
  • Sn and HCl
  • heating
  • reduction
  • phenylamine
41
Q

Name the following for the reaction of an acyl chloride with a primary amine
- change in functional group
- reagent
- conditions
- mechanism

A
  • acyl chloride to secondary amide
  • primary amine
  • room temp
  • nucleophilic addition-elimination
42
Q

what type of reaction is involved in making a polyamide?

A
  • condensation polymerisation
43
Q

What is the side product for polymerisation involving an acyl chloride

A
  • HCl
44
Q

What can be used to hydrolyse polyamides?

A
  • NaOH
45
Q

True or false:
Polyamides have Hydrogen bonds between the N and C on adjacent molecule

A

FALSE
they are between H and O of adjacent molecules

46
Q

What are the func groups on an amino acid?

A
  • NH2 and COOH
47
Q

What is a zwitterion?

A
  • an ion with a permanent dipole on either side - the H3N+, and COO-
48
Q

Is the amine group acidic or basic?

A

basic

49
Q

is the carboxyl group acidic or basic?

A

Acidic

50
Q

Describe what will happen if an amino acid is placed into an acidic solution

A
  • the carboxyl group will gain H+ ions, but the amine group will stay the same (H3N+)
51
Q

Describe what will happen if an amino acid is placed into a basic solution

A
  • the amine group will loose a H+ ion.
52
Q

Give a method to calculate the Rf value of a amino acid.

A
  • chromotography paper, draw pencil line from the bottom
  • (general method)
  • spray paper with ninhydrin and put in oven.
  • calc by doing distance moved by amino acid/distance moved by solvent
53
Q

Why is ninhydrin sprayed onto the chromatography paper?

A
  • amino acids are transparent, so doing this allows red and blue spots to appear.
54
Q

Describe the optical activity of amino acids, and any exceptions

A
  • every amino acid except glycine is optically active, and will rotate plane-polarised light.
55
Q

What bond is formed in proteins?

A
  • peptide
56
Q

What reagent is used to hydrolyse proteins into their constituent amino acids?

A
  • HCl or NaOH (dilute acids or bases)
57
Q

Describe how to prepare Grignard reagent

A
  • dissolve halogenoalkane in dry ether, then react with magnesium
58
Q

Grignard and methanal product

A

primary alcohol

59
Q

Grignard with other aldehydes

A

secondary alcohols

60
Q

Grignard with ketones

A

tertiary alcohols

61
Q

Grignard with CO2

A

carboxylic acid

62
Q

Give 3 ways in which the carbon chain length can be increased

A
  • halogenoalkane reacted with KCN
  • producing hydroxynitriles from carbonyls
  • reacting with a grignard reagent.
63
Q

state the colour change observed when alcohols are oxidised to aldehyde/ketone

A

orange to green

64
Q

When is reflux used?
why is reflux useful?

A
  • when heating organic reaction mixtures for a long time
  • prevents volatile compounds from escaping (eg organic vapours) by condensing them back to liquids.
65
Q

How to convert alkene into dihalogenoalkane under what conditions?

A
  • Cl2, Br2, I2 etc
  • room temp
66
Q

How to convert ketone/aldehyde to hydroxynitrile?

A
  • HCN in the presence of KCN.
67
Q

How to convert aldehyde to carboxylic acid?

A
  • acidified K2Cr2O7
  • heat under reflux
68
Q

How to convert acyl chlorides to esters?

A
  • react with alcohol at room temp
69
Q

How to convert acyl chlorides to primary amide?

A

react with NH3 at room temp

70
Q

How to convert acyl chlorides to carboxylic acids?

A
  • hydrolysis reaction with water
71
Q

How to convert acyl chlorides to secondary amide?

A
  • react with primary amide.
72
Q

How to convert nitrile to amine?

A
  • reduction with LiAlH4
73
Q

How to convert alkene to diol?

A
  • steam and phosphoric acid catalyst
  • at 60 atm and 300 degrees Celsius
74
Q

How to convert alcohol to halogenoalkane?

A
  • PCl5/NaBr and H2SO4/red phosphorus and I2
  • heat under reflux
75
Q

How to convert halogenoalkane to alcohol?

A
  • ## react with NaOH and H20,warm
76
Q

How to convert nitrile to carboxylic acid?

A
  • acid hydrolysis
  • heat with HCl
77
Q

How to convert halogenoalkane to amine?

A
  • NH3,
    heat
78
Q

How to convert Halogenoalkane to carboxylic acid in 2 step synthesis

A
  • Mg in dry ether,(grignard reagent) and then react product with CO2 in diltue acid
79
Q

Explain why the filter paper and funnel are warmed in an oven before gravity filtration
(2)

A
  • to make sure solution doesn’t cool down significantly
  • this could decrease premature crystals forming during filtration
80
Q

Explain why 1. cooling and recrystalising and 2. filtering the crystals under reduced pressure purifies the product.

A
  • the product is less soluble in colder solvent
  • reduced pressure allows more soluble impurities to be filtered out.
81
Q

What are 2 words that describe the Grignard reagent?

A
  • nucleophile
  • reducing agent
82
Q
A

Edexcel Chemistry A level (18 decks)

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