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Alevel Chemistry Edexcel > Topic 18 - Organic Chemistry 3 > Flashcards

Topic 18 - Organic Chemistry 3 Flashcards

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1
Q

What are arenes?

A

compounds containing a benzene ring

eg. phenol, nitrobenzene, etc

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2
Q

What is the molecular formula of benzene?

A

C6H6

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3
Q

What is the structure of benzene according to the Kekulé model?

A

6 carbon atoms in a ring with alternating single and double carbon-carbon bonds

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4
Q

What were the issues with the Kekulé model of benzene?

A
  • x-ray diffraction shows that benzene only has 1 carbon-carbon bond length but with the Kekulé model, you would expect two
  • IR spectrum has fewer peaks than expected for the Kekulé model
  • benzene does not undego electrophilic addition reactions, which you would expect it to if it had C=C bonds
  • enthalpy change of hydrogenation is much lower than expected for the Kekulé model (benzene is more stable)
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5
Q

What is the structure of benzene according to the delocalised model?

A
  • 6 carbon atoms in a ring where each carbon atom forms a sigma bond with its hydrogen and each neighbouring carbon and the remaining p-orbital forms a ring of delocalised electrons
  • p orbitals overlap above and below the molecule, forming a delocalised pi-electron system
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6
Q

benzene + oxygen →

A

carbon dioxide + water

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7
Q

benzene + bromine →

AlCl3/FeBr3 catalyst present

A

bromobenzene

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8
Q

What are the conditions for the halogenation of benzene?

A
  • dark

- AlCl3/FeBr3 catalyst (halogen carrier)

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9
Q

benzene + nitric acid →

sulfuric acid catalyst present

A

nitrobenzene + water

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10
Q

What is in a nitrating mixture?

A

conc nitric acid and conc sulfuric acid

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11
Q

What are the conditions for the nitration of benzene?

A
  • conc sulfuric acid catalyst

- 55°C

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12
Q

Why should the nitration of benzene be at 55°C?

A

to avoid multiple substitution of benzene

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13
Q

What is the purpose of using a nitrating mixture for the nitration of benzene?

A

it produces a stronger electrophile

-nitronium ion

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14
Q

What reaction happens in the nitrating mixture?

A

HNO3 + H2SO4 → NO2+ + HSO4- + 2H2O

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15
Q

What reaction happens to reform the catalyst after the nitration of benzene?

A

H+ + HSO4- → H2SO4

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16
Q

benzene + halogenoalkane →

AlCl3 catalyst

A

alkyl benzene + hydrogen halide

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17
Q

What conditions are needed for Friedel-Crafts alkylation (benzene and halogenoalkane)?

A
  • aluminium chloride catalyst

- heat under reflux

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18
Q

benzene + acyl chloride →

A

phenyl ketone + hydrogen chloride

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19
Q

What conditions are needed for Friedel-Crafts acylation (benzene and acylchloride)?

A
  • aluminium chloride catalyst

- heat under reflux

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20
Q

What is the molecular formula of phenol?

A

C6H6OH

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21
Q

What are the properties of phenol?

A
  • slightly acidic
  • not soluble
  • solid at room temp
  • more reactive than benzene
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22
Q

Why is phenol more reactive than benzene?

A

-phenol’s oxygen activates the benzene ring
-oxygen’s lone pair of e- are incorporated into the delocalised pi-electron system
-this increases electron density in the ring
-it can attract electrophiles more easily
(catalysts/halogen carriers not needed)

23
Q

phenol + bromine water →

A

2,4,6 tribromophenol + hydrogen bromide

24
Q

What are the properties of amines?

A
  • fishy smell
  • generally soluble (can H-bond with water)
  • have higher mp/bp than respective hydrocarbons
  • have basic nature (nitrogen’s lone pair of e- can accept H+)
25
Q

How does ammonia, primary aliphatic and primary aromatic amine’s basicity compare?

A

primary aliphatic amines > ammonia > primary aromatic amines

26
Q

Why are primary aliphatic amines more basic than ammonia and primary aromatic amines?

A
  • alkyl groups are e- pushing groups
  • this increases the nitrogen’s electron density
  • nitrogen can accept H+ more easily
27
Q

Why are primary aromatic amines less basic than primary aliphatic amines and ammonia?

A
  • NH2 is an activating group
  • nitrogen’s lone pair of e- are incorporated into the delocalised pi-electron system
  • nitrogen’s lone pair of e- are less accessible to accept H+
28
Q

amine + water →

A

ammonium salt + hydroxide ion

alkali soln

29
Q

amine + acid →

A

salt

30
Q

amine + acyl chloride →

A

N-substituted amide + hydrogen chloride

31
Q

primary amine + halogenoalkane →

A

secondary amine + ammonium halide

secondary amine can go on to react with halogenoalkane to form tertiary amine

32
Q

amine + copper(II) ions →

A

complex ions
[Cu(RNH2)4)]4+ (aq)
royal blue soln

33
Q

How can primary aliphatic amines be prepared?

A
  • halogenoalkane and excess ammonia + reflux

- reducing nitriles using lithium aluminium hydride in dry ether or hydrogen gas with a nickel catalyst

34
Q

How can primary aromatic amines be produced?

A

reducing nitrobenzene using tin and conc hydrochloric acid + reflux

35
Q

How are polyamides produced?

A

condensation polymerisation

dicarboxylic acid and diamine

36
Q

What is the general structure of an amino acid?

A
  • amine group (NH2)
  • carboxyl group (COOH)
  • variable region
37
Q

Why are amino acids optically active?

A

they have a chiral centre

except glycine

38
Q

What is a zwitterion?

A

when an amino acid’s amine group has been protonated and carboxy group has been deprotonated at the same time (at specific pH)

  • neutral (charges cancel)
  • solid at room temp (can form giant ionic lattices due to charges)
39
Q

How can amino acids be separated?

A

in chromatography

40
Q

How are dipeptides produced?

A

condensation reaction between two amino acids
-peptide bond formed
-water produced
(if dipeptides are joined, polypeptide if produced)

41
Q

How can a carbon chain length be increased?

A
  • using cyanide ions (can add one carbon)

- using Grignard reagents (can add multiple carbons)

42
Q

How are Grignard reagents prepared?

A

magnesium and halogenoalkane

in dry ether

43
Q

How are Grignard reagents used to produce an alcohol?

A

Grignard reagent is reacted with a carbonyl compound

  • aldehyde for primary/secondary alcohol
  • ketone for tertiary alcohol
44
Q

How are Grignard reagents used to produce a carboxylic acid?

A

Grignard reagent is reacted with carbon dioxide

45
Q

How are Grignard reagents used to produce an alkane?

A

Grignard reagent is reacted with water

46
Q

How can a carbon chain length be decreased?

A

using triodomethane reactions (iodine in alkali with strong acid)

47
Q

How is recrystallisation carried out?

A
  • compound is dissolved in minimum volume of hot solvent
  • it is then filtered hot and allowed to cool (in ice bath)
  • it is then filtered and washed with a small amount of cold solvent
  • crystals are dried between filter papers/using a Buchner funnel
48
Q

What is the purpose of recrystallisation?

A

to puridy solids

49
Q

How is drying carried out?

A
  • using a Buchner funnel and Buchner flask (suction filtration)
  • patting with filter paper
50
Q

How is melting/boiling point determination carried out?

A
  • sample is loaded into a capillary tube and placed in apparatus
  • temp is slowly increased and sample is observed
  • mp range is from when liquid begins to appear to when no solid is left
  • mp can be compared to known values
51
Q

What is the purpose of refluxing?

A

allows continuous heating so all of the reactants react

52
Q

What is the purpose of distillation?

A

separates liquids based on boiling points

53
Q

How is solvent extraction carried out?

A
  • impure product is dissolved in water/organic solvent and shaken
  • two layers (organic and aqueous layers) form in separating funnel and they can be run off
54
Q

How is purification by washing carried out?

A

impurity in organic product can be removed by adding another liquid which impurities react with

Alevel Chemistry Edexcel (19 decks)

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