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A-level Chemistry > Module 6 - Organic Chemistry and Analysis > Flashcards

Module 6 - Organic Chemistry and Analysis Flashcards

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1
Q

What is a chiral carbon atom?

A

It’s one which has four different groups attached to it. It’s possible to arrange the groups into two different ways around the carbon atom so that two different molecules are made - called enantiomers or optical isomers

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2
Q

What are enantiomers?

A

They are mirror images of each other and can’t be superimposed. If a molecule can be superimposed on its mirror image, it’s achiral and it doesn’t have an optical isomer

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3
Q

What are optical isomers?

A

They are optically active, they rotate plane-polarised light. One enantiomer rotates in a clockwise direction, the other rotates it in the same amount but in anticlockwise direction

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4
Q

What happens when a molecule has more than chiral centre?

A

It will have more than two optical isomers

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5
Q

what aldehydes and ketones?

A

they are carbonyl compunds. they contain the
functional group C=O. aldehydes have their group at the end of the chain whilst ketones have theirs in the middle of the chain.

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6
Q

what do aldehydes and ketones reduce to?

A
  • aldehydes reduce to a primary alcohol

- ketones reduce to a secondary alcohol

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7
Q

what is the reducing agent for aldehydes and ketones?

A
  • normally NaBH4 (sodium tetrahydriborate III) or sodium borohydride dissolved in water in methanol
  • it has H- hydride ions, which has a lone pair of electrons. its a nucleophile which can attack the delta postive carbon on the aldehyde or ketones. (nucleophilic addition reaction)
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8
Q

what does hydrogen cyanide react with?

A

with carbonyl compounds to produce hydroxynitriles (CN+OH), its a nucleophilic addition reaction. hydrogen cyanide is a weak acid- it partially dissociates in water to form H+ and CN- ions.

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9
Q

describe the process of hydrogen cyanide with a carbonyl compound?

A

1 - the cyanide ion CN-, attacks the slightly +ve carbon atom and donates a pair of electrons to it. both electrons from the double bond transfer to the oxygen.
2- H+ from HCN or H2O bonds to the oxygen to form the OH group

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10
Q

what happens when brady’s reagent is dissolved in methanol and conc H2SO4?

A
  • it will react with carbonyl groups to form a bright orange precipitate. this only happens with c=o groups, the orange ppt is a derative of the carbonyl compound.
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11
Q

what does each different compound produce?

A
  • produces a crystalline derative melting point so if you measure the melting point of the crystals and compare it against known values you can identify
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12
Q

what is tollens reagent?

A

it can be used to distinguish between an aldehyde or ketone, it uses the fact that an aldehyde can be oxidised to a carboxylic acid, but a ketone cant. the reagent is colourless solution of silver nitrate dissolved in aq ammonia.

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13
Q

what happens when tollens reagent is used?

A
  • when they’re heated together in a test tube, the aldehyde is oxidised and the silver ions in the reagent are reduced to silver causing a silver mirror to form.
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14
Q

what are carboxylic acids?

A
  • they contain the group COOH, which is always found at the endof the molecule. they are weak acids so they partially dissociate in water to form carboxylate ions and H+ ions
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15
Q

why can carboxylic acids do as they’re polar molecules?

A
  • hydrogen bonds form between the highly polarised H+ atom and O- atoms on other molecules. this makes small carboxylic acids very soluble in water - they form H bonds with H2O
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16
Q

how do carboxylic acids react with metals?

A

carboxylic acids + metal -> salt + hydrogen

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17
Q

how do carboxylic acids react with carbonates?

A

carboxylic acids + carbonates -> salt + carbon dioxide + water

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18
Q

how do carboxylic acids react with metal oxides and alkali?

A

carboxylic acid + metal oxide/alkali -> salt + water

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19
Q

what are acyl or acid chlorides?

A

they have the group - COCl, and their general formula is CnH2nOCl. their names end in -oyl chlorides

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20
Q

how are acyl chlorides made?

A

they’re made by reacting carboxylic acids with SOCl2 (thionyl chloride), the OH group is replaced by Cl

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21
Q

how do acyl chlorides react with water?

A
  • they produce a carboxylic acid and HCl
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22
Q

how do acyl chlorides react with alcohols?

A
  • they produce a ester and HCl
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23
Q

how do acyl chlorides react with ammonia?

A
  • they produce a primary aide
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24
Q

how do acyl chlorides react with amines?

A
  • they produce a secondary amide
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25
Q

what happens in each of the acyl chloride reactions?

A
  • each time Cl is substituted by an oxygen or nitrogen group and hydrogen cyanide, they’re nucleophilic addition-elimination reactions
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26
Q

what is an ester?

A

its made by reacting an alcohol, with a carboxylic acid or carboxylic acid derative. the name is made up of alcohol and carboxylic acid

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27
Q

what happens when you heat a carboxylic acid?

A

if you heat a carboxylic acid with an alcohol in the presence of and acid catalyst, you get an ester, in a process called esterification. the catalyst used is concentrated sulfuric acid.

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28
Q

what do you have to do as the reaction between a carboxylic acid and alcohol is reversible?

A
  • you have to separate out the product as its formed. for small esters, you can warm the mixture and just distil off the ester, as its more volatile than other compounds.
  • larger esters are harder to form so its best to heat them under reflux and use fractional distillation to separate the ester.
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29
Q

how is a acid anydride made?

A

its made from to carboxylic acid molecules. acid anhydrides can be reacted with alcohols to make esters and carboxylic acid.
1 - the acid anhydride is warmed with alcohol no catalyst is needed
2- the products are an ester and a carboxylic acid which can be separated by distillation

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30
Q

how do acyl chlorides react with alcohols?

A

they react to form an ester and hydrogen chloride gas

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31
Q

what does acid hydrolysis do?

A

it splits the ester into a carboxylic acid and an alcohol. you have to reflux the ester with a dilute acid, such a HCL and H2SO4

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32
Q

what does base hydrolysis do?

A

you have to reflux the ester with a dilute alkali, such as NaOH you get a carboxylate salt and an alcohol

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33
Q

what is benzene?

A

it has the formula C6H6. it has a cyclic structure, with its six carbons joined together in a ring

34
Q

what did Kekule propose in 1865?`

A

he proposed that benzene was made up of a planar (flat) ring of carbon atoms, with alternating single and double bonds between them. each carbon is also bonded to one hydrogen atom
- he later adapted the model to say that the benzene molecule was constantly flipping between two isomers by switching over the double and single bonds

35
Q

if the kekule model was correct what does would it mean?

A

you’d expect there always to be three bonds with the length of a carbon single bond and three bonds with the length of a carbon double bond.

36
Q

what did x-ray diffraction show?

A

x-ray diffraction studies have shown that the carbon bonds in benzene have the same length ie they are between the length of a single bond and double bond
- so the kekule structure isnt right

37
Q

what does the delocalised model say?

A
  • that the p-orbitals of all six carbons atoms overlap to create a pi system. the system is made up of two-ring shaped clouds of electrons - one above and one below the plane of the six carbons
38
Q

what are the bonds like in the delocalised model?

A
  • all the bonds in the ring are the same length because all the bonds are the same. the electrons in the rings are said to be delocalised because they don’t belong to a specific carbon atom. they are represented as a circle inside the ring of carbons.
39
Q

what are compounds that contain a benzene ring called and give examples?

A

they’re called arenes or ‘aromatic compunds’

  • with cl its called chlorobenzene
  • with NO2 its nitrobenzene
  • with methyls its 1,3 dimethylbenzene
  • with OH its phenol
  • with NH2 its phenylamine
40
Q

describe electrophilic substitution of benzene?

A

results in a hydrogen atom being substituted by an electrophile. the mechanism has two steps - addition of the electrophile to form a positively charged intermediate, followed by loss of H+ from the carbon atom attached to the electrophile. the reforms the delocalised ring.

41
Q

what does a halogen carrier do?

A

it accepts a lone pair of electrons from a halogen atom on an electrophile. as the lone pair of electrons is pulled away, the polarisation in the molecule increases and sometimes a carbocation forms which makes the electrophile stronger
- the carriers include aluminium halides, iron halides and iron

42
Q

how does benzene react with halogens?

A

it reacts in the presence of an aluminium chloride catalyst, AlCl3. the catalyst polarises the halogen, allowing one of the halogen atoms to act as an electrophile. during the reaction, a halogen atom is substituted in place of a H atom, in halogenation

43
Q

what is freidal crafts alkylation?

A

it puts any alkyl group onto a benzene ring using a haloalkane, halogen carrier AlCl3 and reflux
- C6H6 + R-X -> C6H5R + HX

44
Q

what is freidal crafts acylation?

A

it substitutes an acyl group for an H atom on benzene. benzene is refluxed with an acyl chloride which produces phenylketones using AlCl3 and refluc

45
Q

how do you get a nitrobenzene? (Nitration)

A

when you warm benzene with concentrated nitric acid and concentrated sulfuric acid, you get nitrobenzene. sulfuric acid is a catalyst, it helps make the nitronium ion, NO2+ which is the electrophile. its then regenerated at the end of the reaction. At 50 degrees

46
Q

what are phenols?

A

they have the formula C6H5OH. the -OH group means that phenol is more likely to undergo electrophilic substitutions than benzene.

47
Q

what happens to the lone pairs in phenol during electrophilic substitution?

A

one of the lone pairs in a p-orbital of the oxygen atom overlaps with the delocalised ring of electrons in the benzene ring. the lone pair of electrons from the oxygen is partially delocalised into the pi-system. this increases the electron density making it more likely to be attacked by electrophiles.

48
Q

what can a functional group do to phenol?

A

it can change the electron density at certain carbon atoms making it more or less likely to react

49
Q

what are electron donating groups?

A

they include -OH and -NH2. they have electrons in orbitals that overlap with the delocalised ring and increase the electron density at carbons 2,4 and 6, so electrophiles are more likely to react at these positions.

50
Q

what are electron withdrawing groups?

A

they include -NO2. it doesn’t have any orbitals thatv can overlap with the delocalised ring and its electronegative, so it withdraws electron density from the ring.
- it withdraws electron density at carbons 2,4 and 6 so electrophiles are unlikely at these points. this has the effects of directing electrophilic substitution to the -3 and -5 positions.

51
Q

how does phenol react bromine water?

A

it reacts with bromine to decolourise it. the -OH group is electron donating so directs substitution to carbons 2,4 and 6. the product is 2,4,6-tribromophenol which is insoluble in water and precipitates out of water

52
Q

how does phenol react with dilute nitric acid?

A

it reacts to give two isomers of nitrophenol and water. nitrating phenol is easier than nitrating benzene which requires a conc nitric acid and conc H2SO4 catalyst. the difference is due to the activating effect of the OH group, which explains why you’re most likely to get NO2 at carbons 2&4.

53
Q

describe phenol’s reaction with NaOH solution?

A

phenol is weakly acidic, so will undego acid-base reactions. it reacts with NaOH solution at room temperature in a neutralisation reaction to form sodium phenoxide and water.

54
Q

how do you get an amine?

A

if one or more of the hydrogens in ammonia is replaced with an organic group, you get an amine. they can be primary, secondary or tertiary depending on how many alkyl groups the nitrogen atom is bonded to

55
Q

why are amines bases?

A

there’s a lone pair of electrons on the nitrogen atom of an amine that’s able to accept protons (H+ ions), this means amines are bases. they are neutralised by acids to make ammonium salts

56
Q

how are amines made?

A

they are made by heating a haloalkane with an excess ethanolic ammonia. you get a mixture of primary, secondary and tertiary amines and quaternary salts, as more than one hydrogen is likely to be substituted.

57
Q

what are amides?

A

they contain the functional group -CONH2. the carbonyl group pulls electrons away from the rest of the -CONH2 group, so amides behave differently from amines. you get primary or secondary amides depending on how many carbon atoms the nitrogen is bonded to

58
Q

what is an amino acid?

A

amino acids have the basic amino group (NH2) and an acidic carbonyl group (COOH). in an amino acid, both groups are attached to the same carbon atom. the general formula is RCH(NH2)COOH.

59
Q

what can COOH group in an amino acid group do?

A

it can react with an alkali to form a conjugate base - RCH(NH2)COO-. this combines with a positive ion to form a salt.
- it can react with an alcohol with a conc catalyst to form an ester

60
Q

how do amino acids react with acids?

A

they react to form a salt of the conjugate acid

RCH(NH2)COOH + HCl -> R(N+H3Cl-)COOH

61
Q

what are polymers?

A

polymers are long chain molecules formed when lots of small molecules called monomers join.

62
Q

what are addition polymers?

A

they are when the double bonds open up and molecules join to make long chains

63
Q

what are condensation polymers?

A

they are normally formed when two types of monomers join, each of which has at least two different functional groups. the functional group on one monomer reacts with a group on the other type of monomer to form a link.

64
Q

what is lost in condensation polymerisation?

A

each time a link is formed, a small molecule of water is lost

65
Q

where do bonds form in polyesters?

A

an ester link -COO is formed between two monomers

66
Q

where do bonds form in polyamides?

A

an amide link -CONH is formed between monomers

67
Q

how can condensation polymerisation be reversed?

A

by hydrolysis, water molecules are added back in and the links are broken. the reaction is done with an acid of base as hydrolysis with water is too slow

68
Q

how do polyamides hydrolyse?

A

they hydrolyse easier with an acid than a base

69
Q

how do polyesters hydrolyse?

A

they hydrolyse easier with a base. a metal salt of the carboxylic acid is formed

70
Q

how do you form a polyamide?

A

the carboxyl COOH group reacts with amino NH2 groups to form amide CONH links. a water molecule is lost each time an amide link is formed in a condensation reaction.

71
Q

how is a polyester formed?

A

carboxyl COOH group react with hydroxyl OH groups to form ester links COO in a condensation reactions.

72
Q

what do dicarboxylic acids and diamines have?

A

they have functional groups at the end of each molecule so both ends can react and lomg chains can form

73
Q

what happens in compounds where one of the COOH groups is swapped for an acyl chloride?

A

it will also react to form polyesters and polyamids. instead of water, HCL acid is eliminated in the condensation reaction

74
Q

How do you get from nitrobenzene to phenylamine?

A
  • Nitrobenzene is reduced to phenylammonium ions using a mixture of tin and concentrated hydrochloric acid. The mixture is heated under reflux
  • add NaOH
75
Q

what evidence disproved kekules model?

A
  • benzene doesnt undergo electrophilic addition reactions
  • benzene doesn’t decolourise bromine under normal conditions
  • bond length from x-ray diffraction showed it was between length of double and single bond
  • enthalpy of hydrogenation was less than expected
76
Q

what is the equation for the formation of the catalyst in the nitration of benzene?

A

HNO3 + H2SO4 -> NO2+ + HSO4- + H2O

- H+ + HSO4- -> H2SO4

77
Q

how can nitriles be formed from haloalkanes?

A

the nitrile group CN can be formed by reacting haloalkanes with sodium cyanide NaCN or KCN in ethanol. in this reaction the length of the carbon chain increases

78
Q

how nitriles be formed from aldehydes and ketones?

A

they will react with hydrogen cyanide in a nucleophilic addition reaction, and forms a carbon-carbon bond and therefore increases the length of the carbon chain

79
Q

how can nitriles be reduced?

A

they can be reduced to amines by reacting with hydrogen in the presence of a nickel catalyst.
- so the CN group becomes a NH2 group

80
Q

how can nitriles be hydrolysed?

A

nitriles undergo hydrolysis to form carboxylic acids by heating with dilute aqueous acid eg HCl
- the CN group gets replaces by COOH and NH -something form

81
Q

what two things can you get when you nitrate phenol?

A

using HNO3 in nitration you can get 2-nitrophenol or 4-nitrophenol

A-level Chemistry (5 decks)

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