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OCR A level chemistry > Topic 6- Organic chemistry and Analysis > Flashcards

Topic 6- Organic chemistry and Analysis Flashcards

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1
Q

What is benzene?

A

a colourless, sweet smelling, highly flammable liquid which contains a hexagonal ring of six carbon atoms

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2
Q

describe the kekulé model

A

suggested the structure of benzene was based on a six carbon ring joined by alternating single and double bonds

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3
Q

state the evidence to disprove the kekulé model

A

1) lack of reactivity- does not undergo electrophilic addition reactions and does not decolourise bromine meaning benzene cannot have any double bonds.
2) lengths of carbon to carbon bonds- single bonds are longer than double bonds however in benzene all the bonds are the same length.
3) hydrogenation enthalpies- enthalpy change of hydrogenation of benzene is predicted to be -360 but it is actually -208 which is about 150 less exothermic than expected

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4
Q

describe the delocalised model of benzene

A

~ six carbon atoms and six hydrogen atoms
~ each carbon contributes one electron to a delocalised electron ring above and below the plane
~ each p orbital over laps with adjacent p orbitals in such a way that delocalisation is extended over all six carbons
~ this is an example of a delocalised pi electron system

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5
Q

what is the name of the process when benzene reacts with an electrophile?

A

electrophilic substitution

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6
Q

nitration of benzene

A

benzene + nitric acid
catalysed by sulfuric acid
electrophilic substitution

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7
Q

halogenation of benzene

A

requires a halogen carrier= AlCl3, FeCl3 etc.
electrophilic substitution
bromination- bromine
chlorination- chlorine

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8
Q

alkylation reactions

A

substitution of hydrogen with alkyl group
benzene+ haloalkane
in presence of AlCl3 which acts as a halogen carrier

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9
Q

acylation reactions

A

benzene reacts with acyl chloride (RCOCl)in prescience of AlCl3 forming an aromatic ketone

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10
Q

comparison of benzene and cyclohexane

A

cyclohexane-
electrons localised
high electron density
susceptible to electrophilic attack

benzene-
electrons delocalised
low electron density
less susceptible to electrophilic attack

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11
Q

what is phenol?

A

organic compound containing an organic ring with an -OH attached
classed as weak acids but do not react with carbonate ions

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12
Q

why does phenol act as a weak acid?

A

less soluble in water than alcohol due to presence of the non-polar benzene ring
When dissolved in water it partially dissociates forming aether phenoxide ion and a proton

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13
Q

reaction of phenol with NaOH

A

forms the salt sodium phenoxide and water

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14
Q

bromination of phenol

A

phenol+bromine
forms 2,4,6-tribromophenol (white precipitate)
decolourises bromine water

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15
Q

nitration of phenol

A

phenol+dilute nitric acid
forms 2-nitro phenol and 4-nitro phenol

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16
Q

comparison of phenol and benzene

A

phenol is more reactive due to a lone pair of electrons from the p-orbital of the -OH group being donated into the pi-system
increases electron density
phenol more susceptible to electrophilic attack

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17
Q

activating and deactivating groups

A

activating groups- make the benzene ring react more readily with electrophiles
deactivating groups- make the benzene ring react less readily with electrophiles

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18
Q

2,4,6 directing groups

A

-NH2
-OH
-C6H5
-F, -Cl etc.
all activating groups

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19
Q

3,5 directing groups

A

-RCOR
-COOR
-COOH
-CN
-NO2
all deactivating groups

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20
Q

what are the 2 carbonyls?

A

aldehydes
ketones

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21
Q

aldehydes

A

carbonyl functional group found at end( carbon 1)
structural formula CHO
end in -al

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22
Q

ketones

A

carbonyl group attached to two carbons
structural formula CO
end in -one

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23
Q

oxidation of aldehydes

A

aldehyde+ oxidising agent forms carboxylic acid
under reflux with acidified potassium dichromate(VI)

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24
Q

is the c=o group in carbonyls polar or non-polar?

A

polar meaning aldehydes and ketones react with some nucleophiles(nucleophilic addition)

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25
Q

reducing an aldehyde

A

reduced to primary alcohols
NaBH4 (reducing agent)
aldehyde + 2[H] forms an alcohol

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26
Q

reducing a ketone

A

reduced to secondary alcohols
NaBH4(reducing agent)
ketone +[H] forms an alcohol

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27
Q

reactions of carbonyl compounds with HCN

A

HCN- colourless, extremely poisonous liquid
usually use KCN when completing this reaction in laboratories
forms a hydroxynitrle
remember to use notes to look at the mechanism

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28
Q

testing for carbonyls

A

brady’s reagent-
both aldehydes and ketones
forms an orange precipitate
tollens’ reagent-
tests for aldehydes
forms a silver mirror
Ag+ ions reduced as the aldehyde is oxidised

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29
Q

solubility of carboxylic acids

A

C=O and O-H bonds are polar
hydrogen bonds form with water molecules
carboxylic acids with up to 4 carbons are soluble in water

30
Q

what is a derivative of carboxylic acid?

A

a compound that can be hydrolysed to form the parent carboxylic acid
esters
acyl chlorides
acid anhydrides
amides

31
Q

esters

A

named after the parent carboxylic acid from which it’s derived
ends in -oate

32
Q

acyl chlorides

A

named after the parent carboxylic acid it is derived from
ends in -oyl chloride

33
Q

acid anhydrides

A

formed by the removal of water from two carboxylic
acid molecules

34
Q

esterfication

A

alcohol + carboxylic acid forms an ester
small amount of concentrated sulfuric acid acts as a catalyst

35
Q

acid hydrolysis of esters

A

the reverse of esterfication
ester heated under reflux with dilute aqueous acid
acid acts as a catalyst
forms alcohol and carboxylic acid

36
Q

alkaline hydrolysis of esters

A

ester heated under reflux with aqueous hydroxide ions
forms carboxylate ion and alcohol

37
Q

preparation of acyl chlorides

A

formed from their parent carboxylic acid and SOCl2
forms acyl chloride, SO2 and HCl

38
Q

reaction of acyl chloride with alcohol

A

forms an ester and HCl

39
Q

reaction of acyl chlorides with phenols

A

forms ester and HCl

40
Q

reaction of acyl chloride with water

A

violent reaction
forms carboxylic acid and HCl

41
Q

reaction of acyl chlorides with ammonia

A

ammonia acts as nucleophile
forms primary amide and ammonium chloride

42
Q

reaction of acyl chloride with a primary amine

A

forms secondary amide

43
Q

reactions of acid anhydrides

A

reacts similarly to acyl chloride

44
Q

amines

A

organic compounds derived from ammonia in which one or more hydrogens have been replaced

45
Q

aliphatic amine

A

nitrogen attached to at least one straight or branched carbon chain

46
Q

aromatic amine

A

nitrogen attached to an aromatic ring

47
Q

classifying amines

A

primary- RNH2
secondary- (R)2NH
tertiary- (R)3N

48
Q

naming amines

A

add -amine onto the end of the name of the alkyl chain
or it can begin with amino if not a primary amine

49
Q

amines as bases

A

behave as bases as the lone pair of electrons on the nitrogen can accept a proton
forms a dative covalent bond
neutralise acids to make salts

50
Q

preparation of aliphatic amines

A

heat haloalkane with an excess of ethanolic ammonia
nucleophilic substitution
the amine can also act as a nucleophile due to the lone pair of electrons

51
Q

preparation of aromatic amines

A

heat nitrobenzene under reflux with tin and concentrated HCl
tin and HCl react to produce the reducing agent

52
Q

heating under reflux

A

heating in a flask with reflux condenser prevents vapours escaping while the reaction is happening
vapours from the reaction mixture condense and flow back into the flask

53
Q

simple distillation

A

Simple distillation is used to separate 2 liquids with different boiling points
It can be used effectively to separate liquids that have a large difference in their boiling points

54
Q

filter under reduced pressure

A

solids are removed by filtration using a buchner or a hirsch funnel with suction from a water pump
buchner funnel- used for filtering large volumes
hirsch funnel- used for filtering small volumes

55
Q

recrystallisation

A

1) dissolved the impure solid in the minimum volume of hot solvent
2)cool filtrate so that the product recrystallises, leaving the smaller amounts of soluble impurities in solution
3)filter the cold solution under reduced pressure to recover the purified product
4)wash crystals with cold solvent

56
Q

using the measurement of melting point to check purity

A

use data book or an online database to look up the melting point
impure solids will have a lower melting point and melt over a temperature range

57
Q

test for alkene

A

add bromine water
orange to colourless

58
Q

test for haloalkane

A

add silver nitrate in ethanol
warm in water bath
chloroalkane- white
bromoalkane- cream
iodoalkane- yellow

59
Q

test for phenols

A

add bromine water
white precipitate

60
Q

test for carboxylic acids

A

add sodium carbonate
releases carbon dioxide
bubble through limewater
turns it cloudy

61
Q

test for ketones and aldehydes

A

add 2,4-DNPH, sulfuric acid, water and methanol
bright orange precipitate

62
Q

test for aldehyde

A

add Tollens’ reagent
silver mirror

63
Q

tests for primary and secondary alcohols

A

add acidified potassium dichromate (VI)
warm in water bath
orange to green

64
Q

thin layer chromatography

A

thin layer of aluminium oxide or silicon oxide supported on a plastic or glass plate
coloured compounds easy to see
colourless compounds made visible with ninhydrin, UV light or iodine crystals
components identified by comparing R.F value calculated to known values

65
Q

retention time

A

time taken from injection to detection

66
Q

gas chromatography- separation by adsorption

A

component molecules bind to the surface of the solid stationary phase
stronger adsorption= more component molecules are slowed down

67
Q

gas chromatography- separation by relative solubility

A

components dissolve in the liquid stationary phase
greater solubility in stationary phase= more component molecules slowed down

68
Q

number of peaks in gas chromatography = ???

A

number of components in mixture

69
Q

area under peak in gas chromatography = ???

A

relative amount of each component

70
Q

identifying components using gas chromatography

A

compare retention time with known values

71
Q

mixture and stationary phase have similar intermolecular forces

A

lots of interactions
long retention time

72
Q

mixture and stationary phase have different intermolecular forces

A

lack of interactions
short retention time

OCR A level chemistry (6 decks)

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