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

Topic 6- Organic chemistry and Analysis Flashcards

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
reducing an aldehyde
reduced to primary alcohols NaBH4 (reducing agent) aldehyde + 2[H] forms an alcohol
26
reducing a ketone
reduced to secondary alcohols NaBH4(reducing agent) ketone +[H] forms an alcohol
27
reactions of carbonyl compounds with HCN
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
28
testing for carbonyls
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
29
solubility of carboxylic acids
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
what is a derivative of carboxylic acid?
a compound that can be hydrolysed to form the parent carboxylic acid esters acyl chlorides acid anhydrides amides
31
esters
named after the parent carboxylic acid from which it’s derived ends in -oate
32
acyl chlorides
named after the parent carboxylic acid it is derived from ends in -oyl chloride
33
acid anhydrides
formed by the removal of water from two carboxylic acid molecules
34
esterfication
alcohol + carboxylic acid forms an ester small amount of concentrated sulfuric acid acts as a catalyst
35
acid hydrolysis of esters
the reverse of esterfication ester heated under reflux with dilute aqueous acid acid acts as a catalyst forms alcohol and carboxylic acid
36
alkaline hydrolysis of esters
ester heated under reflux with aqueous hydroxide ions forms carboxylate ion and alcohol
37
preparation of acyl chlorides
formed from their parent carboxylic acid and SOCl2 forms acyl chloride, SO2 and HCl
38
reaction of acyl chloride with alcohol
forms an ester and HCl
39
reaction of acyl chlorides with phenols
forms ester and HCl
40
reaction of acyl chloride with water
violent reaction forms carboxylic acid and HCl
41
reaction of acyl chlorides with ammonia
ammonia acts as nucleophile forms primary amide and ammonium chloride
42
reaction of acyl chloride with a primary amine
forms secondary amide
43
reactions of acid anhydrides
reacts similarly to acyl chloride
44
amines
organic compounds derived from ammonia in which one or more hydrogens have been replaced
45
aliphatic amine
nitrogen attached to at least one straight or branched carbon chain
46
aromatic amine
nitrogen attached to an aromatic ring
47
classifying amines
primary- RNH2 secondary- (R)2NH tertiary- (R)3N
48
naming amines
add -amine onto the end of the name of the alkyl chain or it can begin with amino if not a primary amine
49
amines as bases
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
preparation of aliphatic amines
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
preparation of aromatic amines
heat nitrobenzene under reflux with tin and concentrated HCl tin and HCl react to produce the reducing agent
52
heating under reflux
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
simple distillation
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
filter under reduced pressure
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
recrystallisation
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
using the measurement of melting point to check purity
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
test for alkene
add bromine water orange to colourless
58
test for haloalkane
add silver nitrate in ethanol warm in water bath chloroalkane- white bromoalkane- cream iodoalkane- yellow
59
test for phenols
add bromine water white precipitate
60
test for carboxylic acids
add sodium carbonate releases carbon dioxide bubble through limewater turns it cloudy
61
test for ketones and aldehydes
add 2,4-DNPH, sulfuric acid, water and methanol bright orange precipitate
62
test for aldehyde
add Tollens’ reagent silver mirror
63
tests for primary and secondary alcohols
add acidified potassium dichromate (VI) warm in water bath orange to green
64
thin layer chromatography
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
retention time
time taken from injection to detection
66
gas chromatography- separation by adsorption
component molecules bind to the surface of the solid stationary phase stronger adsorption= more component molecules are slowed down
67
gas chromatography- separation by relative solubility
components dissolve in the liquid stationary phase greater solubility in stationary phase= more component molecules slowed down
68
number of peaks in gas chromatography = ???
number of components in mixture
69
area under peak in gas chromatography = ???
relative amount of each component
70
identifying components using gas chromatography
compare retention time with known values
71
mixture and stationary phase have similar intermolecular forces
lots of interactions long retention time
72
mixture and stationary phase have different intermolecular forces
lack of interactions short retention time

OCR A level chemistry (6 decks)

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