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A-Level Chemistry > All Year 2 Organic > Flashcards

All Year 2 Organic Flashcards

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1
Q

what does NMR stand for?

A

nuclear magnetic resonance

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2
Q

13C NMR gives simpler spectra than 1H NMR

A

.

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3
Q

what mass number is needed for NMR

A

odd mass number

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4
Q

what solvents can the sample be dissolved in in 13C NMR & why?

A

polar solvents dissolve polar molecules & non-polar solvents dissolve non-polar molecules

CCl4 - non-polar molecule

D = 2H = even mass # so will not give signal
CDCl3 - polar molecule
C6D6

these C will give a signal but the value is known so is removed from the spectrum

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5
Q

what substance is used to calibrate the spectrum, what is its structure?

A

tetramethylsilane
Si(CH3)3 - see booklet

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6
Q

why is TMS used for calibration of spectrum?

A

it only gives one signal
it is non-toxic
it is inert
it has a low bp so can be easily removed from sample afterwards
it gives a signal that is far right than most signals from organic compounds - this is given the value of 0ppm

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7
Q

in 13C NMR, what is the # of signals based on?

A

the number of C atoms in different chemical environments

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8
Q

in 13C NMR, what does chemical shift depend on?

A

what other atoms/groups are near the C
the closer the C is to electronegative atoms (e.g. O, Cl), the greater the chemical shift
the more electronegative atoms near to the C, the greater the chemical shift

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9
Q

what is the relevance of the vertical axis in 13C NMR

A

it has no relevance

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10
Q

when looking at the table of 13C NMR values,

A

start at the bottom & work your way up

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11
Q

what is the relevance of the vertical axis in 1H NMR

A

it shows the intensity of the absorption

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12
Q

in 1H NMR, what is the number of signals based on?

A

there is one signal for each set of equivalent H atoms (H atoms in equivalent chemical environment)

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13
Q

in 1H NMR, what is the area of each signal based on?

A

the area of each signal is proportional to the # of equivalent H atoms (H atoms in equivalent chemical environment)

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14
Q

in 1H NMR, what is the integration ratio?

A

it indicates the relative numbers of H atoms in different environments/equivalent H atoms

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15
Q

for splitting patterns, the number of lines =

A

1 + the number of inequivalent H atoms on adjacent C atoms

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16
Q

across which atoms is there no splitting?

A

O
-OH group in alcohols rarely causes splitting or is split itself
sometimes the H of the OH appears as a broad bump

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17
Q

what are the relative heights of peaks in splitting?

A

singlet
doublet 1:1
triplet 1:2:1
quartet 1:3:3:1
multiplet

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18
Q

what is the number of neighbouring inequivalent H atoms for each signal?

A

singlet: 0
doublet: 1
triplet: 2
quartet: 3

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19
Q

name the 3 types of chromatography

A
  1. thin-layer chromatography
  2. column chromatography
  3. gas chromatography
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20
Q

describe thin-layer chromatography

A

a plate is coated with a solid & a solvent moves up the plate

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21
Q

describe column chromatography

A

a column is packed with a solid and a solvent moves down the column

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22
Q

describe gas chromatography

A

a column is packed with a solid or a solid coated by a liquid
a gas is passed through the column under pressure at high temp.

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23
Q

in chromatography, what does separation depend on

A

the balance b/w solubility in/affinity for the moving phase & retention by the stationary phase

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24
Q

how to calculate Rf value

A

distance travelled by component / distance travelled by solvent

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25
Q

what is retention time?

A

time taken for each substance to drain our of the column in column chromatography

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26
Q

the greater the affinity of a molecule to the mobile phase,

A

the shorter the distance it moves with the mobile phase

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27
Q

describe the method for thin-layer chromatography

A

metal plate coated with thin layer of powdered silica
pencil start line is drawn
solvent moves up the plate
sealed system to reduce loss of solvent & increase speed
can calculate Rf value
insoluble components stay on pencil line

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28
Q

describe the method for 2d TLC

A

after the first attempt, rotate the plate 90degrees & use a different solvent
this works well for substances that are insoluble in the first solvent

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29
Q

describe the method for column chromatography

A

vertical column is filled with a solid, powdered substance usually silica (to increase sa) = stationary phase
solvent that contains the mixture being analysed is added & moves down the column as the mobile phase
the different affinities of molecules in the mixture = they drain out of the column at different times & are collected as separate samples

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30
Q

silica is polar

A
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31
Q

describe the method for gas chromatography

A

thin tube is filled with a solid, powdered substance = stationary phase e.g. silica
inert gas carrier = mobile phase @ high pressure & high temp.
separate mixtures of volatile liquids
@ end of column, detectors identify each component & retention time for each compound can be recorded

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32
Q

describe gas chromatography mass spectrometry (GCMS)

A

type of GC
separated components are ionised as they emerge from column
identity & abundance of each component are measured by MS
GCMS is much faster & more accurate

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33
Q

what is the order of priority of functional groups?

A

alkenes
haloalkanes
amines
alcohols
ketones
aldehydes
nitriles
amides
acyl chloride
acid anhydride
esters
carboxylic acids

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34
Q

define optical isomerism

A

a form of stereoisomerism that occurs in molecules with a single chiral carbon centre

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35
Q

what is a chiral carbon atom?

A

C with 4 different groups attached
asymmetric

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36
Q

what are enantiomers?

A

2 compounds that are optical isomers

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37
Q

what are optical isomers?

A

molecules that are non-super imposable mirror images, and have different effects on the plane of polarised light
they have the same chemical & physical properties

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38
Q

what is a racemate/racemic mixture?

A

a 50/50 mixture of the enantiomers

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39
Q

what effect do optical isomers have on the plane of polarised light?

A

optical isomers can rotate the plane of polarised light

one enantiomer rotates the plane of polarised light in one direction & the other enantiomer rotates the plane of polarised light by the same amount in the opposite direction

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40
Q

what effect does a racemic mixture have on the plane of polarised light & why?

A

no effect - they are optically inactive
each enantiomer rotates the plane of polarised light by the same amount in opposite directions, so their effects cancel out

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41
Q

can ketones be oxidised?

A

no

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42
Q

what are the oxidation equations for:
primary alcohols
aldehydes
secondary alcohols?

A

see booklet

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43
Q

what are the reduction equations for aldehydes & ketones & what is the reducing agent?

A

see booklet
NaBH4 provides H- ions

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44
Q

what ion does reduction of aldehydes & ketones produce?

A

H-

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45
Q

describe the importance of acidified potassium dichromate (K2Cr2O7 & H2SO4)

A

orange Cr2O7 2- ion are reduced to green Cr3+ ions as they oxidise alcohol/aldehyde

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46
Q

under what conditions is a primary alcohol oxidised to an aldehyde & carboxylic acid?

A

aldehyde: distillation
carboxylic acid: reflux

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47
Q

what are the tests for an aldehyde?

A

Tollen’s reagent
Ag(NH3)2 + ions reduced to silver mirror
aldehyde is oxidised to carboxylic acid

Fehling’s solution
blue solution forms red precipitate
Cu2+ ions reduced to Cu2O
aldehyde is oxidised to carboxylic acid

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48
Q

what mechanism is involved in reduction?

A

nucleophilic addition

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49
Q

what are the reagent, conditions, products & overall equation of nucleophilic addition for reduction?

A

reagent: NaBH4 or LiAlH4
conditions: aqueous or LiAlH4 in ether (any H2O will explode)
products: from aldehydes, 1 alcohols & from ketones, 2 alcohols
overall equation: + 2[H] - see booklet

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50
Q

what is the mechanism for nucleophilic addition for reduction?

A

see booklet

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51
Q

what are the sources of H- & H+ ions in nuc. add. for reduction?

A

H- ions: NaBH4
H+ ions: water

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52
Q

what are the reagents, conditions, products & overall equation of nucleophilic addition for addition of HCN?

A

reagents: KCN followed by dilute strong acid
KCN is ionic & soluble so strong acid provides H+
conditions: aqueous
products: 2-hydroxynitriles
overall equation: + HCN - see booklet

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53
Q

what are the hazards of using KCN?

A

it is very toxic

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54
Q

why is HCN not the reagent for nuc. add.?

A

HCN is weak acid so v. low conc. so slow rate
HCN <–> H+ + CN-

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55
Q

what is the mechanism for nucleophilic addition for addition of HCN?

A

see booklet

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56
Q

what type of mixture is generally formed from nucleophilic addition for addition of HCN & why?

A

a racemic mixture
the CN- attacks (attaches to) the planar >C=O from above & below with equal probability so forms a 50/50 mixture of enantiomers (optical isomers)
so the product has no effect on the plane of polarised light

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57
Q

what is the effect of 2-hydroxymethylpropanenitrile on the plane of polarised light?

A

no effect on the plane of polarised light because there is no chiral carbon so not optically active

58
Q

what type of acids are carboxylic acids?

A

weak acids - only a small fraction of the molecules dissociate to release H+ ions in water

59
Q

what do carboxylic acids react with & what is the rate of reaction compared to strong acids?
what stays the same?

A

alkalis, metals, carbonates, ammonia
slower rate
moles that react are the same

60
Q

how do you name & draw the salts of carboxylic acids?

A

e.g. sodium methanoate
take off the H, leaving O-
& put +ve ion next to it with a + sign

61
Q

what is esterification?

A

making esters from carboxylic acids reacting with alcohols

62
Q

describe the reaction for esterification

A

slow & reversible
conc. acid catalyst

63
Q

what 3 things are needed for esterification?

A

alcohol
carboxylic acid
conc. acid

64
Q

what is the better method of esterification & what are the benefits?

A

reacting an alcohol & an acid anhydride
reaction is faster & give higher yield

65
Q

how are acid anhydrides formed?

A

from 2 carboxylic acids
-H on one & -OH on other are removed & form water
functional group for acid anhydrides: -C=O - O - C=O -

66
Q

describe ester hydrolysis in acidic conditions

A

esters can be broken down into carboxylic acid & alcohol
slow & reversible reaction

67
Q

describe ester hydrolysis in alkali conditions

A

= saponification
reaction goes to completion
forms salt of carboxylic acid & alcohol

68
Q

what are the uses of esters?

A
  1. food flavouring
  2. perfumes (contain mixtures of esters in solvents that quickly evaporate)
  3. used as solvents
  4. used as plasticisers, which are added to polymers to make them more flexible
69
Q

what are lipids?

A

esters
3 long carboxylic acids (fatty acids)
joined through propane-1,2,3-triol (glycerol), which has 3 alcohol groups

70
Q

what are oils & what do they contain?

A

lipids that are liquid at room temp.
tend to contain unsaturated fatty acids

71
Q

what are fats & what do they contain?

A

lipids that are solid at room temp.
tend to contain saturated fatty acids

72
Q

define saturated fatty acid

A

fatty acid with no C=C

73
Q

monounsaturated vs polyunsaturated fatty acids

A

mono: contain one C=C
poly: contain more than one C=C

74
Q

what is saponification?

A

lipids break down in alkali conditions (in KOH) to form the salts of fatty acids (anionic surfactants = soaps) + glycerol

75
Q

what is the reagent for the breakdown of lipids into fatty acids + glycerol?

A

HCl

76
Q

describe biodiesel production

A

lipid breaks down into 3 fatty acids & glycerol by reaction with KOH
fatty acids converted into methyl esters using methanol
KOH is a catalyst

77
Q

what type of fuel can biodiesel be?

A

carbon neutral
renewable

78
Q

define carbon neutral

A

no net annual release of CO2 into the atmosphere
bc same amount CO2 released when fuel is burned as the crops it was made from absorbed for PS

79
Q

define biofuel

A

fuel that gives out heat energy made from plants/organic matter

80
Q

how do soaps work?

A

fatty acid - hydrophobic
forms VDW forces b/w other long chain alkyl groups

C=O - O-
hydrophilic
O- surrounded by delta + H of water = ionic interaction

81
Q

compare acylation using carboxylic acids, acid anhydrides & acyl chlorides

A

carboxylic acids: slow, low yield

acid anhydride: acceptable rate & yield
cheaper
produce a carboxylic acid as a product

acyl chloride: high yield but too vigorous so cannot control reaction
much more expensive
produce corrosive HCl product

82
Q

what is acylation?

A

the insertion of an acyl group

83
Q

what is an acyl group?

A

r-c=o

84
Q

what are the reagents, conditions & products of nucleophilic addition-elimination for acylation?

A

acid anhydride or acyl chloride

from water - carboxylic acid
from alcohols - ester
from ammonia - amide
from amines - n-substituted amide

other product is an acid

85
Q

what atoms do the acyl group replace on alcohols & water?

A

H on the O of alcohols/water is replaced by an acyl group

86
Q

what atoms do acyl groups replace for amine/ammonia?

A

H on the N of an amine/ammonia is replaced by an acyl group

87
Q

acylation: with amines/ammonia, what does the acid by-product react with & form?

A

acid reacts with second molecule of amine/ammonia to form ammonium salt
the acid by-product donates H+ to another molecule of ammonia/amine

88
Q

what is the mechanism for acylation of ammines/ammonia & alcohols/water with acyl chlorides?

A

see booklet

89
Q

what is the structure of benzene?

A

C6H6
hexagonal ring with 1 H bonded to each C
planar
each C forms 3 covalent bonds
all C-C same length - intermediate b/w single & double bond

90
Q

how are the e-s arranged in benzene molecule?

A

one e- on each C atom in p orbital that is perpendicular to plane of the benzene ring
cloud of -ve charge above & below the plane of the ring = spare e-s overlap in pi cloud
ring of delocalised p e-s

91
Q

what are the 3 pieces of evidence for the delocalised structure of benzene compared with 1,3,5-cyclohexatriene?

A
  1. C-C bond length
  2. addition reactions
  3. enthalpy of hydrogenation
92
Q

how does C-C bond length give evidence for the delocalised structure of benzene?

A

in benzene, all 6 C-C bonds are the same length, intermediate b/w single & double bonds (0.139nm)

in 1,3,5-cyclohexatriene, there are 3 longer C-C bonds 0.154nm & 3 shorter C=C bonds 0.134nm

93
Q

how do addition reactions give evidence for the delocalised structure of benzene?

A

benzene reacts very slowly & needs a catalyst
so substitution reactions occur in preference to addition

1,3,5-cyclohexatriene readily undergoes electrophilic addition
bromine water turns from orange to colourless

94
Q

how does enthalpy of hydrogenation give evidence for the delocalised structure of benzene?

A

cyclohexene + H2 –> cyclohexane enthalpy change = -120kJ
1,3,5-cyclohexatriene + 3H2 –> cyclohexane -360kJ
but hydrogenating benzene:
benzene + 3H2 –> cyclohexane -208kJ

–> benzene is more stable than 1,3,5-cyclohexatriene
benzene is 152kJ more stable than the triene
bc benzene has delocalised e-s
the 152kJ = delocalisation energy of the p e-s

95
Q

what is the stability of cyclohexane?

A

most energetically stable compared w benzene & triene

96
Q

how do aromatics react?

A

electrophilic substitution

97
Q

what are the reagents, conditions & products of electrophilic substitution for nitration?

A

conc. HNO3 & conc. H2SO4
below 50C to minimise multiple substitutions
products: aromatic nitro compounds

98
Q

what are aromatic nitro compounds used for?

A

to make aromatic amines –> azo dyes
to make explosives

99
Q

what is the overall equation for electrophilic substitution (nitration)?

A

see booklet

100
Q

what is the equation for making the electrophile in nitration (NO2+)?

A

HNO3 + H2SO4 –> NO2+ + HSO4- + H2O

101
Q

what is the mechanism for electrophilic substitution (nitration)?

A

see booklet
at end show regeneration of catalyst: H+ + HSO4- –> H2SO4

102
Q

what are the reagents, conditions & products of electrophilic substitution for Friedel-Crafts acylation?

A

acyl chloride & AlCl3
<50C, anhydrous to prevent reaction of AlCl3
products: aromatic ketones –> organic synthesis

103
Q

what is the overall equation for electrophilic substitution (F-C acylation)?

A

see booklet

104
Q

what is the equation for making the electrophile in F-C acylation?

A

see booklet

105
Q

what is the mechanism for electrophilic substitution (F-C acylation)?

A

see booklet
at end show regeneration of catalyst: H+ + AlCl4- –> AlCl3 + HCl

106
Q

compare Friedel-Crafts acylation with normal acylation

A

see table in booklet

107
Q

be aware of F-C acylation with acid anhydrides - never come up before

A

see booklet

108
Q

what are the different types of amines?

A

primary, secondary, tertiary
related to ammonia (NH3)
aromatic amines: N is directly bonded to the benzene ring

109
Q

what are the interactions b/w amine molecules?

A

some hydrogen bonding but weaker than in alcohols
no H bonding b/w tertiary amines

110
Q

compare the melting points of primary, secondary & tertiary amines & quaternary ammonium salts

A

primary & secondary: both have H bonding (&VDW) b/w molecules
secondary amine has higher mp bc larger so stronger VDW

tertiary: lowest mp bc no H bonding b/w molecules - only VDW b/w molecules

quaternary ammonium salt: highest mp - ionic interactions –> lattice

111
Q

describe the structure of quaternary ammonium salts

A

no lone pair of e-s on N so do not behave like amines/ammonia
one dative covalent bond - N donates 2e-s

112
Q

describe the preparation of aliphatic amines by reacting NH3 + halogenoalkanes

A

excess conc. NH3 in ethanol, high pressure in sealed container
equation: R-X + 2NH3 –> R-NH2 + NH4X
nucleophilic substitution mechanism
if conc. of halogenoalkane > conc. of NH3, further substitutions happen to form 2 & 3 amines then 4 ammonium salt.
if excess conc. NH3 used, 1y amine main product (but still mixture of products)
if excess halogenoalkane is used, 4y ammonium salt is main product

113
Q

describe the preparation of aliphatic amines by reduction of nitrile compounds

A

only one amine formed, not a mixture
product has one more C atom than the starting material
1. formation of a nitrile from a halogenoalkane
2. reduction of the nitrile to form an amine

114
Q

describe the formation of a nitrile from a halogenoalkane

A

R-X + KCN warm ethanol & water –> R-CN +KX
H2O dissolves ionic KCN
ethanol dissolves halogenoalkane

115
Q

describe the reduction of the nitrile to form an amine

A

R-CN + 2H2 Ni catalyst & heat –> R-CH2-NH2

or R-CN + 4[H] LiAlH4 in ethoxyethane –> R-CH2-NH2

116
Q

describe the preparation of 1y aromatic amines & equation
what would the product be if NaOH not added?

A

reduction of nitro compounds
tin & moderately conc. HCl followed by NaOH
see booklet for equation

4y ammonium salt - see booklet

117
Q

how are amines Bronsted-Lowry bases?
Lewis bases?

A

proton acceptors
weak bases
bases bc lone pair of e-s on N atom can readily accept a proton
equilibrium reaction see booklet

e- pair donor

118
Q

what does the ability of ammonia/amine to act as a base depend on?

A

how well the lone pair on N can accept H+
the higher the e- density of the lone pair on N, the better it can accept H+ –> so the stronger the base

119
Q

what is the order of base strength?

A

3y amine > 2y amine > 1y amine > NH3 > aromatic amine

120
Q

compare & explain the difference in base strength of 3y, 2y & 1y amines to ammonia

A

the more alkyl groups that are substituted onto the N atom,
the more electron density is pushed onto the lone pair on N
so the it is better at accepting H+
so the stronger the base

121
Q

compare & explain the difference in base strength of ammonia & aromatic amines

A

the lone pair on N is delocalised into the benzene ring,
so it is less electron dense
so worse H+ acceptor
so weaker base

122
Q

describe the successive nucleophilic substitution reactions of amines = further substitution

A

the amine product has a greater e- density on the lone pair on N so is better at reacting with the halogenoalkane than the original molecule
the H atoms on N are successively replaced by the R group from the halogenoalkanes to eventually form the quaternary ammonium salt

123
Q

draw mechanism for formation of aliphatic amines

A

nuc. sub.
see booklet

124
Q

describe the uses of quaternary ammonium salts

A

cationic surfactants
fabric softener
hair conditioner

ionic ‘head’ = hydrophilic
alkyl chain ‘tail’ = hydrophobic

125
Q

state the equation & draw the mechanism for acylation of amines

A

nuc. addition-elimination
see booklet

replaces H on N with acyl group –> amide + HCl or carboxylic acid
2nd molecule reacts with HCl/carb. acid –> salt

126
Q

what is the general structure of amino acids?

A

H2N-C-H-R-COOH
amine group, carboxylic acid group & variable R group
every amino acid exists as a Zwitterion
(20 naturally occurring AAs)

127
Q

define Zwitterion

A

each amin group is protonated by a carboxylic acid group on another molecule

128
Q

what attractions are there b/w Zwitterions?

A

ionic attraction

129
Q

describe how amino acids show optical isomerism

A

amino acids (except glycine) have a chiral C atom with 4 different groups attached to it
so when the plane of polarised light is shone at them, it is rotated
only one of these enantiomers is present in nature

130
Q

define primary structure of an amino acid

A

the sequence of amino acid units in the chain

131
Q

define secondary structure of an amino acid

A

the chain of AAs is often arranged in a helix (or B-pleated sheets) = 2y structure
helix is held together by hydrogen bonds b/w C=O & H-N in adjacent spirals
there are many H bonds –> stable

132
Q

define tertiary structure of an amino acid

A

the helix of AAs is folded into a specific 3D shape = 3y structure
caused by bonds b/w R groups: electrostatic/ionic interactions, H-bonds, disulfide bridges (& permanent dipole-dipole)

133
Q

how does the amine group of an AA react?

A

protonated by acids
acylation with acyl chlorides & acid anhydrides
nucleophilic substitution with halogenoalkanes

134
Q

how does the carboxylic acid group of an AA react?

A

deprotonated by bases
esterification with alcohols (with conc. acid catalyst)

135
Q

how are peptides formed?

A

amino acids are joined together in condensation reactions to make dipeptides & polypeptides
- joined together by amide/peptide

136
Q

draw diagram of dipeptide

A

2 forms
C=O-N-H in middle

137
Q

how are peptides/proteins broken down?

A

hydrolysed into their constituent AAs
either with:
strong acid –> -NH3+
strong alkali –> -COO-

138
Q

draw the structure of amino acids in alkali, neutral & acidic conditions

A

neutral = Zwitterion
see table in booklet

139
Q

state how you can differentiate b/w stereoisomers of amino acids

A

optical isomerism
shine plane of polarised light at sample then observe which way it is rotated
each enantiomer will rotate it in opposite directions by the same amount

140
Q

why is a polyester biodegradable?

A

is can be easily hydrolysed

A-Level Chemistry (14 decks)

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