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chemistry 2 > organic 3 p2 > Flashcards

organic 3 p2 Flashcards

1
Q

what is benzene’s formula and structure?

A

C6H6
hexagon with a circle drawn inside
flat, regular hexagon, bond angle =120*

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2
Q

what is another name for arenes? why did this come about?

A

aromatic compounds, as first found in sweet-smelling dyes

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3
Q

what is the most common type of reaction of benzene?

A

substitution (of a H for a different functional group)

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4
Q

what is the bond length between adjacent C atoms?

A

intermediate between C-C and C=C

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5
Q

what happens to the 4th electron in the p orbital of each C atom in benzene?

A

it delocalises to form rings of electron density above and below the hexagon, forming rings of delocalised electron density above/below the hexagon

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6
Q

what is the effect on the stability of the rings of benzene on electron density?

A

makes benzene very stable, even though it is unsaturated (aromatic stability)

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7
Q

what is the thermochemical evidence that benzene is more stable than cyclohexa-1,3,5-triene?

A

hydrogenation of cyclohexane = -120kJmol-1
–> cyclohexa-1,3,5-triene = -360kJmol-1
benzene hydrogenation = -208kJmol-1 so benzene is 152kJmol-1 more stable

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8
Q

why is cyclohexa-1,3,5-triene not a suitable model for benzene?

A

would not be symmetrical (C=C shorter than C-C), but benzene is
would easily undergo addition reactions across the double bonds - benzene does not
would form two isomers on the addition of Br2 or similar - benzene does not

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9
Q

what is the appearance of benzene at 298K?

A

colourless liquid

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10
Q

why does benzene have a relatively high melting point?

A

close packing of flat hexagonal molecules when solid

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11
Q

is benzene soluble in water? why?

A

no - non polar

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12
Q

dangers of benzene?

A

it is a carcinogen

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13
Q

how do you name compounds containing a benzene ring?

A

-benzene or -phenyl
can designate position on ring using numbers if there is more than one substituent

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14
Q

why is benzene attacked by electrophiles?

A

high electron density above/below ring due to delocalised electrons

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15
Q

what is delocalisation energy and what is the effect of this on the reaction of benzene?

A

the large amount of energy that is needed to break the aromatic ring apart
results in the aromatic ring almost staying intact

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16
Q

what is seen when benzene is combusted? why?

A

smoky flames due to soot from unburnt carbon
this is because of the high Carbon:Hydrogen ratio

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17
Q

benzene and oxygen equation

A

C6H6(l) + 7.5O2 –> 6CO2 + 3H2O

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18
Q

which ion is used to nitrate benzene?

A

NO2+ (+charge is on the nitrogen)
nitronium ion or nitryl cation

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19
Q

how is NO2+ ion generated? (conditions and equations)

A

conc H2SO4 and conc HNO3
H2SO4 + HNO3 –> H2NO3+ + HSO4-
H2NO3+ –> H2O + NO2+
overall: H2SO4 + HNO3 –> HSO4- + NO2+ +H2O

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20
Q

how is the H2SO4 catalyst regenerated in the nitration of benzene?

A

HSO4 - + H+ –> H2SO4 (H+ from benzene ring)

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21
Q

what are the uses of nitrated arenes?

A

production of explosives e.g. TNT
(1-methyl-2,4,5-trinitritobenzene) - releases lots of heat and gas on explosion
to make aromatic amines that are used for industrial dyes

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22
Q

how do substituents with a positive inductive effect (e.g. alkyl groups) affect further substitution?

A

they release electrons into the delocalised electron ring, increasing the electron density and making further substitution reactions more likely/quick
direct substituents to the 2,4,6 positions

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23
Q

how do substituents with a negative inductive effect (e.g. NH2) affect further substitution?

A

remove electrons from the delocalised electron ring, decreasing the electron density and making further substitution reactions less likely/quick
direct substitutions to 3,5 positions

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24
Q

what type of catalyst is used for Friedel-Crafts reaction?

A

a halogen carrier (e.g. AlCl3)

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25
Q

equation to form an electrophile that could be used to acylate benzene starting with AlCl3 and RCOCl

A

AlCl3 + RCOCl –> AlCl4 - + RCO+
RCO+ can attack benzene

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26
Q

what is happening when AlCl4 - is formed in terms of electrons?

A

the lone pair of electrons on the chlorine atom is forming a coordinate bond to Al

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27
Q

how is the AlCl3 catalyst reformed?

A

AlCl4 - + H+ –> HCl + AlCl3 (H+ from benzene)

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28
Q

how could you use a Friedel-Crafts mechanism to add a methyl group to a benzene ring?

A

use a haloalkane and AlCl3 to create an electrophile that can attack benzene

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29
Q

if you are considering cyclic compounds, what might happen if two double bonds are next to each other?

A

C=C bonds are in close proximity, so electrons in pi cloud/p orbitals can partially delocalise and move between the two C=C double bonds

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30
Q

what effect would electrons in p orbitals moving between the two C=C double bonds have on the stability of the molecule and its enthalpy of hydrogenation?

A

makes the molecule more stable; makes enthalpy of hydrogenation more positive

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31
Q

what is the structure of phenol?

A

benzene with an OH group

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32
Q

phenol and bromine water reaction

A

phenol + 3Br2 –> 2,4,6-tribromophenol + 3HBr

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33
Q

what are the reasons for the relative ease of bromination of phenol, compared to benzene?

A

in a phenol the lone pair of electrons on the oxygen is partially delocalised into the ring and therefore activates the ring and increases electron density
therefore electrophiles are more attracted to phenol

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34
Q

what are the reasons for the relative ease of bromination of phenol, compared to benzene?

A

phenols are very weakly acidic even weaker acids than carboxylic acids
only carboxylic acids will react with sodium carbonate as a phenol is not strong enough an acid to react

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35
Q

what is the amine functional group?

A

RNH2
-amine or amino-

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36
Q

why are amines so reactive?

A

the lone pair of electrons on the Nitrogen - due to polar N-H bond

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37
Q

what shape are amines around the N? bond angle?

A

trigonal pyramidal 107* due to lone pair on N

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38
Q

what kind of intermolecular forces do they have? why?

A

hydrogen bonding due to polar N-H bond and lone pair of electrons on N atom

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39
Q

do amines have intermolecular forces which are stronger than or weaker than alcohols? why?

A

weaker, as N has a lower electronegativity than O –> weaker hydrogen bonding

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40
Q

which primary amines are soluble in water/alcohols? why?

A

up to 4 carbon atoms, as they can hydrogen bond to water molecules
after this, non-polarity of hydrocarbon chain makes them insoluble

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41
Q

what kind of solvents are most other amines soluble in?

A

less or non-polar solvents

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42
Q

solubility of phenylamine? why?

A

not very soluble due to the non-polarity of the benzene ring - C6H5 cannot form bonds

43
Q

how can amines act as bases?

A

when they bond with an H+ ion

44
Q

how can amines act as nucleophiles?

A

when they bond with an electron-deficient C atom (donate lone pair from N)

45
Q

what is the product from the basic action of an amine with water?

A

RNH3 + ammonium ion which forms a salt with an anion

46
Q

how could you regenerate the soluble amine from the ammonium salt?

A

add a strong base (NaOH) –> removes H+ ions from ammonium ion

47
Q

in order to be the strongest base, what must a particular amine have (out of a set of amines)?

A

greatest electron density around the N atom, making it a better electron pair donor (attracts protons more)

48
Q

out of ammonia, primary aliphatic and primary aromatic amines what is the strongest base?

A

primary aliphatic amines - strongest
aromatic amines - weakest
aromatic amine weakest bc the lone pair on the N is partially delocalised into the ring and therefore decreases the attraction of H+ ion
primary aliphatic amines are stronger bases than ammonia as the alkyl groups are electron releasing and push electrons towards the nitrogen atom and so make it a stronger base

49
Q

what positive/negative inductive effect mean?

A

positive inductive effect = donates electrons, increase density around N
negative means remove electrons, decrease density around N

50
Q

what effect do alkyl groups have (on electron density and base strength)

A

positive effect - increase electron density around N –> stronger base

51
Q

what affect do aryl groups have (on electron density and base strength)?

A

negative inductive effect - decrease electron density around N –> weaker base

52
Q

why are tertiary amines never good bases?

A

they are insoluble in water

53
Q

place in order of base strength: NH3, primary amine, secondary amine, phenylamine

A

secondary amine > primary amine > NH3 > phenylamine

54
Q

how can primary amines form secondary, tertiary amines and quarternary ammonium ions?

A

multiple substitutions; primary amine is a nucleophile that attacks the original haloalkane etc
problem: not efficient as low yield of primary amine due to multiple substitutions

55
Q

how would you maximise the yield of the primary amine?

A

use excess ammonia

56
Q

how do you get from a nitrile to a primary amine?

A

reduction using Ni/H catalyst

57
Q

why is this a purer method of synthesising amines?

A

only the primary amine can be formed

58
Q

how do you form an ammonium chloride salt from nitrobenzene? what conditions are needed?

A

reduce the nitrile using Tin/HCl –> forms an ammonium salt with Cl- ions
room temperature

59
Q

nitrobenzene –> phenylamine equation

A

C6H5NO2 + 6[H] –> C6H5NH2 + 2H2O

60
Q

what mechanism is used for forming amides from acyl chlorides and amines?

A

nucleophilic addition/elimination

61
Q

methylamine and HCl equation

A

CH3NH2 + HCl –> CHNH3 + Cl-

62
Q

ethylamine and bromoethane equation

A

2CH3CH2NH2 + CH3CH2Br –> CH3Ch2NH2CH2CH3 + CH3CH2NH3Br

63
Q

ethylamine and copper (II) ions equation

A

4CH3CH2NH2 + Cu(H2O)6 2+ ⇌ [Cu(CH3CH2NH2)4(H2O)2]2+ + 4H2O

64
Q

how do you prepare amines from acyl chlorides?

A

use a primary amine and the condition is room temperature
RCOCl + 2CH3NH2 –> RCONHCH3 + CH3NH3 +Cl

65
Q

what is the linkage in a polyamide?

A

-(C=O)-(N-H)-
O H
= -
-C-N-

66
Q

which molecule is eliminated when a polyamide is formed?

A

H2O

67
Q

what are the two monomers used to form a polyamide? examples of polyamides?

A

diamine and dicarboxylic acid

Nylon, Kevlar

68
Q

which monomers is nylon-6,6 made from?

A

1,6-diaminohexane and hexanedioic acid

69
Q

which monomers is terylene made from?

A

benzene-1,4-dicarboxylic acid
ethane-1,2-diol

70
Q

what are the two functional groups of amino acids?

A

NH2 and COOH

71
Q

how many naturally occurring amino acids are there in the body?

A

20

72
Q

are α-amino acids chiral? why?

A

yes - one carbon has 4 different substituents
except glycine where R = H

73
Q

which enantiomer do α-amino acids exist as in nature?

A
  • enantiomer
74
Q

how can amino acids be synthesised industrially?

A

nucleophilic addition
RCHO + NH4CN –> RCH(NH2)COOH + NH4Cl
hydrolysis with dilute HCl (under reflux)
RCH(NH2)CN + HCl + 2H2O –> RCH(NH2)COOH + NH4Cl

75
Q

is the product from amino acids being synthesised naturally optically active? why?

A

no, a recemic mixture is frmed as the CN- ion can attack from above or below the planar C=O bond with equal likelihood
an equal amount of each enantiomer is formed, so no net effect on plane polarised light

76
Q

in what form do amino acids exist as solids? what consequences does this have?

A

zwitterions (ionic lattice) - high melting and boiling points

77
Q

what colour solids are most zwitterions at room temperature?

A

white solids

78
Q

do zwitterions dissolve in water? non-polar solvents? why?

A

yes - but not in non-polar solvents due to ionic nature/polar bonds

79
Q

zwitterion

A

ions which have both a permanent positive and negative charge but are neutral overall

80
Q

how do zwitterions occur in amino acids?

A

COOH is deprotonated –> COO-
NH2 is protonated –> NH3+

81
Q

what happens to amino acids in acidic conditions?

A

gains a proton on NH2 group

82
Q

name of chains of up to 50 amino acids?

A

polypeptides

83
Q

name of chain of more than 50 amino acids?

A

proteins

84
Q

what are polypeptides and proteins found in?

A

enzymes, wool, hair, muscles

85
Q

what is the process called by which polypeptides or proteins can be broken down into their constituent amino acids?

A

hydrolysis
reflux for 24 hours and 6 mol dm-3 HCl

86
Q

what is a TLC plate made of?

A

plastic sheet coated with silica SiO2
this is the stationary phase

87
Q

describe how you would carry out Thin Layer Chromatography

A

spot the samples onto a pencil line a few cms above the base of the TLC plate
place in a beaker with solvent level below the pencil line
ensure there is a lid on the beaker to keep the inside saturated with solvent vapour
wait until the solvent front is almost at the top of the TLC plate; then remove from the beaker and analyse

88
Q

why does TLC separate amino acids?

A

solvent carries amino acids up the TLC plate
the rate of movement depends on the balance between that amino acid’s affinity for the solvent and affinity for the stationary phase

89
Q

what do you often have to do to enable the amino acids to be seen on the chromatogram?

A

spray with ninhydrin (amino acids are colourless, ninhydrin turns their spots purple)
or shine UV light on them

90
Q

what would you observe in a melting point determination if the sample was not pure?

A

sample melts over a large range (more than 3*C)
sample’s melting point is below the accepted value due to impurities disrupting the structure

91
Q

why might the melting point appear different to the true value?

A

temperature of the material in the machine might be different to the temperature shown on the thermometer - apparatus error

92
Q

when purifying by recrystallisation, why is the minimum volume of hot solvent used?

A

so that a saturated solution is created, so that as many crystals will fall out of solution as possible when it is cooled

93
Q

why is the solution filtered hot when purifying by recrystallisation?

A

to remove insoluble impurities and ensure that the crystals do not form in the filter paper

94
Q

why is the solution cooled in an ice bath when purifying by recrystallisation?

A

to ensure as many crystals as possible fall out of solution - yield is higher

95
Q

why are the crystals washed with cold water when purifying by recrystallisation?

A

to remove soluble impurities

96
Q

how would you separate the crystals from the reaction mixture when purifying by recrystallisation?

A

filter under reduced pressure using a Buchner funnel

97
Q

why might percentage yield be below 100%?

A

product lost during filtration, drying and weighting - not all transferred from one piece of apparatus to the other
product is left dissolved in the solution - some does not crystallise, some left on filter paper, sample still wet

98
Q

in a distillation setup, why is it necessary to have a continuous water flow around the condenser?

A

so that the water remains cool in order for the mixture to be distilled

99
Q

describe a method that can be used to separate immiscible liquids

A

pour the mixture into a separating funnel and some distilled water
add the stopper and invert the flask to mix
equalise the pressure by opening the stopper as required
continue shaking until there is no ‘whistle’ sound
to collect the water in the lower layer, open the stopper and place a beaker under the spout
use another beaker to collect the desired organic layer
shake the liquid with some drying agent

100
Q

examples of drying agents

A

magnesium sulphate
calcium chloride

101
Q

how are drying agents used?

A

add a selected drying agent to the organic product
if the drying agent forms clumps add some more until they are moving freely
use gravity filtration to collect the dry product
filtrate is the product

102
Q

what does re-distillation mean?

A

when a liquid is purified by using multiple distillations

103
Q

how to prepare Grignard reagent?

A

a haloalkane is dissolved in dry ether and reacted with magnesium

104
Q

what are the two ways to increase the length of the carbon chain in a molecule by the use of magnesium to form grignard reagents?

A

react grignard reagent with CO2 or with carbonyl compounds in dry ether

chemistry 2 (21 decks)

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