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chemistry 2 > organic 3 p2 > Flashcards

organic 3 p2 Flashcards

(103 cards)

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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 in benzene?

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 (combustion!)

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, 50*C
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
equation to form an electrophile that could be used to acylate benzene starting with AlCl3 and RCOCl
AlCl3 + RCOCl --> AlCl4 - + RCO+ RCO+ can attack benzene
26
what is happening when AlCl4 - is formed in terms of electrons?
the lone pair of electrons on the chlorine atom is forming a coordinate bond to Al
27
how is the AlCl3 catalyst reformed?
AlCl4 - + H+ --> HCl + AlCl3 (H+ from benzene)
28
how could you use a Friedel-Crafts mechanism to add a methyl group to a benzene ring?
use a haloalkane and AlCl3 to create an electrophile that can attack benzene
29
if you are considering cyclic compounds, what might happen if two double bonds are next to each other?
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
30
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?
makes the molecule more stable; makes enthalpy of hydrogenation more positive
31
what is the structure of phenol?
benzene with an OH group
32
phenol and bromine water reaction
phenol + 3Br2 --> 2,4,6-tribromophenol + 3HBr
33
what are the reasons for the relative ease of bromination (electrophilic) of phenol, compared to benzene?
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 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
34
what is the amine functional group?
RNH2 -amine or amino-
35
why are amines so reactive?
the lone pair of electrons on the Nitrogen - due to polar N-H bond
36
what shape are amines around the N? bond angle?
trigonal pyramidal 107* due to lone pair on N
37
what kind of intermolecular forces do they have? why?
hydrogen bonding due to polar N-H bond and lone pair of electrons on N atom
38
do amines have intermolecular forces which are stronger than or weaker than alcohols? why?
weaker, as N has a lower electronegativity than O --> weaker hydrogen bonding
39
which primary amines are soluble in water/alcohols? why?
up to 4 carbon atoms, as they can hydrogen bond to water molecules after this, non-polarity of hydrocarbon chain makes them insoluble
40
what kind of solvents are most other amines soluble in?
less or non-polar solvents
41
solubility of phenylamine? why?
not very soluble due to the non-polarity of the benzene ring - C6H5 cannot form bonds
42
how can amines act as bases?
when they bond with an H+ ion
43
how can amines act as nucleophiles?
when they bond with an electron-deficient C atom (donate lone pair from N)
44
what is the product from the basic action of an amine with water?
RNH3 + ammonium ion which forms a salt with an anion
45
how could you regenerate the soluble amine from the ammonium salt?
add a strong base (NaOH) --> removes H+ ions from ammonium ion
46
in order to be the strongest base, what must a particular amine have (out of a set of amines)?
greatest electron density around the N atom, making it a better electron pair donor (attracts protons more)
47
out of ammonia, primary aliphatic and primary aromatic amines what is the strongest base?
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
48
what positive/negative inductive effect mean?
positive inductive effect = donates electrons, increase density around N negative means remove electrons, decrease density around N
49
what effect do alkyl groups have (on electron density and base strength)
positive effect - increase electron density around N --> stronger base
50
what affect do aryl groups have (on electron density and base strength)?
negative inductive effect - decrease electron density around N --> weaker base
51
why are tertiary amines never good bases?
they are insoluble in water
52
place in order of base strength: NH3, primary amine, secondary amine, phenylamine
secondary amine > primary amine > NH3 > phenylamine
53
how can primary amines form secondary, tertiary amines and quarternary ammonium ions?
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
54
how would you maximise the yield of the primary amine from a haloalkane?
use excess ammonia
55
how do you get from a nitrile to a primary amine?
reduction using Ni/H catalyst H2, Ni, 200*C
56
why is nitrile to amine a purer method of synthesising amines?
only the primary amine can be formed
57
how do you form an ammonium chloride salt from nitrobenzene? what conditions are needed?
reduce the nitrile using Tin/HCl --> forms an ammonium salt with Cl- ions room temperature
58
nitrobenzene --> phenylamine equation
C6H5NO2 + 6[H] --> C6H5NH2 + 2H2O
59
what mechanism is used for forming amides from acyl chlorides and amines?
nucleophilic addition/elimination
60
methylamine and HCl equation
CH3NH2 + HCl --> CHNH3 + Cl-
61
ethylamine and bromoethane equation
2CH3CH2NH2 + CH3CH2Br --> CH3CH2NH2CH2CH3 + CH3CH2NH3Br
62
ethylamine and copper (II) ions equation
4CH3CH2NH2 + Cu(H2O)6 2+ ⇌ [Cu(CH3CH2NH2)4(H2O)2]2+ + 4H2O
63
how do you prepare amides from acyl chlorides?
use a primary amine and the condition is room temperature RCOCl + 2CH3NH2 --> RCONHCH3 + CH3NH3 +Cl
64
what is the linkage in a polyamide?
-(C=O)-(N-H)- O H = - -C-N-
65
which molecule is eliminated when a polyamide is formed?
H2O
66
what are the two monomers used to form a polyamide? examples of polyamides?
diamine and dicarboxylic acid Nylon, Kevlar
67
which monomers is nylon-6,6 made from?
1,6-diaminohexane and hexanedioic acid
68
which monomers is terylene made from?
benzene-1,4-dicarboxylic acid ethane-1,2-diol
69
what are the two functional groups of amino acids?
NH2 and COOH
70
how many naturally occurring amino acids are there in the body?
20
71
are α-amino acids chiral? why?
yes - one carbon has 4 different substituents except glycine where R = H
72
which enantiomer do α-amino acids exist as in nature?
- enantiomer L enantiomer
73
how can amino acids be synthesised industrially?
nucleophilic addition RCHO + NH4CN --> RCH(NH2)COOH + NH4Cl hydrolysis with dilute HCl (under reflux) RCH(NH2)CN + HCl + 2H2O --> RCH(NH2)COOH + NH4Cl
74
is the product from amino acids being synthesised naturally optically active? why?
no, a racemic mixture is formed 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
75
in what form do amino acids exist as solids? what consequences does this have?
zwitterions (ionic lattice) - high melting and boiling points
76
what colour solids are most zwitterions at room temperature?
white solids
77
do zwitterions dissolve in water? non-polar solvents? why?
yes - but not in non-polar solvents due to ionic nature/polar bonds
78
zwitterion
ions which have both a permanent positive and negative charge but are neutral overall
79
how do zwitterions occur in amino acids?
COOH is deprotonated --> COO- NH2 is protonated --> NH3+
80
what happens to amino acids in acidic conditions?
gains a proton on NH2 group
81
name of chains of up to 50 amino acids?
polypeptides
82
name of chain of more than 50 amino acids?
proteins
83
what are polypeptides and proteins found in?
enzymes, wool, hair, muscles
84
what is the process called by which polypeptides or proteins can be broken down into their constituent amino acids?
hydrolysis reflux for 24 hours and 6 mol dm-3 HCl
85
what is a TLC plate made of?
plastic sheet coated with silica SiO2 this is the stationary phase
86
describe how you would carry out Thin Layer Chromatography
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
87
why does TLC separate amino acids?
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
88
what do you often have to do to enable the amino acids to be seen on the chromatogram?
spray with ninhydrin (amino acids are colourless, ninhydrin turns their spots purple) or shine UV light on them
89
what would you observe in a melting point determination if the sample was not pure?
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
90
why might the melting point appear different to the true value?
temperature of the material in the machine might be different to the temperature shown on the thermometer - apparatus error
91
when purifying by recrystallisation, why is the minimum volume of hot solvent used?
so that a saturated solution is created, so that as many crystals will fall out of solution as possible when it is cooled
92
why is the solution filtered hot when purifying by recrystallisation?
to remove insoluble impurities and ensure that the crystals do not form in the filter paper
93
why is the solution cooled in an ice bath when purifying by recrystallisation?
to ensure as many crystals as possible fall out of solution - yield is higher
94
why are the crystals washed with cold water when purifying by recrystallisation?
to remove soluble impurities
95
how would you separate the crystals from the reaction mixture when purifying by recrystallisation?
filter under reduced pressure using a Buchner funnel
96
why might percentage yield be below 100% for recrystallisation?
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
97
in a distillation setup, why is it necessary to have a continuous water flow around the condenser?
so that the water remains cool in order for the mixture to be distilled
98
describe a method that can be used to separate immiscible liquids
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
99
examples of drying agents
magnesium sulphate calcium chloride
100
how are drying agents used?
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
101
what does re-distillation mean?
when a liquid is purified by using multiple distillations
102
how to prepare Grignard reagent?
a haloalkane is dissolved in dry ether and reacted with magnesium
103
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?
react grignard reagent with CO2 or with carbonyl compounds in dry ether

chemistry 2 (22 decks)

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