6.1 Flashcards
(114 cards)
1
Q
what state is benzene at rtp
A
liquid
2
Q
what kind of hydrocarbons contain a benzene ring
A
aromatic
3
Q
whats benzenes reactivity
A
very stable and resistant to substitution and addition
4
Q
limitations of kekules model of benzene
A
benzene is a perfect hexagon, kekules model had double and single bonds, which are different lengths (double shorter)
less reactive than expected with the double bonds in kekules model (eg electrophilic sub needs a catalyst)
hydrogenation is much less exothermic than expected
5
Q
who created a model of benzene taht was wrong
A
kekule
6
Q
what is benzenes actual structure called
A
delocalised electron structure
7
Q
how is benzene bonded
A
p orbitals overlap to form pi bonds in a ring of delocalised pi electrons above and below the plane of the molecule
8
Q
how is benzene drawn skeletally
A
hexagon with a circle in it
9
Q
what is an arene
A
aromatic compounds that contain a benzene ring as part of their structure
10
Q
what is benzene molecular formula
A
C6H6
11
Q
which electrons are delocalised in benzene
A
the outer electron form the p orbital of each carbon atom
12
Q
what feature of benzene makes it stable
A
delocalised ring structure
13
Q
what was kekules model of benzene
A
cyclohexane with three double bonds
14
Q
why doesn’t benzene undergo electrophillic addition
A
because that would break up the stable delocalised ring of electrons
15
Q
why is benzene susceptible to attack from electrophiles
A
the ring is an area of high electron density
16
Q
explain electrophillic substitution
A
electrophile attacks, arrow from ring to electrophile
unstable intermediate is formed, draw H and electrophile both attacked to one of the carbons and a disrupted ring with a plus in the middle, with the opening facing the carbon with the electrophile and an arrow from the C-H bond to the ring through the gap
then draw benzene with the electrophile attached and draw H+ off on its own
17
Q
what does localised mean
A
an electron/pair that is associated with a specific atom/s
18
Q
what is delocalised
A
electrons that are not associated with specific a atom/s
19
Q
what is planar structure
A
a molecule where all of its atoms lie in the same plane
20
Q
what’s the use of a catalyst in the halogenation of benzene
A
it generates the electrophile
21
Q
what type of catalyst do you need in halogenation of benzene
A
a halogen carrier
22
Q
give examples of halogen carriers and the equations for the electrophile being generated and catalyst regeneration
A
AlCl3 or FeCl3
eg:
Cl2 + FeCl3 —> FeCl4^- + Cl^+
FeCl4^- + H^+ —> FeCl3 + HCl
23
Q
what is the electrophile in the halogenation of benzene
A
the halogen +
eg Cl^+
24
Q
what are the reagents in the halogenation of benzene
A
halogen and halogen carrier
25
what are the reagents in the halogenation of benzene
halogen and halogen carrier
26
what are the conditions for the halogenation of benzene
reflux
27
what is the electrophile for the nitration of benzene
NO^2+
28
what are the reagents in the nitration of benzene
conc nitric acid and conc sulphuric acid
29
what is the catalyst in the nitration of benzene
conc sulphuric acid
30
what are the equations showing the nitration of benzene including the regeneration of the catalyst
HNO3 + H2SO4 —> NO2^+ + HSO4^- +H2O
C6H6 + NO2^+ —> C6H5NO2 + H^+
HSO4^- + H^+ —> H2SO4
31
what are the conditions of the nitration of benzene and why
reflux at 55°C (to prevent further substitution of another NO2)
32
what are the reagents for friedel-crafts alkylation
haloalkane and anhydrous aluminium chloride (AlCl3)
33
what are the conditions for the alkylation of benzene
room temperature
34
what is the electrophile in the alkylation of benzene
a carbocation alkyl group eg: CH3+ or C2H5+
35
what are the reactions for the formation and regeneration for the catalyst in alkylation of benzene
CH3Cl + AlCl3 —> AlCl4^- + CH3^+
AlCl4^- + H+ —> AlCl3 + HCl
36
why is alkylation so important
increases the number of carbon atoms in a compound by forming carbon-carbon bonds
37
what are the reagents for acylation of benzene
an acyl chloride (R-COCl) and anhydrous aluminium chloride (AlCl3)
38
what’s re the conditions for acylation of benzene
reflux at 50°C
39
what are the conditions for acylation of benzene
reflux at 50°C
40
what’s the electrophile in the acylation of benzene
RC+O (eg: CH3C^+O)
so basically the acyl chloride with the chlorine removed
41
what are the equations for the use and regeneration for the catalyst in acylation of benzene
CH3COCl + AlCl3 —> AlCl4^- + CH3CO^+
AlCl4^- + H^+ —> AlCl3 + HCl
42
what is made form the acylation of benzene
a phenylketone
43
what happens when you put benzene in bromine water
nothing because the delocalised model of benzene makes it stable and not reactive enough to decolourise bromine water
44
what type of acids are phenols
weak but stronger than aliphatic alcohols because the O is more attracted to the benzene so it’s easier to lose the H+
45
why is phenol more reactive than benzene
the lone pair of electrons on the oxygen are delocalised into the benzene ring structure (electron donating group) which increases the electron density of the ring so less stable and more susceptible to electrophile attack and attack from weaker electrophile (can also induce dipoles in non polar molecules)
46
what do you need for the nitration of phenol
dilute nitric acid and no catalyst
47
what affect does the NO2 group have on electrons
electron withdrawing group
48
how does phenol react with NaOH
forms a soluble salt and water
49
how does phenol react with sodium
forms an ionic salt and hydrogen gas
50
what’s the difference between an aromatic alcohol and phenol
in phenol the OH group is attacked directly to the benzene ring nog an alkyl group attacked to the benzene
51
how does the oxygen in phenol react with the benzene ring
the p orbital on the O overlaps with the p orbitals in the ring
52
wh
53
where are reactions most likely to take place if there’s an electron donating group
2,4,6 because they are the most electron dense positions
54
which groups are electron donating
NH2 CH3 (alkyls) OH
55
what’s the effect of an electron withdrawing group
reduce the electron density of the aromatic ring and therefore reduces reactivity
56
what positions are most likely to react when there’s an electron withdrawing group
3,5
57
examples of electron withdrawing groups
NO2 CN CHO COOH
58
why are carbonyls soluble in water
they can form hydrogen bonds with water
59
why can’t carbonyls hydrogen bond to each other
they don’t have a delta positive hydrogen (bonded to F O N)
60
what are aldehydes
they have a carbonyl group on a carbon atom at the end of the carbon chain ( only attached to one other carbon)
61
what are ketones
have a carbonyl group on a carbon atom that is attached to two other carbon atoms
62
how to show oxidating and reducing agents in a reaction
[O] and [H]
63
how to make aldehydes
distil a primary alcohol
64
how to make ketones
reflux secondary alcohols
65
what is the colour change of potassium dichromate when an alcohol is oxided
orange to green
66
how do you turn a carbonyl back into an alcohol
reduce it via nucleophilic addition with NaBH4
67
where do nucleophiles attack carbonyls
the delta positive carbon centre
68
how does a nucleophilic reaction get drawn
arrow from nucleophiles lone pair or negative charge to the delta positive carbon, arrow from the double bond to the delta negative oxygen
attach nucleophile where it attacked, oxygen now has three lone pairs and is negative, arrow from one lone pair to and H+
new product formed with nucleophile on one bit and OH where the O was
69
what are the reagents for the addition of HCN to a carbonyl
refluxed with KCN and NaCN both need to be acidified to get the H+ needed
70
why do you use acidified KCN instead of just HCN when adding HCN
because HCN is very toxic and is a weak acid that struggles dissociating into its ions (KCN is ionic so produces more of CN- nucleophile)
71
what is the nucleophile in the nucleophilic addition of HCN to a carbonyl
CN- (has a triple bond)
72
what does the addition of HCN to a carbonyl make
hydroxynitriles
73
what’s the difference of the CN- attacking the carbonyl from above or below the planar double bond C=O
creates two different optical isomers becuase they are chiral carbons so they are different enantiomers
74
what is the nucleophile when reacting a carbonyl with NaBH4
H:-
75
how can you test for carbonyls
add 2,4-DNPH
a yellow orange or reddish orange precipitate will form if it is a carbonyl
76
why is the melting point of carbonyls useful
becuase they have sharp melting points so the melt over a narrow range of temperatures so you can determine what they are
77
how do you recrystallise
dissolve in minimum amount of hot water
cool to allow crystals to form and filter under reduced pressure
leave to dry
78
how do you recrystallise
dissolve in minimum amount of hot water
cool to allow crystals to form and filter under reduced pressure
leave to dry
79
what test can identify aldehydes from ketones and how
tollens reagent (a layer of silver will form on the walls of the test tube) it will remain colourless if it’s a ketone
it works because it oxidises the aldehyde to a carboxylic acid and reduces silver ions to silver
80
what are optical isomers
molecules that are non-superimposable mirror images of each other. they have the same chemical properties but interact with polarised light differently
81
what are the conditions needed for the addition of NaBH4 to a carbonyl
aqueous or alcoholic solution
82
how many reducing agents are needed in the addition of NaBH4 to a carbonyl
2
83
what happens to aldehydes and ketones in the addition of NaBH4 to a carbonyl
aldehydes reduced to primary alcohols
ketones reduced to secondary alcohols
84
what happens to boiling point of carboxylic acids as chain length increases
increases as more london forces
85
how is boiling point affected for straight chain isomers of carboxylic acids
it increases because there’s more surface contact
86
why are carboxylic acids soluble
because they can hydrogen bond
87
whats it called when carboxylic acids hydrogen bond with eachother twice
dimerisation
88
what happens to solubility as chain length increases
it decreases as the longer chain obscures the functional group whcih is the big that can dissolve
89
name and explain two derivatives of carboxylic acids (COOH)
acyl chlorides (COCl) the OH group is &replaced by a chlorine
acid anhydrides (two carboxylic acids joined together by their OH groups just with one O, so one H2O is removed)
90
carboxylic acids are strong enough acids to…
literature CO2 from carbonates (fizz)
91
reagent of chlorination of carboxylic acids
thionyl chloride (SOCl2) and dry conditions
92
what does the chlorination of a carboxylic acids make
an acyl chloride, SO2 (or other reagent leftovers) and HCl
93
how do you name acyl chlorides
take of the -ic from the carboxylic acid and replace with -yl chloride
eg ethanoyl chloride from ethanoic acid
94
what reactions do acyl chlorides undergo
nucleophilic addition-elimination reactions (basically nucleophilic substitution)
95
what does acyl chloride and water make
carboxylic acid
96
what does acyl chloride and alcohols make
esters
97
what does acyl chloride and ammonia make
amide
98
what does acyl chloride and amines make
N-substituted amide
99
how are esters named
alcohol-yl carboxylic acid-anoate
100
what are the reagents and conditions of esterification
carboxylic acids and alcohols refluxed with strong acid catalyst (usually conc sulphuric acid)
101
what does esterification make and where does it come from
makes H2O, one H from the alcohol, the OH from the carboxylic acid
102
why would you use an acid anhydride in esterification over an acyl chloride and what reaction are both of these
addition elimination mechanism
becuase it doesn’t produce toxic HCl as a side product
but the reaction is slower
103
what are the conditions for esterification using an acyl chloride
and what’s it’s by product
reflux under dry conditions
HCl gas
104
what are the conditions for esterification using an acid anhydride
and what’s it’s by product
reflux under dry conditions
a carboxylic acid
105
how does the hydrolysis of esters link with esterification
it’s the opposite reaction (splitting up an ester by adding water)
106
what happens if an ester and water react with hot aqueous acids
makes parent alcohol and carboxylic acid
107
what happens if an ester and water react with hot aqueous alkali
what’s the process called
makes a carboxylate salt (with the metal of the base often Na) and an alcohol (doesn’t react with the base becuase alcohols are weak acids and only react with concentrated bases)
process is called saponification
108
why do acyl chlorides react so violently
due to the very polar COCl group
109
how do you name benzene if it has a group attached that is more reactive
use it as the prefix phenyl
110
what groups are more reactive than benzene and why
OH (lone pairs)
NH2 (lone pairs)
CH=CH2 (alkenes because of the double bond)
111
Why is a double bond more susceptible to electrophilic attack than a benzene ring
Because in a double bond the pi electrons are localised, and in a benzene ring the pi ring is delocalised. So a double bond has a higher electron density so is more susceptible to electrophilic attack
112
Why is phenol more susceptible to electrophilic attack than benzene
(In phenol) Because the O partially donates a lone pair of electrons into the delocalised electron ring
So phenol’s ring is more electron dense than benzenes
So more susceptible to electrophilic attack
113
How can you check the purity of a solid
Find its melting point, compare to data book values. A pure solid should have a sharp melting point close to data book value.
114
Halogen carrier for bromination of benzene?
FeBr3
