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Theory Flashcards

(117 cards)

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1
Q

Why chain isomers have different physical properties

A

Shape of molecule has changed

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2
Q

Do positional isomers have different chemical and physical properties

A

Yes

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3
Q

Do fg isomers have different chemical and physical properties

A

Yes

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4
Q

What shape is alkane molecules and why

A

Tetrahedral (109.5)
4 bonded pairs
All repel equally

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5
Q

What force is between alkane molecules

A

Induced dipole dipole

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6
Q

Why does propane have a high boiling point than methane

A

Propane is longer
So has stronger induced dipole dipole forces
Because it has more surface contact and more electrons to interact
So takes more energy to overcome

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7
Q

Why does a branched chain have a lower bp than a straight alkane

A

Branched chains can’t pack as closely together
And have smaller molecular surface areas
So weaker induced dipole dipole forces
So less Energy needed to overcome

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8
Q

Why do liquid alkanes need to be vaporised before combustion

A

Only happens in gaseous states

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9
Q

What type of alkanes are more volatile

A

Small

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10
Q

Why are long alkanes good fuels

A

Have lots of bonds to break

So release lots of energy per mole

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11
Q

Why is CO toxic

A

Oxygen is carried by haemoglobin
CO is better at binding to haemoglobin than oxygen
So no oxygen is carried around the body
Leads to oxygen deprivation

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12
Q

What reaction type is used in free radicals

A

Free radical substitution

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13
Q

Write the reaction mechanism for free radical substitution

A

Cl2 -> 2Cl🖤

Cl🖤 + CH4-> CH3🖤 + HCl
CH3🖤 + Cl2 -> CH3Cl + Cl🖤

Cl🖤 + CH3🖤 -> CH3Cl

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14
Q

What is the 2 problems with free radical substitution

A

You get a mixture of products that need to be filtered

And the substitutions can happen anywhere along the alkane chain

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15
Q

How to stop a mixture of products in free radical substitution

A

Having excess alkane

So the free radical is more likely to react with that Than a chloromethane molecule

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16
Q

Why are alkenes more reactive that alkanes

A

Alkenes contain a pi and sigma bond
The double bond contains 4 electrons = high electron density
Pi bond sticks out from the rest of the molecule
Attracts electrophiles
Pi bond has low bond enthalpy so doesn’t take much energy to overcome

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17
Q

Why are alkanes unreactive

A

Only contain sigma bonds
High bond enthalpy = take a lot of energy to overcome
Non polar = dont attract electrophiles or nucleophiles

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18
Q

Why can’t double bonds rotate

A

Because of how the p orbitals overlap

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19
Q

What is the shape around Alkenes

A

Tribunal planar

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20
Q

Why can alkenes form stereoisomers

A

Due to lack of rotation from double bonds

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21
Q

What happens about naming stereoisomers when all the groups are different

A

Assign each group a priority on each C atom

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22
Q

What are e isomers also called

A

Trans

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23
Q

What are z isomers also called

A

Cis

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24
Q

When does the cis/trans naming system not work

A

When all groups are different

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25
What type of reaction do alkenes undergo
Electrophilic addition
26
How do you know what product will be the most stable in a unsymmetrical alkane when a hydrogen halide is being added
Carbon with the most alkyl groups is the most stable Feeds the most electrons into the carbon atom Forms a more stable carbocations
27
Why are small alcohols soluble in water
H bonds form between water and the OH group | Most of the chain is polar so it fully dissolves
28
Why are long alcohols not as soluble
Most of the chain isn’t polar so can’t h bond with the water
29
Why do alcohols have a low volatility
They can h bond between molecules | Takes lots of energy to overcome
30
Why do aldehydes have to be distilled off as soon as it’s formed
The aldehyde boils at a lower temp that the alcohol | So need to be distilled off fast before it oxidises too far into a carboxylic acid
31
What is the only way of oxidising a tertiary alcohol
Burning
32
What type of reaction is it when haloalkanes react with alkali
Nucleophilic substitution
33
Why do iodo alkanes get hydrolysed the fastest
They have the weakest bond (lowest bond enthalpy) so requires less energy to overcome
34
What are cfcs
Only contain carbon fluorine and chlorine | All h atoms have been replaced by halogens
35
How is ozone formed
O2 -> O+O (UV) | O2 + O -> O3
36
Why are cfcs bad
Catalyse break down of ozone Causing holes in ozone in atm Let in harmful Uv
37
Write the mechanism of cfcs destroying the ozone
CF2Cl2 -> 🖤CF2Cl + Cl🖤 Cl🖤 + O3 -> O2 + ClO🖤 ClO🖤 + O -> O2 + Cl🖤 Overall = O3 + O -> 2O2
38
Why are Cl🖤 so bad
They are regenerated So are a catalyst So 1 Cl🖤 destroys lots of ozone before it forms a stable compound
39
What other compound besides Cl🖤 destroys the ozone
NO🖤
40
Why is the kekule model incorrect
X ray diffraction = all carbon to carbon bonds are the same length, between the lengths of a single and double bond Enthalpy change of hydration = much less exothermic than expected at 208 instead of 360. Meaning the bonds are stronger than expected = more stable Doesn’t readily undergo electrophilic addition = bromination needs heat and UV light but cyclohexene does it at room temp.
41
What reaction does benzene undergo
Electrophilic substitution;
42
Why is a halogen carrier needed for reactions with benzene
The electrophile has to be strong to attack a benzene ring because it’s so stable The halogen carrier accepts a lone pair of electrons from the halogen atom of an electrophile . Polarising the electrophile making it more strongly attracted to the benzene ring
43
Draw the mechanisms for benzene + Br2
-
44
What reactants are needed for a friedel craft alkylation
Haloalkane AlCl3 Benzene
45
What reactants are needed for a friedel craft acylation
Acyl chloride Alcl3 Benzene
46
What is the catalyst used in the format of nitrobenzene
Conc H2SO4
47
What is the equation of the formation of the nitronium ion
Hno3 + H2SO4-> h2no3+ + hso4- | H2no3 -> no2+ + h2o
48
Why does the temp need to be kept below 55 for the nitration on benzene
To stop multiple substitutions which make a explosive substance
49
Draw the nitratation of benzene mechanism
-
50
Why is phenol more reactive than benzene
Contain OH group The O atom in a p orbital has electrons that overlap the delocalised electron ring The lone pair becomes partially delocalised into the pi system Increasing the electron density of the ring More likely to be attack by electrophiles
51
Why are some groups donating
They have electrons in orbitals which overlap into the tepee delocalised electron ring Increasing electron density at 2,4,6 Electrophiles more attracted to these positions
52
What are the electron donating groups
Nh2 oh EDG
53
Why are some groups withdrawing
Doesn’t have any electrons in orbitals that overlap with the delocalised electron ring Also electro negative So reduce electron density from the ring At 2,4,6 Most electron dense at 3,5 So electrophiles more attracted there
54
What is the product of bromine + phenol
2,4,6 tribromophenol
55
How do you know phenol has reacted with bromine
Forms precipitate in water Decolourises
56
What is the ph of phenol
3/4 | Weak acid
57
Why does phenol not react with sodium carbonate
Phenol isn’t a strong enough acid
58
What is used to reduce aldehydes and ketones back to alcohols
NaBH4 | Dissolved in water and methanol
59
What supplies the nucleophile in the reduction of ketones and aldehydes
H- from NaBH4 | It has a lone pair of electrons
60
What compound does HCN make with carbonyl compounds
Hydroxynitriles
61
What type of solution is HCN
Weak acid
62
What is the electrophile in the formation of hydroxynitrileS
CN-
63
What type of reaction is the reduction of ketones/aaldehydes
Nucleophyllic addition
64
What type of reaction is the formation of hydroxynitriles
Nucleophilic addition
65
What precautions are used in the lab when making a hydroxynitriles
Used acidified sodium cyanide instead of HCN because HCN is highly toxic Done in fume cupboards
66
Why are carboxylic acids soluble in water
Can h bond due to polar oh and o group
67
What is the fg of acyl chlorides
COCl
68
How are acyl chlorides made
Carboxylic acid + SOCl2
69
What happens when acyl chloride + water
Carboxylic acid + HCl Vigorous Cold
70
What happens when acyl chloride + alcohol
Ester + HCl Vigorous Room temp
71
What happens when acyl chloride + ammonia
Primary amide + HCl Violent Room temp
72
What happens when acyl chloride + amines
Secondary amide + HCl Violent Room temp
73
What products would u actually get in a lab when ammonia + ethanoyl chloride
Ethanamide HCl Ammonium chloride Because the HCl product reacts with the ammonia reactant
74
Which is the most effectuent way of making an ester
Alcohol + acyl chloride Faster And irreversible
75
What reaction type do acyl chlorides undergo
Nucleophilic addition elimination
76
What is the reaction between ethanoyl chloride + phenol
Phenyl ethanoate + HCl
77
Describe the formation of an ester from alcohol + carboxylic acid
Conc H2SO4 catalyst Reversible = need to separate product as it’s made by distillation or reflux Water produced
78
Describe estérification from alcohol and acid anhydride
No catalyst Separate by fractional distillation Ester + carboxylic acid produced
79
Describe base hydrolysis
Splits ester into carboxylic acid and aldohol Reflux Dilute acid Reversible reaction
80
How do u keep the postsotion of eqm to the right in acid hydrolysis
Add lots of water
81
Explain base hydrolysis
Reflux Dilute alkali (naoh) Forms carboxylate salt and alcohol
82
What is an amine
H replaced in NH3 by an organic group
83
What type of solution are amines
Basic
84
What are amines bases
There is a lone pair on NH3 | So it can accept a proton
85
What is the reaction with ethylamine + HCl
Ethylammonium chloride | Ch3Ch2NH3+Cl-
86
How do you make amines
Haloalkane + ethanolic ammonia
87
How do you separate primary secondary and tertiary amines
Fractional distillation
88
Why do you get a mixture of primary secondary and tertiary amines
More than one H is likely to be substituted on NH3
89
What is the reaction of ammonia + bromoethane
Ethylamine + NH4Br
90
How do you form diethylamine
Nh3 + ethylamine + bromoethane
91
How do you make aromatic amines
Reduce nitrobenzene Nitrobenzene + tin metal + conc HCl Reflux Add NaOH Makes phenyl amine + 2H2O
92
What are amides
Have the functional group conh2
93
Why do amides behave differently to amines
The carbonyl group on CONH2 pull electrons away from the Nh2
94
What is a secondary amide
One of the H is replaced by a methyl group
95
Amino acid + alkali
Forms salt + water
96
Amino acid + acid
Salt
97
Amino acid + alcohol
Ester + H2O | H2SO4 catalyst
98
What is a chiral center
Carbon atom with 4 different groups attached
99
What are optical isomers
Mirror images of each other Can’t be super imposed Optically active
100
What does optically active mean
They rotate the plane polarised light
101
What are polymers
Long chains of monomers joined together
102
Wh at are addition polymers
Double bond opens up
103
What is condensation polymerisation
Formed from 2 types of monomers Functional groups link Small molecules lost (H2O)
104
How are polymers broken down
Hydrolysis Water added back Done with acid abs base
105
What is acid hydrolysis
Add H+ | Forms dicarboxylic acid and diamine
106
What is base hydrolysis
Dicarbocylate acid salt | Diol
107
What is a CN-
A nucleophile
108
What will CN- react with
React with carbon centres With a partially positive charge Forming a new c -c bond Forms a nitrile
109
How to increase length of carbon chain by addicting cyanide
Add HCN to slightly positive carbon
110
What type of reaction is haloalkanes + cyanide
Nucleophilic subsituation
111
How to form nitrile but from haloalkane
Reflux haloalkane with KCN in ethanol | Using nuclephylic substitution
112
How do you form a hydroxynitriles
Aldehyde/ketone + HCN
113
Why are nitrile groups useful in synthesis
Very reactive so can be replaced by other fg
114
How to reduce a nitrile to a primary amine
LiAlH4 + Dilute acid Or Sodium metal + ethanol
115
What method is used to reduce nitriles in industry
Adding h gas and metal catalyst (Ni) at high Temp and pressure by catalytic hydrogenation
116
Why is catalytic hydrogenation used in industry
LiAlH4 and sodium is too expensive
117
How is a nitrile reduced to a carboxylic acid
Reflux with a dilute HCl

Chemistry 2 (10 decks)

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