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Chemistry 2 > Theory > Flashcards

Theory Flashcards

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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
Q

What type of reaction do alkenes undergo

A

Electrophilic addition

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26
Q

How do you know what product will be the most stable in a unsymmetrical alkane when a hydrogen halide is being added

A

Carbon with the most alkyl groups is the most stable
Feeds the most electrons into the carbon atom
Forms a more stable carbocations

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27
Q

Why are small alcohols soluble in water

A

H bonds form between water and the OH group

Most of the chain is polar so it fully dissolves

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28
Q

Why are long alcohols not as soluble

A

Most of the chain isn’t polar so can’t h bond with the water

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29
Q

Why do alcohols have a low volatility

A

They can h bond between molecules

Takes lots of energy to overcome

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30
Q

Why do aldehydes have to be distilled off as soon as it’s formed

A

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

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31
Q

What is the only way of oxidising a tertiary alcohol

A

Burning

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32
Q

What type of reaction is it when haloalkanes react with alkali

A

Nucleophilic substitution

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33
Q

Why do iodo alkanes get hydrolysed the fastest

A

They have the weakest bond (lowest bond enthalpy) so requires less energy to overcome

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34
Q

What are cfcs

A

Only contain carbon fluorine and chlorine

All h atoms have been replaced by halogens

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35
Q

How is ozone formed

A

O2 -> O+O (UV)

O2 + O -> O3

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36
Q

Why are cfcs bad

A

Catalyse break down of ozone
Causing holes in ozone in atm
Let in harmful Uv

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37
Q

Write the mechanism of cfcs destroying the ozone

A

CF2Cl2 -> 🖤CF2Cl + Cl🖤
Cl🖤 + O3 -> O2 + ClO🖤
ClO🖤 + O -> O2 + Cl🖤

Overall = O3 + O -> 2O2

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38
Q

Why are Cl🖤 so bad

A

They are regenerated
So are a catalyst
So 1 Cl🖤 destroys lots of ozone before it forms a stable compound

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39
Q

What other compound besides Cl🖤 destroys the ozone

A

NO🖤

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40
Q

Why is the kekule model incorrect

A

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.

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41
Q

What reaction does benzene undergo

A

Electrophilic substitution;

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42
Q

Why is a halogen carrier needed for reactions with benzene

A

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

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43
Q

Draw the mechanisms for benzene + Br2

A

-

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44
Q

What reactants are needed for a friedel craft alkylation

A

Haloalkane
AlCl3
Benzene

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45
Q

What reactants are needed for a friedel craft acylation

A

Acyl chloride
Alcl3
Benzene

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46
Q

What is the catalyst used in the format of nitrobenzene

A

Conc H2SO4

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47
Q

What is the equation of the formation of the nitronium ion

A

Hno3 + H2SO4-> h2no3+ + hso4-

H2no3 -> no2+ + h2o

48
Q

Why does the temp need to be kept below 55 for the nitration on benzene

A

To stop multiple substitutions which make a explosive substance

49
Q

Draw the nitratation of benzene mechanism

A

-

50
Q

Why is phenol more reactive than benzene

A

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
Q

Why are some groups donating

A

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
Q

What are the electron donating groups

A

Nh2
oh
EDG

53
Q

Why are some groups withdrawing

A

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
Q

What is the product of bromine + phenol

A

2,4,6 tribromophenol

55
Q

How do you know phenol has reacted with bromine

A

Forms precipitate in water

Decolourises

56
Q

What is the ph of phenol

A

3/4

Weak acid

57
Q

Why does phenol not react with sodium carbonate

A

Phenol isn’t a strong enough acid

58
Q

What is used to reduce aldehydes and ketones back to alcohols

A

NaBH4

Dissolved in water and methanol

59
Q

What supplies the nucleophile in the reduction of ketones and aldehydes

A

H- from NaBH4

It has a lone pair of electrons

60
Q

What compound does HCN make with carbonyl compounds

A

Hydroxynitriles

61
Q

What type of solution is HCN

A

Weak acid

62
Q

What is the electrophile in the formation of hydroxynitrileS

A

CN-

63
Q

What type of reaction is the reduction of ketones/aaldehydes

A

Nucleophyllic addition

64
Q

What type of reaction is the formation of hydroxynitriles

A

Nucleophilic addition

65
Q

What precautions are used in the lab when making a hydroxynitriles

A

Used acidified sodium cyanide instead of HCN because HCN is highly toxic
Done in fume cupboards

66
Q

Why are carboxylic acids soluble in water

A

Can h bond due to polar oh and o group

67
Q

What is the fg of acyl chlorides

A

COCl

68
Q

How are acyl chlorides made

A

Carboxylic acid + SOCl2

69
Q

What happens when acyl chloride + water

A

Carboxylic acid + HCl
Vigorous
Cold

70
Q

What happens when acyl chloride + alcohol

A

Ester + HCl
Vigorous
Room temp

71
Q

What happens when acyl chloride + ammonia

A

Primary amide
+ HCl
Violent
Room temp

72
Q

What happens when acyl chloride + amines

A

Secondary amide + HCl
Violent
Room temp

73
Q

What products would u actually get in a lab when ammonia + ethanoyl chloride

A

Ethanamide
HCl
Ammonium chloride
Because the HCl product reacts with the ammonia reactant

74
Q

Which is the most effectuent way of making an ester

A

Alcohol + acyl chloride
Faster
And irreversible

75
Q

What reaction type do acyl chlorides undergo

A

Nucleophilic addition elimination

76
Q

What is the reaction between ethanoyl chloride + phenol

A

Phenyl ethanoate + HCl

77
Q

Describe the formation of an ester from alcohol + carboxylic acid

A

Conc H2SO4 catalyst
Reversible = need to separate product as it’s made by distillation or reflux
Water produced

78
Q

Describe estérification from alcohol and acid anhydride

A

No catalyst
Separate by fractional distillation
Ester + carboxylic acid produced

79
Q

Describe base hydrolysis

A

Splits ester into carboxylic acid and aldohol
Reflux
Dilute acid
Reversible reaction

80
Q

How do u keep the postsotion of eqm to the right in acid hydrolysis

A

Add lots of water

81
Q

Explain base hydrolysis

A

Reflux
Dilute alkali (naoh)
Forms carboxylate salt and alcohol

82
Q

What is an amine

A

H replaced in NH3 by an organic group

83
Q

What type of solution are amines

A

Basic

84
Q

What are amines bases

A

There is a lone pair on NH3

So it can accept a proton

85
Q

What is the reaction with ethylamine + HCl

A

Ethylammonium chloride

Ch3Ch2NH3+Cl-

86
Q

How do you make amines

A

Haloalkane + ethanolic ammonia

87
Q

How do you separate primary secondary and tertiary amines

A

Fractional distillation

88
Q

Why do you get a mixture of primary secondary and tertiary amines

A

More than one H is likely to be substituted on NH3

89
Q

What is the reaction of ammonia + bromoethane

A

Ethylamine + NH4Br

90
Q

How do you form diethylamine

A

Nh3 + ethylamine + bromoethane

91
Q

How do you make aromatic amines

A

Reduce nitrobenzene

Nitrobenzene + tin metal + conc HCl
Reflux
Add NaOH

Makes phenyl amine + 2H2O

92
Q

What are amides

A

Have the functional group conh2

93
Q

Why do amides behave differently to amines

A

The carbonyl group on CONH2 pull electrons away from the Nh2

94
Q

What is a secondary amide

A

One of the H is replaced by a methyl group

95
Q

Amino acid + alkali

A

Forms salt + water

96
Q

Amino acid + acid

A

Salt

97
Q

Amino acid + alcohol

A

Ester + H2O

H2SO4 catalyst

98
Q

What is a chiral center

A

Carbon atom with 4 different groups attached

99
Q

What are optical isomers

A

Mirror images of each other
Can’t be super imposed
Optically active

100
Q

What does optically active mean

A

They rotate the plane polarised light

101
Q

What are polymers

A

Long chains of monomers joined together

102
Q

Wh at are addition polymers

A

Double bond opens up

103
Q

What is condensation polymerisation

A

Formed from 2 types of monomers
Functional groups link
Small molecules lost (H2O)

104
Q

How are polymers broken down

A

Hydrolysis
Water added back
Done with acid abs base

105
Q

What is acid hydrolysis

A

Add H+

Forms dicarboxylic acid and diamine

106
Q

What is base hydrolysis

A

Dicarbocylate acid salt

Diol

107
Q

What is a CN-

A

A nucleophile

108
Q

What will CN- react with

A

React with carbon centres With a partially positive charge
Forming a new c -c bond

Forms a nitrile

109
Q

How to increase length of carbon chain by addicting cyanide

A

Add HCN to slightly positive carbon

110
Q

What type of reaction is haloalkanes + cyanide

A

Nucleophilic subsituation

111
Q

How to form nitrile but from haloalkane

A

Reflux haloalkane with KCN in ethanol

Using nuclephylic substitution

112
Q

How do you form a hydroxynitriles

A

Aldehyde/ketone + HCN

113
Q

Why are nitrile groups useful in synthesis

A

Very reactive so can be replaced by other fg

114
Q

How to reduce a nitrile to a primary amine

A

LiAlH4
+ Dilute acid

Or

Sodium metal + ethanol

115
Q

What method is used to reduce nitriles in industry

A

Adding h gas and metal catalyst (Ni) at high Temp and pressure by catalytic hydrogenation

116
Q

Why is catalytic hydrogenation used in industry

A

LiAlH4 and sodium is too expensive

117
Q

How is a nitrile reduced to a carboxylic acid

A

Reflux with a dilute HCl

Chemistry 2 (10 decks)

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