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A level Chemistry > Halogenoalkanes > Flashcards

Halogenoalkanes Flashcards

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1
Q

Chloroform is part of a ?

A

halogenoalkane

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2
Q

What is a halogenoalkane

A

It’s an alkane where one molecule is replaced by a halogenoalkane

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3
Q

When a molecule is an alkane we write what?

so what do we name this alkane ?

A

“Ane” at the end of the name

methane

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4
Q

What is this molecule called?

A

Fluoromethane

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5
Q

what’s the name of this molecule?

A

bromoethane

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6
Q

What is this molecule called

A

1-bromopropane

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7
Q

What is this molecule called

A

2-bromopropane

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8
Q

what do we call this molecule

A

2-chlorobutane

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9
Q

What do we call this molecule

and what does the position number tell us

A

3-fluoropentane

the 3 is the position number of the fluorine and tells us where the halogen is located in the carbon chain

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10
Q

What is this molecule called

A

1-fluorobutane

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11
Q

what do we call this molecule

A

2-iodohexane

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12
Q

What is the general formula for halogenoalkanes?

A

CnH2n+1

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13
Q

What halogenoalkane is this molecule?

A

secondary as the carbon bonded to chlorine is bonded to 2 more carbons

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14
Q

What type of halogenoalkane is this

A

tertiary as the carbon bonded to chlorine is bonded to 3 more

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15
Q

What type of halogenoalkane is this

A

primary as the carbon bonded to Chlorine is bonded to a single carbon

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16
Q

All halogenoalkanes are…

as the length of the halogenoalkane carbon chain increases…

A

polar molecules
meaning they experience van der waals forces and dipole dipole forces

as the length increases the van der waals forces increases

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17
Q

are halogenoalkanes soluble in water?

A

Halogenoalkanes are only slightly soluble in water
as the length of the halogenoalkane increases we have more C-C bonds and C-H bonds which are non polar so solubility increases as non polar substances are highly insoluble in water

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18
Q

what is a nucleophilic substitution?

A

Where a nucleophile e.g cyanite, hydroxide etc is substituted for a halogen

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19
Q

what’s happening here

A

Halogenoalkanes are polar so the Br molecule has a delta negative charge whereas the carbon bonded to bromine has a positive one

The hydroxide ion has a lone pair and that line pair is attracted to the Positive carbon bit so the whole molecule acts as an electrophile (proton acceptor / base ) meaning the lone pairs arrow goes from the lone pair to the carbon

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20
Q

What’s happening here

A

Since a new bond is formed between the carbon and the hydroxide ion,
another bond has to break as carbon can only make 4 bonds
the carbon bonded to bromine breaks
making an arrow from the bond pointing to bromine making bromine be substituted for OH like this

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21
Q

What’s the structural formula (Ionic equation) of this molecule

A

CH3CH2CH2Br + OH- —> CH3CH2CH2OH + Br-

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22
Q

what’s the structural formula (full equation) of this equation?

A

CH3Cl + OH- + Na+ —> CH3OH + NaCl

full equation =

CH3Cl + NaOH —> CH3OH + NaCl

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23
Q

What is the reagent and nucleophile in this reaction?

A

OH- = nucleophile

NaOH is the reagent

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24
Q

What is the reagent and nucleophile in this reagent?

A

KCN (potassium cyanide) is the reagent

whereas CN- (cyanite) is the nucleophile

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25
Q

what is the reagent and nucleophile in this reaction

A

NH3 is the reagent

and NH3 is the nucleophile

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26
Q

What is a nucleophile and reagent?

A

Nucleophile = donates an electron pair to form a covalent bond

reagent= substance that is physically added to the system

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27
Q

Identify the reagent and nucleophile

A 
Nucleophile = CH3CH2O
Reagent = CH3CH2ONa
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28
Q

Deduce what products would form and the arrow

What is the product called?

A

OH points from its line pair to the middle C bonded to Br & C-Br bond breaks substituting OH for Br and making it a single Br- product

the OH on the molecule is called an alcohol

so when an hydroxide forms a nucleophilic substitution reaction is always forms an alcohol

29
Q

In hydroxide reactions in nucleophikic substitution we can use NaOH and KOH to make our alcohol.
What are they examples of?

A

Reagents

30
Q

In order for the halogenoalkanes to undergo nucleophilic substitutions with hydroxides (-OH) the reagents need to be…

A

(NaOH & KOH) Reagents need to be in the aqueous state

they need to be dissolved in water

31
Q

Increasing the temperature…

A

increases the rate of reaction so chemists heat the reaction with the reagents (NaOH & KOH) to get faster results

32
Q

What would form?

A

CN- would form a bond with the C bonded to I breaking the bond with I

so I would be substituted for CN forming also I-

The cyanide ion behaves weird. Carbon behaves as a negative ion although technically Nitrogen is more electronegative giving it a negative charge so both C and N have lone pairs

33
Q

What happens in this reaction

also what homologous series is this in?

A

1) write delta positive and negative charges
2) CN- forms a bond with C bonded to Br breaking also the C-Br bond replacing CN with Br with products being Br-
it’s in the nitrile homologous series
halogenoalkanes undergo nucleophilic substitution with cyanites to form nitriles

34
Q

What is this molecule called

A
  1. ethanenitrile
  2. propanenitrile
  3. butanenitrile
35
Q

To produce nitriles we can heat what?

What are the other conditions required to produce a nitrile as well in nucleophilic subsitution?

A

heat the reagent KCN ( potassium cyanide) or NaCN (sodium cyanide)

heating the reaction increases the rate of reaction

dissolving NaCN and KCN in liquid ethanol making it nitriles rather than alcohols

36
Q

1-iodopropane undergoes nucleophilic substitution with sodium cyanide
complete the equation for this reaction..

A

CH3CH2CH2CHCI + NaCN —> CH3CH2CH2CHCN + NaI

37
Q

Why do we need to dissolve the KCN and NaCN in ethanolic liquid solution? why not just water

A

if we dissolve the solution in water it will turn into an alcohol
as the OH in water can act as a nucleophile and react
if we dissolve it in liquid ethanol there won’t be hydroxide ions and ensure the cyanide ions react

38
Q

How many mechanism steps does ammonia have?

A

2

39
Q

Ammonia has these steps explain them

A

ammonia lone pair forms a bond with the carbon bonded to halogen (Cl) breaking the C-Cl bond replacing the NH3 making it a + ion as it gained electrons

to make it to NH2 we add another ammonia nucleophile and react it’s lone pairs with 1 hydrogen and breaking the bond of hydrogen it’s reacting with nitrogen forming NH2 and NH4Cl

Why doesn’t the nitrogen form a bond with ammonia? because it’s more electronegative forming a delta neg charge and allowing the H to be positive it forms a bond with the lone pair of NH3

40
Q

Write the equation for this reaction

A

CH3CH(Br)CH3 + 2NH3 —> CH3CH(NH2)CH3 + NH4Br

41
Q

What’s the overall equation for the reaction between 1-chloroethane and ammonia to form an amine?

A

CH3CH2Cl + 2NH3 —> CH3CH2NH2 + NH4Cl

42
Q

To form animes, we react halogenoalkanes with

A

ammonia (NH3) and dissolve it in ethanol

and also form amines from halogenoalkanes by heating the reaction, using high pressures and using excess ammonia

43
Q

The rate of reactions of halogenoalkanes is determined by

A

bond enthalpy
so the lower the bond enthalpy the fast the reactions
which in this case halogens, iodine has the lowest bond enthalpy so iodine reacts faster

44
Q

How do you measure the reactivity of halogenoalkanes?

A

Dissolve the halogenoalkane in ethanol
then add silver nitrate (AgNO3) and water and measure the time it takes for a precipitate to form
the quicker the precipitate forms the faster the rate of reaction

45
Q

What is an elimination reaction?

A

2 things occur,

1) 2 sigma bond break
2) a pi bond forms
e. g

46
Q

if we react 2-bromopropane with NaOH (aq) we get…

A

an nucleophilic substitution reaction where the product alcohol is formed making it propanol and NaBr

47
Q

But if we react 2-bromopropane with ethanolic sodium hydroxide NaOH instead we get…

A

an elimination reaction producing an alkene

48
Q

What is the trend following to get an elimination reaction and nucleophilic substitution?

A

If we react any halogenoalkane with an aqueous hydroxide (NaOH/KOH etc.) these reactants undergo an nucleophilic substitution reaction and produce an alcohol

but when we react that same halogenoalkane with ethanolic hydroxides they undergo elimination reaction producing an alkene

49
Q

What’s produced in the following reactions?

a) 1-iodobutane reacts with ethanolic potassium hydroxide
b) 1-iodobutane reacts with aqueous sodium hydroxide

A

a) . elimination reaction producing an alkene

b) nucleophilic substitution producing an alcohol

50
Q

How do we increase the rate of reaction of elimination reactions?

A

heat the mixture

51
Q

In a nucleophilic substitution reaction state the conditions

A 
the reagent (NaOH/KOH etc) needs to be aqueous 
the reagent needs to be diluted and in lower temperatures

in exam you need to state that it needs to be in aqueous and lower temperature to increase the chances of nucleophilic substitution occurring

52
Q

in elimination reaction state the conditions

A

reagent needs to be dissolved in ethanolic solution
needs to be concentrated (NaOH/KOH)
they need to be in high temperatures as well to increase the chances of elimination occurring

53
Q

The brønsted lowry model defines a base as an

A

proton acceptor

54
Q

depict what is acting as a base

A

1) HO isn’t acting as a base as it’s forming a bond meaning it’s donating it’s electrons
2) HO acting as a base as its accepting a bond which is broken

another example

water first isnt acting as a base as its forming a bond
water in second is accepting a H+ ion broken from O so it’s acting as a base

55
Q

What is the role of -OH in this reaction?

A

OH is acting as a base

56
Q

How do we represent with curly arrows 2 sigma bonds breaking and a oi bond breaking in this example

A

1) arrow tells that the hydroxide line pair forms a bond with hydrogen where the hydroxide ion acts as a base

2) arrow telling us the carbon hydrogen bond is breaking and a pi bond is forming where the arrow is pointing
3) arrow tells us the carbon bromine bond is breaking

but the the carbon hydrogen bond doesn’t break on its on. for it to occur (elimination) we need to dissolve out hydroxides in ethanol

57
Q

What are the final products?

A

alkene and water and the halogen

58
Q

explain what’s happening here

A

1) hydroxide ion forms a bond with hydrogen breaking the bond with carbon
2) carbon iodine bond breaks making C=C alkene making water and I-

59
Q

Which hydrogen is removed in elimination reaction

in this reaction

A

we can only remove the hydrogens next to Iodine and below highlighted

60
Q

what’s the trend of removing hydrogen

A

we can only remove hydrogens adjacent to the halogen

61
Q

Show us an example of why you can remove 2 and still get the same product

A

hydrogens can be removed carbon adjacent to the carbon halogen bond

62
Q

Identify the error of this elongation reaction drawn

A

1) Hydroxide ion is missing a lone pair

2) the curly arrow from C—C to C—H should be reverse like this

63
Q

What products do we get if we react ethanolic sodium hydroxide with 2-chlorobutane?

A

depending on where the hydrogen is removed we can get 2 products
1) if we remove the hydrogen from the first carbon we get but-1-ene
2) if we remove a hydrogen from the third carbon we get but-2-ene
both of these are examples of structural isomers as they have the same molecular formula but different structural formulas

64
Q

Alkenes have restricted rotation around their double bond. This means that if an alkene has 3 substituents, it will have

A

E-Z isomers
2 substituents being CH3
so the reaction produces both E and Z isomer

bcs it has 2 substituents we get E-but-2-ene and Z-but-2-ene

65
Q

How do these isomers look like

E-but-2-ene and Z-but-2-ene

A

1) substituents being on the opposite sides so it’s E but 2 ene
2) substituents in the same side so it’s a Z but 2 ene

66
Q

What products do we get in 2-chlorohexane

A

we get Hex-1-ene and hex-2-ene

and hex-2-ene E/Z isomers

67
Q

how do we write the equation from this reaction?

A

CH3CH2CH2Br + KOH —> C3H6 + KBr + H2O

ionic

CH3CH2CH2Br + OH- —> C3H6 + H2O + Br-

since the hydrogen can only be removed from the second carbon as that’s the one adjacent so it can’t produce any position isomers so we write the molecular
formula

68
Q

Write the equation for this reaction

A

because we are producing different position isomers we need to write the structural formula

1) ionic
2) full equation

A level Chemistry (12 decks)

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