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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
what is the reagent and nucleophile in this reaction
NH3 is the reagent | and NH3 is the nucleophile
26
What is a nucleophile and reagent?
Nucleophile = donates an electron pair to form a covalent bond reagent= substance that is physically added to the system
27
Identify the reagent and nucleophile
``` Nucleophile = CH3CH2O Reagent = CH3CH2ONa ```
28
Deduce what products would form and the arrow | What is the product called?
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
In hydroxide reactions in nucleophikic substitution we can use NaOH and KOH to make our alcohol. What are they examples of?
Reagents
30
In order for the halogenoalkanes to undergo nucleophilic substitutions with hydroxides (-OH) the reagents need to be…
(NaOH & KOH) Reagents need to be in the aqueous state | they need to be dissolved in water
31
Increasing the temperature…
increases the rate of reaction so chemists heat the reaction with the reagents (NaOH & KOH) to get faster results
32
What would form?
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
What happens in this reaction | also what homologous series is this in?
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
What is this molecule called
1. ethanenitrile 2. propanenitrile 3. butanenitrile
35
To produce nitriles we can heat what? | What are the other conditions required to produce a nitrile as well in nucleophilic subsitution?
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
1-iodopropane undergoes nucleophilic substitution with sodium cyanide complete the equation for this reaction..
CH3CH2CH2CHCI + NaCN —> CH3CH2CH2CHCN + NaI
37
Why do we need to dissolve the KCN and NaCN in ethanolic liquid solution? why not just water
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
How many mechanism steps does ammonia have?
2
39
Ammonia has these steps explain them
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
Write the equation for this reaction
CH3CH(Br)CH3 + 2NH3 —> CH3CH(NH2)CH3 + NH4Br
41
What’s the overall equation for the reaction between 1-chloroethane and ammonia to form an amine?
CH3CH2Cl + 2NH3 —> CH3CH2NH2 + NH4Cl
42
To form animes, we react halogenoalkanes with
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
The rate of reactions of halogenoalkanes is determined by
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
How do you measure the reactivity of halogenoalkanes?
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
What is an elimination reaction?
2 things occur, 1) 2 sigma bond break 2) a pi bond forms e. g
46
if we react 2-bromopropane with NaOH (aq) we get…
an nucleophilic substitution reaction where the product alcohol is formed making it propanol and NaBr
47
But if we react 2-bromopropane with ethanolic sodium hydroxide NaOH instead we get…
an elimination reaction producing an alkene
48
What is the trend following to get an elimination reaction and nucleophilic substitution?
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
What’s produced in the following reactions? a) 1-iodobutane reacts with ethanolic potassium hydroxide b) 1-iodobutane reacts with aqueous sodium hydroxide
a) . elimination reaction producing an alkene | b) nucleophilic substitution producing an alcohol
50
How do we increase the rate of reaction of elimination reactions?
heat the mixture
51
In a nucleophilic substitution reaction state the conditions
``` 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
in elimination reaction state the conditions
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
The brønsted lowry model defines a base as an
proton acceptor
54
depict what is acting as a base
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
What is the role of -OH in this reaction?
OH is acting as a base
56
How do we represent with curly arrows 2 sigma bonds breaking and a oi bond breaking in this example
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
What are the final products?
alkene and water and the halogen
58
explain what’s happening here
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
Which hydrogen is removed in elimination reaction | in this reaction
we can only remove the hydrogens next to Iodine and below highlighted
60
what’s the trend of removing hydrogen
we can only remove hydrogens adjacent to the halogen
61
Show us an example of why you can remove 2 and still get the same product
hydrogens can be removed carbon adjacent to the carbon halogen bond
62
Identify the error of this elongation reaction drawn
1) Hydroxide ion is missing a lone pair | 2) the curly arrow from C—C to C—H should be reverse like this
63
What products do we get if we react ethanolic sodium hydroxide with 2-chlorobutane?
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
Alkenes have restricted rotation around their double bond. This means that if an alkene has 3 substituents, it will have
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
How do these isomers look like | E-but-2-ene and Z-but-2-ene
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
What products do we get in 2-chlorohexane
we get Hex-1-ene and hex-2-ene | and hex-2-ene E/Z isomers
67
how do we write the equation from this reaction?
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
Write the equation for this reaction
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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