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Chemistry Module 4- Core Organic Chemistry > Haloalkanes > Flashcards

Haloalkanes Flashcards

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1
Q

What is the general formula of haloalkanes

A

C2n H2n+1 X

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2
Q

What is a haloalkane

A

An alkane with at least one halogen atom in place of a hydrogen atom

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3
Q

Why is C-X polar

A

Because the halogen is more electronegative than the carbon atom

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4
Q

What is a nucleophile

A

An electrophile pair donor

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4
Q

What are examples of nucleophiles

A

OH-
CN-
NH3
Water is a nucleophile but reacts more slowly

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5
Q

What are primary secondary and tertiary haloalkanes

A

It depends on the position of the halogen in the carbon chain. Primary has one alkyl group secondary has 2 and tertiary has 3

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6
Q

What is the reaction for nucleophilic substiution

A

Haloalkane—> Alcohol

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7
Q

What are the conditions for nucleophilic substitution

A

Warm/hot

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8
Q

What are the reagents and type of reaction for nucleophilic substitution

A

NaOH (aqueous)
Type- Substitution

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9
Q

What is the conversion for nucleophilic substitution in CN

A

Haloalkane- Nitride ( R-C(triple) N)

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10
Q

What are the conditions for the reaction with CN

A

In ethanol

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11
Q

What are reagents and type of reaction for CN

A

KCN/NaCN
Substitution

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12
Q

How does the alcohol form during nucleophilic substitution

A

The OH- behaves as a nucleophile and has a lone pair of electrons and these are attracted and donated to the positive carbon.
Leads to the formation of a dative covalent bond between the carbon atom and the halogen atom in the OH

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13
Q

How do the products form

A

The C-H bond breaks by heterolytic fission and both electrons from the bond move to the halogen forming a halide ion

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13
Q

What is hydrolysis

A

A reaction with water or hydroxide ions that breaks a bond in a compound turning it into 2 compounds

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14
Q

What is the hydrolysis reaction with OH-

A

CH3CH2CH2CH3X + OH- —–> CH3CH2CH2CH2OH+ X-

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14
Q

What is the hydrolysis reaction with H20

A

CH3CH2CH2CH2X+ H20 ——> CH3CH2CH2CH2OH + HX

15
Q

What is the hydrolysis reaction for the halides

A

Add ethanol as the solvent is water and organic as its imissible so dont mix so the alovent allows it to mix so the reaction can occur

16
Q

Why do you add AgNO3 for the reaction

A

To form the precipitate with halide ions then heat in a water bath for a constant temperature

17
Q

How do you compare the reactivities of the halides

A

Set up 3 test tubes each containing a different haloalkane, ethanol as a solvent and silver nitrate solution
Warm the tubes in a water bath (50-60 degrees)
Time how long it takes for ppt to form
A pale yellow precipitate quickly forms with 2-iodopropane so iodoalkanes are the most reactive. Bromo alkanes react slower than iodoalkanes to form a cream precipitate and chloroalkanes form a white precipitate the slowest

18
Q

Why was a water bath used

A

To ensure all experiments are performed at the same temperature

19
Q

How can the rate of hydrolysis be found

A

By calculating 1 divided by time taken for ppt to form

20
Q

Why does it take longer for hydrolysis to take place

A

As the rate of hydrolysis increases the strength of the carbon-hydrogen bond decreases. Higher bond enthalpies mean there are stronger bonds so the energy required to break the C-X bond is greater so takes longer for hydrolysis to take place

21
Q

How do you determine the rate of hydrolysis of a haloalkane

A

As you go down group 7 the strength of the C-X bond decreases so the lower the bond enthalpy the faster the rate of hydrolysis

22
Q

How many oxygen atoms are bonded to eachother for the ozone

A

3

23
Q

Why is the ozone layer useful to humans

A

It absorbs harmful UV radiation which could cause skin cancer from the sun and converts it into heat

24
Q

What are the equations with oxygen

A

O2——>2O
O2+O—–>O3 (+heat)
O3——–>O2+O

25
Q

How is the concentration of ozone maintained in the ozone layer

A

It is kept at equilibrium as a reversible reaction
O2+O —–> O3
The rate of formation = the rate of decomposition

26
Q

What are CFCS

A

Well known haloalkanes which only contain carbon fluorine and chlorine as all the halogens have been replaced

27
Q

What were CFCS used as

A

Aerosols and cooling devices

28
Q

Why were CFCS used a refrigerants

A

They are non toxic
Non flammable
Very stable

29
Q

Why do CFCS only break down high in the atompshere

A

they form chlorine radicals which catalyse the breakdown of ozone

30
Q

What are 2 alternatives to CFCS

A

HCFC AND HFC

31
Q

How would the mass of a haloalkane compare with the mass of an alkane of the same carbon chain

A

Greater as the mass of a halogen is greater than the mass of a hydrogen

32
Q

How do CFS break down the ozone layer using radical substitution (initiation)

A

CFCl3———> Cl+C*FCl2

33
Q

How do CFS break down the ozone layer using radical substitution (propagation)

A

Cl* + O3——-> ClO + O2
ClO+ O——-> Cl+ O2

33
Q

What is the overral equation for the catalysation

A

O3+ O————> 2O2 this is the same for all ozone degradation reactions

34
Q

How are nitrogen oxides produced

A

Car and aircraft engines and thunderstorms

35
Q

What are the 2 propagation steps for nitrogen oxide

A

NO* + O3———–> NO2* + O2
NI2* + O————-> NO* + O2

36
Q

What is the overral equation for nitrogen oxide

A

O3+O———>2O2

37
Q

Why are all of these reactions chain reactions

A

The radicals are used in step 1 and regenerated in step 2

Chemistry Module 4- Core Organic Chemistry (7 decks)

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