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Chemistry 2.0 > 3.3 Haloalkanes > Flashcards

3.3 Haloalkanes Flashcards

1
Q

Outline the following steps in the mechanism for the reaction of methane with fluorine to form fluoromethane

A
  1. Initiation step
    F2->2F.
  2. First propagation step
    CH4 +F. -> C.H3 + HF
  3. Second propagation step
    C.H3 + F2 -> CH3F +F.
  4. Termination step
    C.H3 +F. -> CH3F
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2
Q

What does it mean when a haloalkane is described as primary, secondary and tertiary

A

Primary : carbon bonded to halogen is bonded to only one other carbon atom
Secondary : Carbon bonded to halogen is bonded to two other carbon atoms
Tertiary : Carbon bonded to halogen is bonded to three other carbon atoms

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3
Q

State the essential condition for free radical substitution and why it is necessary

A

UV light
- as it provides the energy to break the halogen-halogen bond to form free radicals and start the reaction

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4
Q

Define free radical

A

A species with an unpaired electron

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5
Q

What is homolytic fission

A

When the halogen - halogen bond is broken

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6
Q

Write overall reaction for reaction of chlorine with methane to form chloromethane (CH3CL)

A

Initiation step : Cl2 -> 2Cl.
Propagation step 1 : CH4 + Cl. -> C.H3 + HCl
Propagation step 2 : C.H3 + Cl2 -> CH3Cl + Cl.
Termination step : Cl. + C.H3 -> CH3Cl

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7
Q

Write overall equation for reaction of chlorine with methane to form trichloromethane

A

CH4 + 3CL2 -> CHCL3 + 3HCl

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8
Q

Methane reacts with IBr to form many products. Outline the mechanism that produces iodomethane and hydrogen bromide

A
  • UV light needed
    Initiation step : IBr -> Br. + I.
    Propagation step 1: CH4 + Br. -> C.H3 + HBr
    Propagation step 2 : C.H3 + IBr -> CH3I + Br.
    Termination step : I. + C.H3 -> CH3I
    Br. + C.H3-> CH3Br
    C.H3 + C.H3 -> C2H6
    (there are more termination steps but you only need to show 3)
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9
Q

Which species is produced in a propagation step during reaction of propane with an excess of chlorine in presence of UV light
1. H.
2.C3H5CL
3.C3H6CL2
4.C6H14

A
  1. C3H6CL2
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10
Q

How to reduce amount of further substitution

A

Use excess alkane

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11
Q

What are CFCS

A

Haloalkanes that contain both chlorine and fluorine

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12
Q

Chlorotrifluoromethane (CClF3) decomposes in presence of UV light forming a reactive intermediate that catalyses the decomposition of ozone. Write an equation to show how CClF3 decomposes to form the reactive intermediate.
Write two equations to show how this reactive intermediate is involved in catalysing the decomposition of ozone

A

CFCL3 -> C.FCL2 + Cl.
Cl. + O3 -> ClO. + O2
ClO. +O3 -> Cl. + 202

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13
Q

Identify condition that causes CCl4 to break in upper atmosphere

A

UV light

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14
Q

Small amount of freon CF3Cl has mass 1.78 x 10^-4 kg goes into a room with a volume of 100m^3. Calculate number of freon molecules in a volume of 500cm^3
Avogadro constant = 6.022 x 10^23 mol^-1

A

Mr of Freon : 104.5
moles in freon = (1.78 x 10^-4) divided by 104.5 = 1.7 x 10^-3
Number of molecules = (1.7 x10^-3) x (6.022 x 10^23) = 1.02 x 10^21
molecules in 500cm^3
(1.02 x 500 x 10^-6) divided by 100 = 5.1 x 10^15 (2.s.f)

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15
Q

State role of chlorine atoms in the ozone layer reactions

A

Acts as a catalyst
This is because it is regenerated and is unchanged at the end of

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16
Q

Boiling point of iodomethane is higher than that of fluoromethane even though electronegativity of iodine is less than that of fluorine
Why does iodomethane have a higher boiling point

A

Iodine is bigger than fluorine so van de waals forces between CH3I molecules are stronger than those between CH3F mlecules
The permanent dipole-dipole forces in CH3F are stronger than CH3I. However van de waals forces are stronger than the permanent dipole-dipole forces

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17
Q

In upper atmosphere it is more likely for CBrF3 t produce bromine atoms than it is for CClF3 to produe chlorine atoms. Suggest why?

A

C-Br bonds weaker than C-Cl bonds / C-Br bond enthalpy is ess tha that for C-Cl

18
Q

Write two equations to show how bromine atoms Br. acts as a catalyst in decomposition of ozone. Explain how equations show that bromine behaves as a catalyst

A

Br. + O3 -> Br.O + O2
.BrO + O3 -> Br. 2O2
Bromine is regenerated /
Unchanged at the end /
has not been used up

19
Q

Chemists wanted to ban the use of CFCS
Modern refrigerators use pentane rather than CFCS as refrigerants. Sate why pentane is a more enviromentally acceptable refrigarent.

A

Pentane doesnt contain chlorine
as chlorine causes ozone depletion

20
Q

Identify the species formeed from CClF3 that is responsible for the catalytic decomposition of ozone in upper atmosphere

A

Cl.

21
Q

Write overall equation to show decomposition of ozone into oxygen

A

2O3 -> 302

22
Q

State benefit to life on earth of ozone in the upper atmosphere

A

Absorbs harmful ultraviolet / UV (light/radiation)

23
Q

State why use of CFCS wasnt restricted until after Rowland and Molina published their reserch

A

Lack of evidence ozone was depleted
Lack of alternatives to CFCS
Hard to obtain international agreement

24
Q

Explain how trichlorofluoromethane (a CFC) is able to contribute to global warming

A

It absorbs infrared rotiation
Molecule has polar bonds

25
Q

State how CFCS form chlorine atoms in upper atmosphere

A

C-Cl bonds broken with homolytic fission

26
Q

Which statement about ozone is not correct
1. It absorbs harmful ultraviolet radiation in upper atmosphere
2. Its decomposition is catalysed by chlorine molecules
3. It decomposes to form oxygen
4. Ozone holes are regions of the upper atmosphere where there is a reduced concentration of ozone

A
  1. it decomposes to form oxygen
27
Q

State meaning of term nucleophile

A

Electron pair donor

28
Q

State meaning of term substitution, as applied tpo nucleophilic substitution

A

Replacement of the halogen atom by the nucleophile

29
Q

Explain why an excess of ammonia is needed to produce a high yield of ehtlyamine (CH3CH2NH2) when ammonia reacts with bromoethane

A

Ethylamine is a nucleophile/could react further /coud make secondary / tertiary amines / to make reaction of ammonia more likely / to minimise further substitution

30
Q

Give IUPAC name of CH3CH2CN

A

Propanenitrile

31
Q

Explain why 2-bromopropane is attacked by a nucleophile

A

Bromine is more elctronegative than carbon
Carbon is partially positive / electron deficient
Lone pair on nucleophile donated to partially positive carbon

32
Q

Give equation for preparation for reaction of ammonia with 6-bromohexylamine to form 1,6 - diaminohexane

A

Br-(CH2)6-Br + 4NH3 -> H2N - (CH2)6 - NH2 + 2NH4Br

33
Q

Which species could act as a nucleophile
1. BH3
2. NH4^+
3. PH3
4. SiH4

A

2.NH4^+

34
Q

What is the organic product of the reaction of 1-bromopropane with a solution of potassium cyanide in aqeous ethanol

A

Butanenitrile

35
Q

What is the reagent, conditions and products of nucleophilic substitution by OH^- ions
State the nucleophile

A

Reagent : NaOH or KOH
Conditions : aqeous solvent
Products : alcohol
Nucleophile : Hydorxide ion

36
Q

What is the reagent, conditions,nucleophile and products by CN- ions

A

Reagent : KCN
Conditions : water and ehtanol solvent
Type of product : Amine

37
Q

What is the reagent, conditions, nucelophiles and products of nucleophilic substitution by NH3

A

Nucleophile : CN-
Conidtions : Ethanol solvent, heat, and pressure
Type of product: Amine

38
Q

Chloroethane reacts with potassium hydorixde in the presence of propan-1-ol to form ethene
State role of potassium hydroxide and the role of propan-1-ol in the reaction

A

Role of KOH : Acts as a base
Role of propan-1-ol : Acts as a solvent

39
Q

Potassium hydroxide reacts with 2-bromo-3-methylbutane to form 3-methylbutan-2-ol
Suggest one change to the reaction conditions that would increase yield of 3-methylbutan-2-ol

A

Lower temperature/ use concentrated KOH

40
Q

Identify the characteristics of 2-bromopropane molecule that enables it to undergo a reaction with KOH to form propan-2-ol

A

C-Br bonds is polar on C atom on C-Br bond is delta positive

41
Q

Give one condition that favours the reaction elimination instead of nucleophilic substitution

A

high concentration of hydroxide

42
Q

Give a condition necessary for a high yield of an alkene when a haloalkane is converted into an alkene

A

high temperature /
ethanolic conditions

Chemistry 2.0 (9 decks)

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