15.1 - 15.2 Flashcards

1
Q

What are halogenoalkanes

A
  • alkanes with 1 or more halogen attached to it
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2
Q

What do all haloalkanes have and why

A
  • a polar bond as they have halogen attached to them
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3
Q

What are haloalkanes attacked by

A
  • nucleophiles
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4
Q

Why do haloalkanes have polar bonds

A
  • as halogens are more electronegative than carbon so they pull electrons towards themselves in a covalent bond
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5
Q

What is a nucleophile

A
  • a electron pair donor that forms a new covalent bond
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6
Q

What are 4 examples of nucleophiles

A

1) NH3 (ammonia)
2) CN- (cyanide ions)
3) OH- (hydroxide ions)
4) H2O (water)

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7
Q

What do curly arrows show

A
  • the movement of electron pairs
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8
Q

Where does the arrow start from and go to with nucleophiles

A
  • starts from the lone pair on the nucleophile
  • goes to the carbon atom
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9
Q

What reaction do haloalkanes undergo

A
  • nucleophilic substitution
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10
Q

How do haloalkanes form alcohols

A
  • nucleophilic substitution
    REAGENT: warm NaOH
  • carried out under REFLUX
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11
Q

In nucleophilic substitution the what type of bond fission happens when the bond between the carbon and the halogen break

A
  • heterolytic bond fission as both electron move to form the bond to the halogen
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12
Q

Is water a weak or strong nucleophile, and what affect does this have not he reaction

A
  • weak so it is slower
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13
Q

What is the reactivity of haloalkanes

A
  • they become more reactive as we go down the group and hydrolysed (breaking the C-HALOGEN bond)the fastest
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14
Q

What determines reactivity of haloalkanes

A
  • bond strength
  • bond enthalpy
    NOT THE BOND POLARITY
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15
Q

How do we test for which haloalkane is which and what results should we get

A

1) Place chloroalkane, bromolakane and iodoalkane into 3 test tubes
2) add silver nitrate solution and ethanol (solvent) to each tube

RESULTS:
- iodoalkanes will form a yellow precipitate first as it has the weakest bond enthalpy so is more reactive
- bromoalkane will form a cream precipitate second
- chloroalkane will form a white precipitate last as it has the highest bond enthalpy and so is less reactive

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16
Q

What are CFCs

A
  • chlorofluorocarbons
  • they have all their hydrogens replaces by chlorine and fluorine
  • stable molecules but are broken down by UV)
17
Q

What do CFCs do

A
  • break down ozone (O3) in the atmosphere
18
Q

How are the C-Cl bond in CFCs broken and what does it form

A
  • by UV radiation in the atmosphere
  • which forms radicals
19
Q

What catalyses the break down of ozone

A
  • the radical formed when the C-Cl bonds are broken by UV radiation
20
Q

Why is a C-Cl bond more likely to be broken in CFCs compared to a C-F bond

A
  • as C-Cl bonds have a lower bond enthalpy so not a lot of energy is needed to break the bond
21
Q

Write the free radical substitution reaction for CFCs

A

Initiation:
UV
CCl3F(g) ——> . CCl2F(g) + Cl .(g)

Propagation:
1) Cl .(g) + O3(g) —> O2(g) + ClO .(g)
2) ClO .(g) + O3(g) —> 2O2(g) + Cl .(g)

Termination:
Cl .(g) + Cl .(g) —> Cl2(g)

22
Q

What is the overall equation in the breakdown of the ozone and what is the catalyst

A

2O3(g) —> 3O2 (g)
* Cl . Is the catalyst

23
Q

What are other radicals that destroy ozone

A
  • Nitrogen oxides
24
Q

True or false:
CFCs are now banned

25
Why do we need to ozone layer
- as it absorbs most harmful UV radiation that causes skin cancer
26
What are alternative to CFCs
- HFCs (hydrofluorocarbon)=> beneficial as it doesn’t have the chlorine which would from radicals to break down the ozone layer
27
How do we know that the alternative HFCs and other alternatives are working
- because the holes in the ozone layer are slowly becoming smaller