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A Level Chemistry > Module 4: Chapter 15 - Haloalkanes > Flashcards

Module 4: Chapter 15 - Haloalkanes Flashcards

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1
Q

What is a haloalkane?

A

Compounds containing carbon, hydrogen, and at least one halogen

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2
Q

What is a haloarene?

A

A halogen attached directly to a benzene ring

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3
Q

What is the solubility of haloalkanes?

A

Soluble in organic solvents but insoluble in water

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4
Q

Describe how nucleophilic substitution occurs in haloalkanes:

A

The nucleophile has a lone pair of electrons and the carbon-halogen bond is polar. The electrons in the lone pair move to form a bond with the slightly positive carbon atom. However, carbon is restricted to 8 electrons in its outer shell so the polar carbon halogen bond breaks heterolytically forming a negative halide ion (the leaving group).

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5
Q

What 2 types of reaction mechanisms can occur when a haloalkane reacts with an OH- ion?

A
  • Nucleophilic substitution
  • Elimination
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6
Q

What is the organic product of nucleophilic substitution between haloalkanes and OH-?

A

Alcohol

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7
Q

What is the organic product of elmination between haloalkanes and OH-?

A

Alkene

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8
Q

Why does 1-iodopropane react faster with nucleophiles than 1-chloropropane?

A

THe C-I bond is longer and therefore weaker than the C-Cl bond. Therefore, 1-iodopropane reacts faster than 1-chloropropane.

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9
Q

What is the reaction between a haloalkane and warm aqueous NaOH?

A
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10
Q

What is the mechanism between a haloalkane and warm aqueous NaOH?

A
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11
Q

What is the type of mechanism is the reaction between a haloalkane and warm aqueous NaOH?

A

Nucleophilic substitution

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12
Q

What are the conditions for the reaction between a haloalkane and NaOH?

A
  • Warm
  • aqueous
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12
Q

What is the reaction between a haloalkane and warm ethanolic KCN?

A
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13
Q

What is the mechanism between a haloalkane and warm ethanolic KCN?

A
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14
Q

What is the type of mechanism in the reaction between a haloalkane and warm ethanolic KCN?

A

Nucleophilic substitution

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15
Q

What are the conditions in the reaction between a haloalkane and KCN?

A
  • Ethanolic
  • Warm
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16
Q

What is the reaction between a haloalkane and ammonia?

A
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17
Q

What is the mechanism between a haloalkane and ammonia?

A
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18
Q

What is the type of mechanism in the reaction between a haloalkane and ammonia?

A

nucleophilic substitution

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19
Q

What are the conditions in the reaction between a haloalkane and ammonia?

A

Excess concentrated ammonia dissolved in ethanol at pressure in a sealed container

20
Q

What is the reaction between a haloalkane and hot ethanolic KOH (or NaOH)?

A
21
Q

What is the mechanism between a haloalkane and hot ethanolic KOH (or NaOH)?

A
22
Q

What is the type of mechanism in the reaction between a haloalkane and hot ethanolic KOH (or NaOH)?

A

Elimination

23
Q

What are the conditions in the reaction between a haloalkane and KOH (or NaOH)?

A
  • Hot
  • Ethanolic
24
Q

Why do haloalkanes have higher boiling points than equivalent alkanes?

A

Alkanes are non-polar molecules but haloalkanes contain a polar bond and are polar molecules. Therefore, although both contain London forces, only haloalkanes contain permanent dipole-dipole interactions. Therefore haloalkanes have a higher boiling popint than equivalent alkanes

25
Q

Why, during nucleophilic substitution in the hydrolysis of haloalkanes, does the OH- approach the carbon from the opposite side than the halogen atom?

A

This minimises the repulsion between the negative hydroxide ion and negative halogen atom

26
Q

What is a haloalkane hydrolysis reaction?

A

A nucleophilic substitution reaction in which the halogen atom is substituted for a hydroxide group.

27
Q

What is a hydrolysis reaction?

A

A reaction involving water or an aqueous solution of a hydroxide that causes the breaking of a bond in a molecule causing the molecule to be split into 2 products

28
Q

What is the trend in the strength of carbon-halogen bonds?

A

The strongest is C-F and it decreases down the group

29
Q

How would you compare the rates of hydrolysis of different carbon-halogen bonds

A

Carry out the reaction in the presense of silver nitrate. As the reaction takes palce, halide ions produced will react with silver ions to form a silver halide precipitate. Observe the time taken for the precipitate to form and compare with different haloalkanes

30
Q

What colour is the precipitate of silver chloride?

A

White precipitate (forms slowly)

31
Q

What colour is the precipitate of silver bromide?

A

Cream precipitate (forms slower than iodide but faster than chloride)

32
Q

What colour is the precipitate of silver iodide?

A

Yellow precipitate (forms rapidly)

33
Q

How does the rate of hydrolysis change depending on the halide?

A

The rate of hydrolysis increases as the strength of the carbon-halogen bond decreases (rate increases down group)

34
Q

What are organohalogen compounds?

A

Molecules that containa t elast one halogena tom joined to a carbon chain

35
Q

What are the uses of organohalogen compounds?

A
  • Pesticides
  • General solvents
  • Making polymers
  • Flame Retardants
  • Refrigerants
36
Q

What is the ozone layer and why is it important?

A

The ozone layer is found at the outer edge of the stratosphere. Only a small amount of the gases that make up this layer are actually ozone, however, this is enough to absorb most of the biologically damaging ultraviolet radiation (UV-B) from the suns rays, only allowing a small amount to reach the earths surface

37
Q

Why is UV-B damaging?

A

UV-B is damaging as it is linked to sun burn, increased genetic damage, and a greater risk of skin cancer in humans

38
Q

What is ozone?

A

O₃

39
Q

Describe what happens to ozone naturally in the stratosphere

A

Ozone is continually being formed and broken down by the action of UV light. Initially the very high energy UV breaks oxygen molecules down into oxygen radicals “O₂ -> 2O^ “. A steady state is then set up involving O₂ and the oxygen radicals in which ozone forms and then breaks down. This is in equilibrium “O₂ + O^ ⇌ O₃”

LET ^ = BULLET POINT (FOR RADICALS)

40
Q

What are CFC’s?

A

Chlorofluorocarbons

41
Q

How do CFC’s deplete the ozone layer?

Use CF₂Cl₂ as an example CFC

A

They deplete the ozone layer through a series of free radical substitution reactions:

Initiation: CF₂Cl₂ -> CF₂Cl^ + Cl^

Propogation Step 1: Cl^ + O₃ -> ClO^ + O₂
Propogation Step 2: ClO^ + O -> Cl^ + O₂

Overall equation: O₃ + O -> 2O₂

LET ^ = BULLET POINT FOR RADICALS

42
Q

What is the overall equation for the breakdown of ozone by CFC’s?

A

O₃ + O -> 2O₂

43
Q

Are CFC’s responsible for all ozone depleting reactions?

A

No, there are other harmful radicals which can also catalyse the breakdown of ozone, such as nitrogen oxide radicals

44
Q

What are the 2 propogation steps for when nitrogen oxide radicals deplete the ozone in the atmosphere?

A
45
Q

How nitrogen oxide radicals found in the environment?

A
  • formed naturally during lightning strikes
  • as a result of aircraft travel
46
Q

What is photodissociation?

A

The breakdown of a molecule by radiation

47
Q

What 2 types of radicals act as catalysts for the breakdown of ozone?

A
  • Chlorine radicals (formed from homolytic fission of CFC’s)
  • Nitrogen Oxide radicals
48
Q

What are the steps for EVERY hydrolysis reaction?

all previous examples follow this

VERY IMPORTANT

A
  1. The nucleophile OH⁻, approaches the carbon atom attached to the ahlogen on the opposite side of the molecule from the halogen atom (this direction minimises the respulsion between the nucleophile and the δ- halogen atom)
  2. A lone pair of electrons on the hydroxide ion is attracted and donated to the δ+ carbon atom
  3. A new bond is formed between the oxygen atom of the hydroxide ion and the carbon atom
  4. The carbon-halogen bond breaks by heterloytic fission
  5. The new product formed is an alcohol and a halide ion is also formed

A Level Chemistry (31 decks)

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