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Chemistry > Chapter 15 - Haloalkanes > Flashcards

Chapter 15 - Haloalkanes Flashcards

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1
Q

What are nucleophiles ?

A

Species that donate a lone pair of electrons

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2
Q

What are nucleophiles likely to have ?

A
  • A negative charge

- A lone pair of electrons

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3
Q

Give three examples of nucleophiles

A
  • OH -
  • NH3
  • H2O
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4
Q

When a haloalkane reacts with a nucleophile, what is the name of the reaction mechanism?

A

Nucleophilic substitution

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5
Q

What is hydrolysis ?

A

A chemical reaction involving water or hydroxide ions that causes the breaking of a bond in a molecule

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6
Q

Describe the nucleophilic substitution reaction for the hydrolysis of a haloalkane

A
  • OH- approaches the carbon bonded to the halogen on the opposite side to the halogen
  • This minimises repulsion between the nucleophile and halogen’s dipole
  • Lone pair of electrons on OH attracted to and donated to carbon atom
  • New bond formed betwen oxygen and carbon atom
  • Carbon-halogen bond breaks
  • Alcohol and halide ion formed
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7
Q

Describe the conditions for the hydrolysis of haloalkanes

A

Using aqueous sodium hydroxide (NaOH) and is heated under reflux

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8
Q

What determines how fast a specific carbon-halogen bond will break ?

A

Bond enthalpy

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9
Q

Which haloalkane will react the fastest and why ?

A

Iodoalkanes because the C-I bonds are the weakest so require the least amount of energy to break

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10
Q

How can hydrolysis of haloalkanes be compared to one another ?

A

Perform the reaction in the presence of aqueous silver nitrate (AgNO3) and record the time taken to form a precipitate

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11
Q

What would the result of hydrolysis of haloalkanes

show ?

A
  • Chloroalkanes react slowest
  • Iodoalkanes react fastest
  • Therefore rate of hydrolysis increases as the strength of the carbon-halogen bond decreases.
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12
Q

How does the primary, secondary or tertiary haloalkanes status affect rate of hydrolysis?

A

Tertiary reacts the fastest because the intermediary carbocation that is formed is much more stable than a primary carbocation

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13
Q

What are organohalogen compounds ?

A

These are molecules that contain at least one halogen atom joined to a carbon chain

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14
Q

What are organohalogen compounds used in ?

A
  • General solvents
  • Dry cleaning solvents
  • Making polymers
  • Flame retardants
  • Refrigerants
  • Pesticides
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15
Q

Where is the ozone layer found ?

A

10km to 40km above the earths surface

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16
Q

What is ozone (formula) ?

A

O3

17
Q

What is UV-B ?

A

Biologically damaging UV radiation

18
Q

What health conditions are UV-B linked to ?

A

Sun burn, eye cataracts, skin cancer

19
Q

What does UV - B cause ?

A

It causes depletion of the ozone layer

20
Q

What happens to the ozone in the stratosphere ?

A

In the stratosphere, the ozone is continually being formed and broken down by the action of UV radiation

21
Q

Explain the breakdown of oxygen molecules into radicals

A
  • Oxygen is broken down into oxygen radicals by UV radiation

- O2 —> 2O

22
Q

What is the next step after oxygen has been broken down ?

A
  • O2 + O —> O3, this is reversible

- In this steady state, the rate of formation of ozone is the same as the rate at which it is broken down

23
Q

What has upset this equilibrium ?

A

The use of chlorofluorocarbons (CFCs)

24
Q

Until recently, where were CFCs used ?

A
  • They were used in refrigerants, AC units and as aerosol propellants
  • This is because they are stable because of the strength of their carbon-halogen bonds within their molecules
25
Q

What happens when CFCs reach the stratosphere ?

A

Once in the stratosphere, UV radiation provides sufficient energy to break a carbon halogen bond in CFCs by homolytic fission to form halogen radicals

26
Q

What is this process called ?

A

This process is called photodissociation

27
Q

What else can be responsible for the depletion of the ozone layer ?

A

NO, nitrogen oxide

Chemistry (29 decks)

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