Module 4: Chapter 15 (Haloalkanes) Flashcards Preview

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Flashcards in Module 4: Chapter 15 (Haloalkanes) Deck (12)
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1

What are haloalkanes?

- haloalkanes are compounds with one or more halogen atoms attached to a hydrocarbon chain
- they are useful
- the halogen causes the relatively unreactive carbon chain to become more reactive

2

What is a nucleophile?

a species that can donate a pair of electrons

3

What are some common nucleophiles?

:OH-, H2O: and :NH3

4

Describe the reactivity of haloalkanes?

- halogen atoms are more electronegative than carbon atoms, the carbon-halogen bond is polar
- the partial positive carbon dipole attracts nucleophiles
- a dative covalent bond is formed
- nucleophile replaces/substitutes the halogen
- the mechanism is nucleophilic substitution

5

Describe the hydrolysis of haloalkanes?

- Reaction in which water/OH-(aq) causes the breaking of a bond in a molecule
- Haloalkane hydrolysis results in a halogen atom being replaced by a hydroxyl group (alcohol formed)
- this is nucleophilic substitution

Conditions:
- Reactants = aqueous sodium hydroxide and haloalkane
- heat under reflux

6

What are organhalogen compounds?

Molecules that contain at least one halogen atom joined to a carbon chain

7

What are the uses of organhalogens?

solvents for cleaning (CHCl3)
dry cleaning solvents (C2HCl2)
making polymers (C2F4)
flame retardants (CF3Br)
refrigerants (F2CCl2)

8

What is the ozone (O3) layer?

- ozone absorbs the biologically damaging UV-B from the Sun
- exposure to UVB causes sun burn and long term effects such as skin care and genetic damage
- located at the top of the stratosphere

9

Describe the ozone as a steady state?

- O2 molecules in the atmosphere absorb UV radiation. The bonds in oxygen molecules break homolytically and produce radicals (O2 -> 2O)
- These radicals are a highly reactive species that contains a single unpaired electron
- Oxygen radical combines with an O2 molecule to make ozone O3
- Ozone absorbs UV radiation and breaks back into oxygen molecules and oxygen radicals
- As these 2 processes happen at the same rate a steady state is created

10

What is happening to the ozone layer?

Human activity, especially the production and use of CFC’s has upset this delicate equilibrium.
- CFCs have a long residency time in the atmosphere

11

What is the photodissociation of CF2Cl2?

Initiation: CF2Cl2 -> CF2Cl· + Cl·
- UV radiation supplies enough energy to break carbon-halogen bonds by homolytic fission forming radicals

Propagation:
Cl· + O3 -> ClO· + O2
ClO· + O -> Cl· + O2

Overall equation:
O3 + O -> 2O2

12

What is the propagation steps for nitrogen oxides?

Propagation steps:
NO· + O3 -> NO2· + O2
NO2· + O -> NO· + O2

Overall equation:
O3 + O -> 2O2