Chapter 15 Flashcards
Haloalkanes
What is a Nucleophile?
Nucleophiles are negative ions, or molecules with a partially negative atom, that can donate a lone pair of electrons to form a new covalent bond
Which mechanism do primary haloalkanes undergo?
Nucleophilic substitution
What is hydrolysis?
Hydrolysis is a chemical reaction involving water or aqueous hydroxide ions.
What happens in the hydrolysis of a haloalkane (In simple terms)
In the hydrolysis of a haloalkane, the halogen atom is replaced by an -OH group to form an alcohol
What happens in the nucleophilic substitution of the hydrolysis of a haloalkane
- OH- ion approaches the δ+ carbon on the opposite side of the molecule from the δ- halogen atom to minimise repulsion
- A lone pair of electrons on the OH- ion is donated to the δ+ carbon atom and a new bond is formed
- The carbon-halogen bond breaks by heterolytic fission
What does the rate of hydrolysis of the haloalkanes depend on?
The strength of the carbon-halogen bond.
Iodoalkanes react the fastest (bond is weakest)
Fluoroalkanes react the slowest (C-F bond is strongest [fluoroalkanes unreactive])
The rate of hydrolysis of primary haloalkanes is measured with ethanol and aqueous silver nitrate solution. Why?
Ethanol acts as a bridging solvent since Haloalkanes are not soluble in water
The water (aqueous) acts as a nucleophile
Name uses of organohalogen compounds
Solvent for cleaning
Dry cleaning solvent
Flame retardants
Refrigerants
What are The effects of exposure to UVB radiation?
Sun Burns
Skin cancer
Genetic damage
Crop damage
What are some advantages of CFCs
stable
non-toxic
non flammable
(due to the strength of the Carbon-Halogen bonds)
What is the disadvantage of CFCs
Once they reach the stratosphere, they break down and form chlorine radicals, which act as catalysts to break down the ozone layer
What is the chlorine radical cycle?
Initiation: Formation of radicals via homolytic fission ( requires UV radiation)
CFCl3 –> CFCl2* + Cl*
Propagation: Chain reaction
Cl* + O3 –> ClO* + O2
ClO+ O –> Cl + O2
Overall equation:
O3+O –> 2O2
Name 4 alternatives to CFCs and their uses
HCFCs- breaks down more easily
HFCs- Contain no chlorine atoms but expensive
Hydrocarbons as propellants- Flammable
Pump action spray dispensers
What other natural radicals break down the ozone?
Nitrogen oxide radicals form naturally during lightning strikes
Many more radicals exist, which follow the same reaction pattern
