Haloalkanes Flashcards
What decides if a haloalkane is primary, secondary or tertiary?
The number of carbon atoms directly bonded to the halogen carbon
Why are carbon halogen bonds polar?
Higher electronegative halogen compared to C
How do haloalkanes react with nucleophiles?
Due to the difference in electronegativity they under nucleophillic substitution reactions.
What is a nucleophile?
An electron pair donor
How do haloalkanes make alcohols?
React with water (slowly) or aqueous hydroxide ions (NaOH) more quickly = hydrolysis
RX + H20 —> ROH + HX
RX + NaOH —> NaX
Describe the process of comparing rates of hydrolysis of Haloalkanes.
RX + H20 —> ROH + H+ + X-
The water for the reaction is aq of AgNO3 (aq)
- Use haloalkanes with same chain length
- In one test tube add ethanol and haloalkane
- In another test tube add silver nitrate solution
- Place both in 50 degrees water bath
- Wait some minutes for them to come to temperature then mix.
- Measure time for precipitate to form.
- Repeat using same volumes of other haloalkanes
- Rate - 1/time
Why are the rates of hydrolysis of different haloalkanes different?
Strength of halogen bond determines rate. C-Cl has highest bond enthalpy = slowest rate. C-I bond has weakest bond enthalpy = fastest rate
What are the properties of haloalkanes?
Volatile, non-flammable, unreactive and non-toxic
What are the uses and issues of haloalkanes?
Used in past as solvents, flame retardants, aerosol propellants and refrigerants
It was found they contributed to ozone depletion. Banned by many countries in Montreal protocol. Ozone recovering but still concerns due to haloalkanes being still in environment (long residence time due to lack of reactivity) and not all countries signed up to the protocol
What is the reaction of haloalkanes in the stratosphere?
CF2Cl2 —> Cl. +CF2Cl. (via U.V. making free radicals
O3 + Cl. —> O2 + ClO.
ClO. + O —> O2 + Cl.
Overall:
O3 + 0 —> 2O2
The chlorine radical acts as a catalyst as it is reformed, free to attack more ozone molecules.
