CHAPTER 15 - HALOALKANES Flashcards
How are haloalkanes classed?
Primary, secondary and tertiary
(same premise as alcohols)
What type of reaction does haloalkanes undergo and why
Nucleophilic substitution
Negative Halide causes positive carbon, attracts negative nucleophile
What nucleophiles are common in reactions with haloalkanes
Hydroxide ions (:OH-)
Water Molecules (H2O:)
Ammonia Molecules (:NH3)
How does a hydrolysis reaction work?
OH- ions from water attack opposite side of carbon than halogen
Minimises repulsion
New bond is formed
Carbon - Halogen bond breaks through heterolytic fission
Alcohol is formed, plus halide ion
(mechanism pg 231)
What halide forms the strongest bond with carbon, then down to the weakest
Fluorine
Chlorine
Bromine
Iodine
Describe a practical to measure the rate of hydrolysis of primary haloalkanes
Add ethanol to 3 test tubes
add 2 drops of a haloalkane to each(chloro-, bromo- and iodo- butanes)
Stand in water bath at 60 degrees
Place test tube contains 0.1mol dm3 Silver nitrate into the same water bath and allow all tubes to reach the same temperature
Add AgNO3 to each test tube and start clock
Observe test tubes for 5 mins and time how long it takes for Ppts to for
Chlorine - White ppt slow
Bromine - Cream ppt, middle
Iodine - Yellow ppt forms rapidly
Explain why chlorobutane reacts the slowest with AgNO3 and iodobutane is the fastest
C-Cl bond is the strongest
C-I bond is the weakest
What is the relative reaction rates of the different classes of haloalkanes undergoing hydrolysis
Primary slowest
Secondary
Tertiary Fastest
Referring to Markownikoffs rule, explain why a tertiary carbocation is more stable than a primary carbocation
Alkyl groups reduce the charge on the carbocation by pushing electrons towards the positively charged ion
The more R-groups directly attached to the positively charged carbon in the carbocation, the more stable it is.
A tertiary carbocation has 3 alkyl groups directly attached to the positive carbon atom, but a primary carbocation has only one alkyl group
Explain why a carbon-halogen bond is polar
Halogen atoms are more electronegative than carbon atoms.
The electrons in the C-Hal bond are attracted towards the halogen making the bond polar
What is an organohalogen compounds
Molecules that contain at least one halogen atom joined to a carbon chain
What are organohalogen mostly used in
Pesticides, Solvents, making polymers, flame retardants, refrigerants
Why are organohalogens now seen as a concern?
Not found in nature
Not broken down naturally
Where is the ozone layer found?
Outer edge of stratosphere - 10 to 40 km above earths surface
What does the ozone layer do?
Absorb biologically damaging ultraviolet radiation (UV-B) from suns rays so small amounts reach surface
