Chapter 15 Flashcards
(19 cards)
Describe the carbon-halogen bond
Polar
Halegens more electronegative then carbon
3 nucleophilles that react with haloalkanes
OH-
CN-
NH3
How do you get from haloalkane to alcohol
Name of mechanism
Conditions
Nucleophillic substitution
Warm aqueous alkali eg sodium hydroxide
Describe the mechanism for nucleophillic substitution
OH- is nucleophile which provides a pair of electrons for the c delta +
The C-Br bond breaks hetrolytically - both electrons taken by Br
BR- falls off as OH- bonds to carbon
Drawing:
Arrow from unbonded pair to C
Arrow from middle of C-Br bond to Br
Br ends up with lone pair
Water + haloalkane
Eventually get an alcohol as water is a weak nucleophile
Products would be alcohol H+ amd Br-
Which haloalkane hydrolyses quickest and slowest
Iodoalkanes hydrolyse fastest as they have the smallest bond enthalpies, so weakest bonds
Fluoroalkanes hydrolyse the slowest as the have the largest bond enthalpies so strongest bonds
Experiment to compare the reactivity of haloalkanes
Haloalkane + water to make alcohol
Add silver nitrate solution to react with the halide ions as they form, forming a ppt
Add Ethan’s as a solvent and use water bath
What are CFCs
Chlorofluorocarbons
Do not contain ash hydrogen atoms only chlorine fluorine and carbon
Properties of CFCs and uses
Stable, volatile, non flammable and non toxic
Fridges, aerosol cans, air con
What is the ozone
How is it formed
Upper atmosphere that absorbs a lot of UV
Formed naturally when an oxygen molecule is broken down into 2 free radicals by UV. The free radicals attack oxygen molecules forming ozone
Equation for formation of ozone
O2—UV—> O +O
O2 + O——> O3
How are holes in the atmosphere formed
CFCs absorb UV amd split to form chlorine radicals which catalyse the destruction of ozone
They destroy ozone then are regenerated to destroy ozone again
Radical substitution for the destruction of ozone
Cl. + O3—-> O2 + ClO.
ClO. +O —-> O2+Cl.
Overall reaction
O3+O—-> 2O2
What free radicals from nitrogen oxides are formed and what are their effect
NO. Produced from engines amd thunderstorms amd effect in the same way as chlorine
When were CFCs banned
1970s
What was the Montreal Protocol
1989
International treaty to phase out use if CFCs
Alternatives to CFCs
HCFCs (hydrochlorofluorocarbons) HFCs (hydrofluorocarbons) both green house gases
HCFCs
Broken down in atmosphere in 10-20 years
Still damage ozone layer but smaller effect then CFCs
HFCs
Broken down in atmosphere but don’t contain chlorine so don’t effect ozone layer
