3O- Halogenoalkanes Flashcards
Why do halogenoalkanes contain a polar bond
Halogen has a higher electronegativity than the carbon creating a s+ and s- side
Why does the carbon to halogen bond enthalpy influence rate of reaction
Carbon to fluorine bond, electrons have strong attraction to fluorine nucleus, strong bond, less reactive
Carbon to iodine bond, electrons have a weak attraction to iodine nucleus, weak bond, more reactive
In mechanisms how are the formation of covalent bonds shown
A curly arrow starting from a lone pair/ another covalent bond
How is the breaking of a covalent bond shown
Curly arrow starting from the bond that is being broken to the ion about o be formed
What are nucleophiles
A negative ion or an atom with a s- charge
Donates a lone pair of electrons to form a covalent bond
How to show a molecule being substituted into a mechanism
Curly arrow from electrons to atom it will form the bond with
General equation for nucleophilic substitution of halogenoalkanes with OH-
R-X + OH- —> ROH + X-
General equation for nucleophillic substitution for halogenoalkane and CN- ion
R-X + CN- —> R-CN + X-
Equation of nucleophillic substitution of halogenoalkane with 2 mol of NH3
R-X + 2NH3 —> R-NH3 + X- + NH3 —> R-NH2 + X- + NH4+
What’s ozone
A layer formed naturally in the upper atmosphere, absorbs uv radiation
How is C-Cl bond in chlorofluorocarbons broken and what happens
UV radiation breaks the C-Cl bond producing chlorine atoms
Why are chlorine atoms in the atmosphere bad
Catalyse decomposition of ozone contributing to a hole in the ozone layer
What are some uses of CFC’s that are now banned
Solvents
Refrigerants
How do chlorine atoms catalyse the decomposition of ozone (free radical substitution)
Initiation- CF2Cl2 —> CF2Cl• + Cl• (in uv light)
Cl• + O3 —> ClO• + O2
ClO• + O3 —> 2O2 + Cl•
Overall- O3 + O —> 2O2
Cl• free radical regenerates for the next reaction being able to destroy thousands of ozone molecules
NO also catalyses decomposition of ozone
What are alternative chlorine free compounds which have been developed
HFC’s hydro fluoro carbons, no C-Cl
Conditions for nucleophilic substitution with OH- ions
Dissolved in ethanol and heat
Conditions for nucleophilic substitution with cyanide ions
Ion dissolved in ethanol/water
Heat under reflux
Conditions for nucleophilic substitution with ammonia
Ammonia dissolved in ethanol
Heat under pressure
Excess ammonia
Formula of ozone
O3
What does base elimination go from and to
Halogenoalkane to alkene
Conditions for base elimination
anhydrous conditions [absence of water/H2O]
high temperature
KOH aqueous in ethanol
Mechanism for base elimination
First arrow: from the middle of the lone pair on the nucleophile to a hydrogen which is joined to a carbon which is adjacent to the carbon with the halogen.
Second arrow: From the CH bond to the CC bond
Third arrow: from the middle of the carbon halogen bond onto the halogen breaking the halogen off.
