Topic 13: Haloalkanes Flashcards
Haloalkane
Halogen replacing H on an alkane
Free-radical substitution steps
Initiation
Propagation
Termination
Initiation
X2 —> UV light 2X○
Cl2 —> 2Cl○
Propagation
CH4 + Cl○ —> HCl(g) (misty fumes) + ○CH3 DRAW ON LEFT HAND SIDE
○CH3 + Cl2 —> CH3Cl + Cl○
Termination
Cl○ + Cl○ —> Cl2
Cl○ + ○CH3 —> CH3Cl
○CH3 + ○CH3 —> C2H6
There are more, add them i cbb atm
CFCs
Chlorofluorocarbons eg
CHClF2 —> UV light Cl○ + CHF○
Cl○ + O3 —> ClO○ + O2
ClO○ + O3 —> 2O2 + Cl○
Ozone forms layer
Homolytic fission
The process of breaking a covalent within a molecule leading to the formation of radicals
CFCs why used
Good solvents
Ozone
Protects from uv light
Nucleophilic substitution
An electron-rich nucleophile attacks a positive charge or partial positive charge to replace an atom/ group of atoms (usually attacks a haloalkane)
Nucleophile
Donates a pair of electrons to form a bond
Nucleophilic substitution mechanism
Arrow from lone pair to carbon
Arrow from bond to Bromine
Partial charges
Lone pair
Nucleophiles examples
:OH- , :-CN ALWAYS ON THE CARBON, :NH3
Created from cyanide nucleophile attacking haloalkane
Added carbon to chain
Nitrile group
e.g. propanenitrile
Ammonia nucleophile attacking haloalkane and product
Another ammonia attacks
Arrow from bond to N
Arrow from ammonia nucleophile to hydrogen
Primary Amine
Conditions for elimination
Heat under reflux
Use ethanol as solvent NO WATER
Elimination mechanism
Arrow from nucleophile to hydrogen
Arrow from that c-h bond to c-c bond
Arrow from C-br bond to BR
Cascade lighting bolt shape
Nucleophile acts as what in elimination reation
Base
Elimination with hydroxide nucleophile creates
Alkene with double bond and water
Alternative propagation reaction with haloalkane
CH3Cl + Cl○ —> ○CH2Cl + HCl
○CH2Cl + Cl2 —> CH2Cl2 + Cl○
Conditions of Nucleophilic substitution
Cold aqueous alcoholic solution
Solubility of haloalkanes
Insoluble in water - dipole-dipole forces
Boiling point of haloalkanes
Bp increases with chain length
Bp increases down group
Vdw greater - more electrons
Reactivity of haloalkanes
Increases down group
Strength of X-C bond decreases down group
Electronegativity decreases down group
