Halogenoalkanes Flashcards
Why do halogenoalkanes have polar bonds?
Because the halogens are more electronegative than carbon
What is a nucleophile?
An electron pair donor
What is an electrophile?
An electron pair acceptor
What nucleophiles can halogenoalkanes undergo substitution reactions with?
-:OH, -:CN and :NH3
What is the general mechanism for nucleophilic substitution?
The lone pair from the nucleophile goes to the δ+ C and the C-halogen bond breaks and the electrons go to the halogen
What are the reaction conditions for the nucleophilic substitution of a halogenoalkane by a hydroxide ion?
Halogenoalkane dissolved in ethanol, aqueous sodium hydroxide, gentle reflux
What is the general equation for the nucleophilic substitution of a halogenoalkane by a hydroxide ion?
R–CH2X + NaOH → R–CH2OH + NaX
What are the reaction conditions for the nucleophilic substitution of a halogenoalkane by a cyanide ion?
Halogenoalkane dissolved in ethanol, aqueous potassium cyanide, gentle reflux
What is the general equation for the nucleophilic substitution of a halogenoalkane by a cyanide ion?
R–CH2X + KCN → R–CH2CN + KX
What are the reaction conditions for the nucleophilic substitution of a halogenoalkane by an ammonia molecule?
Halogenoalkane dissolved in ethanol, excess concentrated ammonia, sealed container under pressure
What is the general equation for the nucleophilic substitution of a halogenoalkane by an ammonia molecule?
R–CH2X + 2NH3 → R–CH2NH2 + NH4X
What is mechanism for the nucleophilic substitution of a halogenoalkane by an ammonia molecule?
The lone pair on the NH3 goes to the δ+ C and the electrons from the C-halogen bond go to the halogen. The N then has a positive charge so the lone pair on another NH3 goes to one of the original NH3’s Hs and the electrons from the N-H bond go to the positive N
What does the rate of nucleophilic substitution depend on?
How easy it is to break the carbon-halogen bond
Which halogen forms the strongest bond with carbon?
Fluorine
Which halogen forms the weakest bond with carbon
Iodine
When do hydroxide ions act as a base?
When dissolved in ethanol
What do hydroxide ions do when they are acting as a base?
Accept a proton (H+)
What are the reaction conditions for the elimination of a halogenoalkane?
Halogenoalkane dissolved in ethanol, ethanolic potassium hydroxide
What is the general equation for the elimination of a halogenoalkane?
R–CH2CH2X + KOH → R–CH=CH2 + H2O + KX
What is the general mechanism for the elimination of a halogenoalkane?
The lone pair on the OH- goes to a H bonded to a C adjacent to the C-halogen, the electrons from that C-H bond goes to the C-C bond between that C and the C-halogen C and the electrons from the C-halogen bond go to the halogen
Why is ozone beneficial?
It absorbs UV radiation
What causes C-Cl bonds to break?
UV radiation
What is created when C-Cl bonds break?
Chlorine radicals
What do chlorine radicals catalyse?
Ozone depletion
What caused the hole in the ozone layer and why?
CFCs because they are stable in the lower atmosphere and diffuse into the stratosphere where they produce chlorine radicals
What are the 2 equations for the decomposition of ozone?
Cl● + O3 → ClO●+ O2
ClO●+ O3 → 2O2 + Cl●
What did governments do to stop the depletion of the ozone layer?
Banned the use of CFCs as solvents and refrigerants
What have chemists developed to replace CFCs?
Chlorine-free alternatives
