Halogenoalkanes Flashcards
(28 cards)
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
