Halogenoalkanes Flashcards
electronegativity of carbon and halogens
carbon is δ+
halogen is δ-
nucleophile
electron pair donor
:NH3
no charge
:OH- reaction
nucleophilic substitution
produce alcohol
warm aqueous potassium or sodium hydroxide
:CN- reaction
nucleophilic substitution
heat with ethanolic potassium cyanide under reflux
:NH3 reaction
nucleophilic substitution
ethanolic ammonia + excess amonnia
heat under pressure
C-Br
C-NH3
C-NH2
nucleophilic substitution
Nu to C
C-X to X
strengths of bonds
C-F strongest, least reactive, highest bond enthalpy
Hydrolysis
CH3CH2X + H2O -> CH3CH2OH + X- + H+
Water is a poor nucleophile but it can react slowly with halogenoalkanes in a substitution reaction
Aqueous silver nitrate
added to a halogenoalkane. The halide leaving group combines with a silver ion to form a silver halide precipitate.
The precipitate only forms when the halide ion has left the halogenoalkane and so the rate of formation of the precipitate can be used to compare the reactivity of the different halogenoalkanes.
The quicker the precipitate is formed, the faster the substitution reaction and the more reactive the halogenoalkane.
AgI
yellow ppt forms fastest
AgBr
cream ppt
AgCl
white ppt forms slowest
elimination
halogenoalkane -> alkene
Reagents: Base, OH-
Potassium (or sodium) hydroxide
Conditions: In ethanol ; heat
elimination mechanism
:OH- to H
H-C to C-C
C-Br to Br
