Chapter 15: Haloalkanes 15.1-15.2) Flashcards
general formula of a haloalkane
Cn H2n+1 X
X is a halogen atom
functional group of haloalkanes
fluoro, -F
chloro, -Cl
bromo, -Br
iodo, -I
polarity of haloalkanes
C-X is a polar bond (halogens more electronegative than carbon)
C-X bond polarity decreases down the group because the electronegativity of halogens decree from F -> I
Polarity of the C-X bond attracts nucleophiles to the Cd+ atom
what is a nucleophile
an atom or group of atoms that donates an electron pair to an electron-deficient centre
usually electron rich and may be an negative ion
common nucleophiles
H20, NH3+, OH-, halogens
strength of C-X bond and its effect on reactivity
C-X bond enthalpy decreases down the group
this means that iodo-, bromo-, and chloro- alkanes are the most reactive
what happens in the nucleophilic substitution of haloalkanes
a nucleophile replaces the halogen in the haloalkane, which is lost as a halide ion
which aqueous alkalis are normally used for the hydrolysis of haloalkanes
NaOH (aq)
KOH (aq)
nucleophilic substitution mechanism (mechanism for hydrolysis of haloalkanes)
- the OH- ion acts as a nucleophile, donating an electron pair to the d+ carbon atom
- OH-nion attacks from the opposite side to the halide as to reduce repulsion
- a new bond forms between the oxygen atom of the OH- ion and the carbon atom
- the carbon-halogen bond breaks by heterolytic fission
- an alcohol and a halide ion are formed
how to make haloalkanes undergo hydrolysis with water
haloalkanes do not dissolve in water
however in the presence of an ethanol solvent and aqueous silver nitrate, water acts as a nucleophile to form alcohol.
how to measure the rate of hydrolysis of different carbon-halogens
measuring and comparing the time for the silver-halide precipitate to form
which halo-alkane reacts fastest
idoalkanes (fastest)
bromoalkanes
chloroalkanes (slowest)
hydrolysis of haloalkanes which aqueous hydroxide ions OH- (aq)
hydroxide, OH-, ions are nucleophiles with a lone pair of electrons on the oxygen atoms, which can be donated to from a new covalent bond.
haloalkanes undergo nucleophilic substitution reactions with aqueous alkali, OH- (aq), to form alcohols.
What happens when you react a haloalkane with potassium cyanide and what conditions do you need?
C-N replaces the X and produces a nitrile and KX
Nucleophilic substitution