Chapter 15: Haloalkanes 15.1-15.2)

Question 1

general formula of a haloalkane

Answer 1

Cn H2n+1 X

X is a halogen atom

Question 2

functional group of haloalkanes

Answer 2

fluoro, -F
chloro, -Cl
bromo, -Br
iodo, -I

Question 3

polarity of haloalkanes

Answer 3

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 𝛿+ carbon atom

Question 4

what is a nucleophile

Answer 4

an atom or group of atoms that donates an electron pair to an electron-deficient centre
usually electron rich (𝛿-) and may be an negative ion (-)

Question 5

common nucleophiles

Answer 5

H20, NH3+, OH-, halogens

Question 6

strength of C-X bond and its effect on reactivity

Answer 6

C-X bond enthalpy decreases down the group

this means that iodo-, bromo-, and chloro- alkanes are the most reactive

Question 7

what happens in the nucleophilic substitution of haloalkanes

Answer 7

a nucleophile replaces the halogen in the haloalkane, which is lost as a halide ion

Question 8

which aqueous alkalis are normally used for the hydrolysis of haloalkanes

Answer 8

NaOH (aq)

KOH (aq)

Question 9

nucleophilic substitution mechanism (mechanism for hydrolysis of haloalkanes)

Answer 9

• 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

Question 10

how to make haloalkanes undergo hydrolysis with water

Answer 10

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.

Question 11

how to measure the rate of hydrolysis of different carbon-halogens

Answer 11

measuring and comparing the time for the silver-halide precipitate to form

Question 12

which halo-alkane reacts fastest

Answer 12

idoalkanes (fastest)
bromoalkanes
chloroalkanes (slowest)

Question 13

hydrolysis of haloalkanes which aqueous hydroxide ions OH- (aq)

Answer 13

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.

Question 14

What happens when you react a haloalkane with potassium cyanide and what conditions do you need?

Answer 14

C-N replaces the X and produces a nitrile and KX

Nucleophilic substitution