Organic 3 Haloalkanes

Question 1

Haloalkane➡️alcohol
Reagent
Type and mechanism

Answer 1

Aqueous potassium hydroxide
Reflux
Nucleophilic substitution

Question 2

Mechanism for haloalkane ➡️alcohol

Answer 2

Permanent dipole across C-X bond
Lone pair on OH- attracted to delta +C so curly arrow from lone pair to this C
Heterolytic fission of C-X bond
Alcohol and halide ion produced

Question 3

Haloalkane➡️nitriles
Reagent
Conditions
Type and mechanism

Answer 3

Potassium cyanide (alc)
Nucleophilic substitution
Reflux
Lone pair on CN- attracted to delta + C on haloalkane
Length of carbon chain increases by 1

Question 4

Nitrile group

Answer 4

CN triple bond

Question 5

Haloalkane ➡️primary amine
Reagent
Conditions
Type and mechanism

Answer 5

Ammonia (excess concentrated and alc)
Warm
Nucleophilic substitution

Question 6

Mechanism for haloalkane➡️primary amine

Answer 6

Permanent dipole across C-X
Lone pair on ammonia attracted to the delta positive carbon
Heterolytic fission of C-X bond
Positive charge in N/ electron deficient
N more electronegative than H
Another ammonia lone pair attracted to H
Heterolytic fission of N-H bond
Primary amine produced
NH3 acts as a base
NH4+ and X- also produced (ammonium ion salt)

Question 7

Haloalkane➡️Alkene
Reagent
Conditions
Type and mechanism

Answer 7

Ethanolic potassium hydroxide
Reflux
Elimination
Hydroxide ions acting as a base to remove H+ ion from haloalkane
Neutralises the reaction to produce water
1. Lone pair on OH- attracted to the H on the C next to the C-X bond
2. Bond between OH and H forms causing C-H bond to break causing a C=C
3. Causes C-X to break by Heterolytic fission as most difference in electronegativity
4. Alkene
Isometric products

Question 8

Haloalkane➡️alcohol
Reacting with water then adding silver nitrate (aq) ?

Answer 8

React with water
Silver ions react with halide ions as soon as they form from the above reaction
Silver halide precipitate

Haloalkane dissolved in ethanol reacted with silver nitrate solution (contains the water)

Question 9

Trend in reactivity of the haloalkanes in terms of bond enthalpy

Answer 9

Iodoalkanes are the most reactive
Because they have the lowest bond enthalpy so are easier to substitute
This is because iodine is the larger halogen so the bond is longer

Question 10

Comparing relative rates of hydrolysis of chloro bromo and iodo alkanes

Answer 10

3 test tubes containing ethanol (solvent) and silver nitrate solution (contains the water). Add different haloalkane to each and time how long it takes for a silver halide precipitate to form
Silver iodide would form the fastest
The substitution forms an alcohol and releases a halide ion which immediately form a precipitate with a silver ion

Question 11

Comparing relative rates of hydrolysis of primary secondary and tertiary haloalkanes

Answer 11

3 test tubes containing ethanol and silver nitrate solution
Add a primary type of haloalkane (either bromo iodo or chloro) to one, secondary to other (same type) and tertiary to the last (same type)
Time how long it takes for precipitate to form

Question 12

Reflux reactions

Answer 12

With KOH(aq)