Halogen derivatives

Question 1

Nucleophilic substitution reactions

Answer 1

Occur as the C-X bond attracts nucleophiles

Nucleophile donates a pair of electrons to the carbon atom bonded to the halogen

Question 2

Substitution of sodium hydroxide to bromoethane

Answer 2

Ethanol plus sodium bromide

Alcohol plus sodium halide

Question 3

Substitution of ammonia to bromoethane

Answer 3

Ethamine plus ammonium bromide

Primary amine plus ammonium halide

Question 4

Substitution of sodium cyanide to bromoethane

Answer 4

Ethanitrile plus sodium bromide

Nitrile plus sodium halide

Question 5

Elimination of haloalkanes

Answer 5

Produces a hydrogen halide as the small molecule being removed
2-bromopropane+sodium hydroxide—>propene+water+sodium bromide with HBr being eliminated

Question 6

Two mechanisms that can operate in the nucleophilic substitution reactions of haloalkanes

Answer 6

Sn1 and Sn2

Mechanism determined by the structure of the haloalkane involved in the reaction

Question 7

Sn2

Answer 7

Mechanism for primary haloalkanes
OH- donates a pair of electrons to the delta positive carbon atom forming a new covalent bond and at the same time the C-Br bond is breaking
Br atom undergoes heterolytic fission to form Br-
Rate depends on concentration of both the haloalkane and the hydroxide ions present

Question 8

Sn1

Answer 8

Mechanism for tertiary haloalkane
Reacts with OH- by two step mechanism
First step=breaking of C-Br bond to form a tertiary carbocation and a bromide ion
Breaking of C-Br bond is heterolytic fission
The C+ is then liable to attack by nucleophiles such as OH-
Rate depends on concentration of haloalkane
Tertiary haloalkanes are more stable than primary haloalkanes because they have

Question 9

Secondary haloalkanes

Answer 9

Tend to react by a mixture of the Sn mechanisms

Question 10

Flouroalkanes and flourohaloalkanes uses

Answer 10

Anaesthetics
Solvents
Refrigerants 
Aerosol propellants
Relative chemical inertness

Question 11

Chlorofluoralkanes

Answer 11

Reactive high up in the atmosphere
UV light from the sun breaks the C-Cl bonds which releases chlorine free readicals
These react with ozone molecules and leads to the depletion of the ozone layer