Organic (Y1) Halogenoalkanes

Question 1

How are halogenoalkanes named?

Answer 1

Based on original alkane with prefix indicated halogen atom e,g, F; Fluoro
Cl; Chloro etc.
- substituents are listed alphabetically

Question 2

What type of reactions do halogenoalkanes undergo?

Answer 2

They undergo either substitution or elimination reactions

Question 3

What’s nucleophilic substitution?

Answer 3

Substitution: swapping a halogen atom for another atom or groups of atoms.
Nucleophile: Electron pair donator e.g. :OH- or :NH3 or CN-

Question 4

What’s the general mechanism for nucleophilic substitution

Answer 4

• Arrow from lone pair of electrons on the nucleophile to the delta positive carbon
• Arrow from C-X bond to the X
• X- is formed
  :Nu acts as nucleophile - always a lone pair.

Question 5

what is the rate of the substitution reactions dependant on?

Answer 5

The rete of these substitution reactions depends on the strength of the C-X bond. Weaker the bond is, the easier it is to break and the faster the reaction. Iodoalkanes are fastest to substitute and the fluoroalkanes are the slowest.

Question 6

Define hydrolysis

Answer 6

Hydrolysis is defined as the splitting of a molecule (in this case a halogenoalkane) by the reaction with water.

Question 7

What is formed when silver nitrate is added to a halogenoalkane?

Answer 7

Aqueous silver nitrate is added to halogenoalkane. The halide leaving group combines with a silver ion to form a silver halide precipitate.

Question 8

What colour precipitate is AgI, AgBr and AgCl respectively?

Answer 8

yellow, cream, white.

Question 9

Suggest reagent, conditions, mechanism and type of mechanism for nucleophilic substitution with hydroxide ions

Answer 9

Reagent: KOH/ NaOH
Conditions: - In aqueous solution, heated under reflux
Mechanism: Nucleophilic substitution
Type of reagent: Nucleophile.

Question 10

What is different for nucleophilic substitution for tertiary halogenoalkanes?

Answer 10

The halogen breaks off first leaving a positive carbon ( make sure to draw +) which is attacked by nucleophile.

Question 11

Suggest functional group, reagent, conditions, mechanism and type of reagent for nucleophilic substitution reaction with cyanide ions

Answer 11

Halogenoalkane --> Nitrile
Reagent: KCN dissolved in ETHANOL/Water mixt.
Conditions: Heated by reflux
Mechanism: Nucleophilic substitution
Type of reagent: Nucleophile :CN-

Question 12

Suggest reagent, conditions, mechanism, type of reagent for reaction who’s functional group changes from halogenoalkane to amine

Answer 12

Reagent: NH3 dissolved in ethanol
Conditions: Heating under pressure.
Mechanism: Nucleophilic substitution
Type of reagent: Nucleophile, :NH3

Question 13

What difference does it make if aqueous/alcoholic solvent is used to dissolve hydroxide ions

Answer 13

Aqueous: Substitution
Alcoholic: Elimination

Question 14

What’s the type of mechanism that can make the functional group change from halogenoalkane to alkene?

Answer 14

Elimination with alcoholic hydroxide ions.

Question 15

Suggest reagent, conditions, mechanism and type of reagent for elimination with alcoholic hydroxide ions.

Answer 15

Reagents: KOH/NaOH
Mechanism: Elimination
Type of Reagent: Base, OH-

Question 16

Suggest a mechanism for elimination reaction of 2-bromopropane with KOH (Alc)

Answer 16

:OH- attacks adjacent H.
The same C-H bond arrow from the bond to C-C bond adjacent.
Arrow from C-Br bond to Br.

Question 17

How can different structural isomers be formed?

Answer 17

Unsymmetrical secondary and tertiary HAs two different structural isomers can be formed.

Question 18

When 2-methyl-2-chlorobutane is eliminated, what 2 isomers can form?

Answer 18

2-methylbut-1-ene

2-methylbut-2-ene

Question 19

The structure of halogenoalkane has effect on which degree substitution/elimination occurs in the reaction. What does primary and tertiary tend towards.

Answer 19

Primary tends towards substitution. Tertiary tends towards elimination.

Question 20

Name one use of HA

Answer 20

• Chloroalkanes and chlorofluoroalkanes can be used as solvents.
• often used as refrigerants, pesticides and aerosol propellants

Question 21

Why have many uses of HA stopped?

Answer 21

Stopped due to toxicity and detrimental effect on the atmosphere.

Question 22

This is the point I gave up making questions on Ozone chemistry

Answer 22

Please learn ozone chemistry. Ok cool thanks.