Haloalkanes

Question 1

In an elimination mechanism, what does the -OH act as?

Answer 1

Base (proton acceptor)

Question 2

Elimination mechanism with 2-bromopropane to an alkene?

Answer 2

https://www.chemguide.co.uk/mechanisms/elim/elim.html

Question 3

Why are there different rates of hydrolysis?

Answer 3

As the bond enthalpy decreases, it is easier to break the C—Halogen bond so rate of reaction increases

Question 4

What is the method for testing the rate of substitution (hydrolysis) with haloalkane? (5)

Answer 4

1) Place measured sample of each haloalkane into separate test tubes
2) Place in water bath at 50 degrees
3) Into another test tube, place ethanol, water + aqueous silver nitrate in water bath
4) Once equal temperature, add equal volumes of ethanol mixture + haloalkane together
5) Time how long it takes for precipitate to form

Question 5

Nucleophilic substitution of ammonia with bromoethane?

Answer 5

https://www.scienceskool.co.uk/mechanisms-of-haloalkanes.html

Question 6

What are the following for elimination to alkene:

• Reagent
• Conditions

Answer 6

• NaOH, KOH
• Hot ethanolic + concentrated solvent

Question 7

What are the following for nucleophillic substitution for NH3:

• Reagent
• Conditions
• Type of product

Answer 7

• NH3 (ammonia)
• Excess ammonia (high heat + pressure)
• Amine

Question 8

Nucleophillic substitution by CN- (nitrile/cyanide) with bromomethane?

Answer 8

https://www.scienceskool.co.uk/mechanisms-of-haloalkanes.html

Question 9

For nucleophillic substitution by CN-, what is the:

• Reagent
• Conditions
• Type of product

Answer 9

• KCN
• Aqueous + ethanolic solvent
• Nitrile

Question 10

With nucleophilic substitution by -OH to alcohol, what is the:

• Reagent
• Conditions

Answer 10

• NaOH or KOH
• Aqueous solvent

Question 11

Nucleophilic subsitution by -OH with bromoethane to alcohol?

Answer 11

https://www.scienceskool.co.uk/mechanisms-of-haloalkanes.html

Question 12

What do curly arrows show?

Answer 12

Show the movement of a pair of electrons

Question 13

Why are CFCs damagaging to the ozone layer?

Answer 13

Cl. is regenerated in the final propagation step which causes a chain reaction in decompostion of the ozone

Question 14

Explain why CF3CH3 doesn’t lead to the depletion of the ozone? (2)

Answer 14

• Doesn’t contain Cl
• C—-F bonds are strong + don’t break

Question 15

Write 3 equations to show how CCl3F is involved in damaging the ozone layer?

Answer 15

INITIATION: CCl3F —–> Cl. + .CCl2F

PROPAGATION: Cl. + O3 —–> .ClO + O2
.ClO + O3 —–> 2O2 + Cl.

Question 16

Free-radical subsitution reaction between methane + chlorine?

Answer 16

INITIATION —–> Cl2 –-U.V–> 2Cl∙

PROPOGATION —–> Cl∙ + CH4–> ∙CH3 + HCl

          -----> ∙CH3 + Cl2--> CH3Cl + Cl∙

TERMINATION —–>Cl∙ + ∙CH3 –> CH3Cl

         -----> ∙CH3 + ∙CH3 --> C2H6

            -----> Cl∙ + Cl∙ --> Cl2

Question 17

Description of termination in free-radical substitution?

Answer 17

• TERMINATION - 2 free-radicals combine

Question 18

Description of propogation in free-radical substitution? (2)

Answer 18

STEP 1 - free-radical produced takes a H from alkane, which turns into free-radical + produces a hydrogen halide

STEP 2 - alykyl radical produced takes halogen atom from molecule, which forms haloalkane and Cl. acts as a catalyst

Question 19

Description of initiation in free-radical substitution?

Answer 19

INITITATION - halogen molecule splits into 2 free-radicals, breaking the halogen—halogen bond called homolytic fission

Question 20

What is a free-radical?

Conditions for free-radical substitution?

Answer 20

A species with an unpaired electron (very reactive)

UV light - provides energy required to break halogen—halogen bond + start reaction

Question 21

How can haloalkanes be classified? (3)

Answer 21

• Primary - C atom bonded to halogen which is only bonded to 1 other C
• Secondary - C atom bonded to halogen which is bonded to 2 other C
• Tertiary - C atom bonded to halogen which is bonded to 3 other C