3.3.3 Halogenoalkanes

Question 1

What are the conditions of nucleophilic substitution?

Answer 1

Aqueous, dilute NaOH/KOH, low temperature

Question 2

What are the conditions of elimination?

Answer 2

Ethanolic, concentrated NaOH/KOH, higher temperature

Question 3

Why are halogenoalkanes immiscible with water?

Answer 3

Bonds are not polar enough

Question 4

How would the boiling point vary between an alkane and a halogenoalkane of the same Mr?

Answer 4

The halogenoalkane would have the higher boiling point.

The C-X bond is polar which means it makes a permanent dipole dipole and van der Waals

Whereas the alkane only for van der Waals

Question 5

How does the boiling point change down Group 7 as a halogenoalkane?

What is normally expected

Answer 5

The boiling point would increase

. Increased van der Waals forces between molecules as there is a higher Mr which means more electrons

. It is expected to decrease down the group as the polarity decreases down Group 7,
. However the stronger Van der Waals outweigh this

Question 6

What is more reactive between C-I and C-F

Answer 6

C-I as it has less bond enthalpy

Question 7

What is the equation for free radicals substitution?

Answer 7

Alkane + halogen -> halogenoalkane + hydrogen Halide

In presence of UV light

Question 8

How does CFCs deplete ozone?

Answer 8

. Ozone is made naturally when O2 absorbs UV
. CFCs break up to form chlorine radicals

. Chlorine radicals then react with ozone
. Chlorine radicals regenerated (catalyst)

Question 9

Why is a C-X bond polar?

Answer 9

The halogen is more electronegative than carbon.
. Halogens have a partially negative charge and carbon has a partially positive charge