ORGANIC - HALOGENOALKANES

Question 1

What are halogenoalkanes

Answer 1

functional group which is a halogen atom. much more reactive than alkanes as the C in C-X bonds is e- deficient and the C-X bonds are weak

Question 2

Halogenoalkanes boiling point trend

Answer 2

Increase with
- Chain length = longer chain greater the bp
- Down the group bp increase

Question 3

Halogenoalkanes key points

Answer 3

Polar - due to permanent dipole-dipole forces
Larger molecule, more e- so stronger VdW forces

Question 4

Nucleophilic substitution - nucleophile key points

Answer 4

• A nucleophile is an electron-rich species that can donate a pair of electrons to form a covalent bond
• it will attack a positively charged carbon atom
• either negatively charged ion or contains a partially negative atom
• contains a lone pair of electrons on the electronegative atom

Question 5

Nucleophilic substitution - conditions

Answer 5

aqeous sodium or potassium hydroxide mixed with ethanol and the halogenoalkane
water is present
warm conditions
product is an alcohol

Question 6

cyanide mechanism

Answer 6

reagent = potassium cyanide
product - nitrile
= look at notes for diagram

Question 7

hydroxide mechanism

Answer 7

reagent = sodium hydroxide
product = alcohol
= notes for diagram

Question 8

ammonia mechanism

Answer 8

reagent = ammonia
product = amine
second NH3 acts as a base and removes a proton. The pair of e- in the N-H bond are transferred to the N atom (bond breaks heterolytically) leaving the final product as an amine

Question 9

what is nucleophilic elimination

Answer 9

the removal of a small molecule from organic molecule

Question 10

nucleophilic elimination key points

Answer 10

• hot, ethanoic KOH
• loses X and H from adjacent C
• forms alkene
• OH- acts as a base not a nucleophile

Question 11

nucleophilic elimination mechanism

Answer 11

notes

Question 12

uses of halogenoalkanes

Answer 12

pvc
teflon
solvents
anaesthetics

Question 13

what does ozone act as (importance)

Answer 13

Ozone in the upper atmosphere acts as chemical sunscreen absorbing a lot of UV radiation from sun - cause skin cancer and sunburj

Question 14

ozone natural reactions

Answer 14

1. O2 —> 2O(.)
2. O2 + O(.) —> O3

Question 15

What are chlorofluorocarbons

Answer 15

CFCs are:
- all H atoms replaced by either F or Cl
- used to be widely used as refrigerants (coolants)
- also in aerosols as the propellant gas
- CFCs can be very damaging to the ozone layer

Question 16

Chlorofluorocarbons radicalisations

Answer 16

• In the upper atmosphere in UV light presence the C-Cl bond within CFCs can be broken to form CL free radicals
  = CCl3F —> CCl2F(.) + Cl(.)
  These Cl(.) catalyse the breakdown of ozone
  = Cl(.) + O3 —> O2 + ClO(.)
  = ClO(.) + O3 —> 2O2 + Cl(.)
  = 2O3 —> 3O2

Question 17

Why are CFCs banned

Answer 17

Scientists demonstrated the CFCs were creating holes in the ozone layer