Halogenoalkanes (Organic) (complete)

Question 1

Describe Free Radical Substitution.
Name the three steps in Free Radical Substitution.

Answer 1

• Where the Hydrogen atoms in an organic molecule are replaced halogen atoms.
  1 - Initiation - when exposed to ultraviolet light, a halogen molecule breaks apart into its two atoms, (free radicals)
  2 - Propagation - step 1: the alkane/halogenoalkane reacts with the free radical halogen, this removes a H atom from the alkane/halogenoalkane, this produces HF/HCl/HBr/HI and a carbon based free radical compound — step 2: the carbon based free radical compound reacts with a halogen molecule to place a single atom of the halogen onto the c based radical, this also produces another halogen free radical to continue the chain reaction in step 1.
  3 - Termination - If two free radicals collide, they will form a molecule and stop the chain reaction. Any two molecules involved in the mechanism could collide in this way.

Question 2

Define:
- Electrophile
- Nucleophile

Answer 2

• Electrophile - A lone pair acceptor.
• Nucleophile - A lone pair donor.

Question 3

What halogenoalkane reaction will occur with warm, aqueous NaOH?

Answer 3

• Nucleophilic substitution.
  1 - Curly arrow from the OH- lone pair to the carbon atom with the halogen attached.
  2 - Curly arrow from the C—X bond to the X atom.

Question 4

What halogenoalkane reaction will occur with ethanolic, warm KCN?

Answer 4

• Nucleophilic Substitution.
  1 - Curly arrow from CN- lone pair to C atom with halogen attached.
  2 - Curly arrow from C—X bond to X atom.

Question 5

What halogenoalkane reaction will occur with excess concentrated ammonia dissolved in ethanol?

Answer 5

• Nucleophilic Substitution.
  Sketch 1:
  1 - Curly arrow from NH3 lone pair to carbon atom with halogen atom attached.
  2 - Curly arrow from C—X bond to X atom.
  Sketch 2:
  1 - Curly arrow from NH bond (in NH3 group on carbon chain) to N+ ion. (intermediate structure)
  Sketch 3:
  2 - H+ ion drops off from N+ ion, to form amine group attached to carbon chain + H+ ion.

Question 6

What halogenoalkane reaction occurs with hot, ethanolic KOH?

Answer 6

• Elimination.
  1 - Curly arrow from OH- lone pair to H atom attached to the carbon adjacent to the carbon with the halogen attached.
  2 - Curly arrow from C—H bond in step 1 to C—C bond between the two carbon atoms involved in the elimination, (forms C=C bond in centre carbon chain).
  3 - Curly arrow from C—X bond to X atom.

Question 7

How does the Ozone layer protect us from the Sun?

Answer 7

• The Ozone (O3) absorbs UV radiation preventing damage to DNA and reducing the risk of Skin Cancer.

Question 8

How does CFCs damage the Ozone layer?

(What other …monoxide can catalyse this reaction like CFCs?)

Answer 8

• CFC molecules are very inert, so only UV radiation is able to break them apart.
• They migrate into the Ozone layer, breaking apart into very reactive free radicals chlorines.
• These chlorine atoms catalyse the decomposition of the ozone layer:
  > The free chlorines react with ozone to form chlorine monoxide (also very reactive) and oxygen.
  > The chlorine monoxide reacts with more ozone to produce oxygen and reform the free chlorine, (therefore they can continue the chain reaction).
  > Overall: two ozone molecules become 3 oxygen molecules.
• Nitrogen monoxide also catalyses this reaction.