Organic Chemistry Reactions

Question 1

Type of reactions alkanes undergo and state the conditions.

Answer 1

Alkanes undergo combustion and substitution reactions.

Can undergo combustion as burns readily in excess oxygen.

Can undergo substitution by Cl or Br in presence of UV light or very strong heating.
Observation: White fumes of HBr and HCl produced.
Mixture of products produced so not a good preparatory technique.

Question 2

Why can halogenoalkanes undergo substitution?

Answer 2

C-X bond is polar since halogen atom has higher electronegativity than C atom. Reactive C atom is electron deficient. Thus, halogenoalkanes undergo substitution reactions where halogen atom is replaced by species attracted to electro deficient C atom.

Question 2

Type of reactions alkanes undergo and state conditions.

Answer 2

Combustion, Addition of halogen and Addition of hydrogen (reduction).

Addition of halogen: Cl2/ Br2 in CCl4 or Br2(l). Dark, room temperature.
Observation: Orange-red Br2 in CCl4/ Reddish brown Br2 turns COLOURLESS.

Addition of hydrogen: H2(g). Ni catalyst, heat, room temperature

Question 2

Conditions for Halogenoalkanes to undergo substitution and elimination.

Answer 2

Aqueous KOH, heat with reflux results in substitution

Ethanolic KOH, heat with reflux results in elimination

Question 3

Reagents for alcohols to be eliminated.

Answer 3

Excess concentrated H2SO4, heat

Question 4

Reagents for alcohols to be oxidised into carboxylic acids

Answer 4

K2Cr2O7 for all types of alcohols can be used. H2SO4, heat with immediate distillation for primary alcohol, heat under reflux for secondary alcohol. Tertiary not oxidised by any oxidising agent.

Question 5

Reagents for alcohols to undergo esterification or condensation.

Answer 5

RCOOH, trace amount of concentrated H2SO4, heat under reflux.