Organic Chemistry (Types of Reactions)

Question 1

Name the reactions involving alkanes.

What are the conditions?

Answer 1

1. Combustion. (excess oxygen)
   Reaction is highly exothermic
2. Free-radical substitution by halogens (chlorine/bromine)

Condition: strong sunlight or UV light to form halogenoalkanes

Question 2

Name the reactions involving alkenes.

What are the conditions?

Answer 2

1. Combustion (excess oxygen)
   Reaction is highly exothermic
2. Addition of Hydrogen (Reduction) - hydrogenation

Condition: H(2) gas with nickel catalyst, at high temperature and high pressure

OR

H(2) with platinum catalyst at room temperature

3. Electrophilic addition by Bromine and Steam
   (i) Conditions for electrophilic addition by Bromine

Cl(2) in CCl(4) or Br(2) in CCl(4)
at room temperature in the absence of light/in the dark

E.g. Observation when ethene is bubbled into Br(2) dissolved in CCl(4) in room temperature in the dark.
Observation: The reddish-brown colour of Br(2) in CCl(4) in rapidly decolourised.

Explanation: Br(2) is added across the C=C bond to give 1,2-dibromoethane via electrophilic addition mechanism.

(ii) Conditions for electrophilic addition by steam
Lab: Cold concentrated H(2)SO(4), followed by boiling with water

OR

Industrial method:
Steam and H(3)PO(4) - catalyst, high temperature and high pressure (60atm)

Question 3

Name the reactions involving alcohols.
What are the conditions?
What are the observations for each reagent?

Answer 3

1. Combustion (excess oxygen)
2. Oxidation to carboxylic acids
   ‘Oxidation’ = require oxidising agent

Reagent 1: K(2)Cr(2)O(7) = Potassium Dichromate
Reagent 2: KMnO(4) = Potassium Manganate (VII)

Condition for both reagents: H(2)SO(4), Heat under reflux

Observation:

Reagent 1: K(2)Cr(2)O(7), the solution the solution turns from orange Cr(2)O(7) (2-) to green Cr (3+).

Reagent 2: KMnO(4) the purple solution is decolourised MnO(4) (-) -> Mn (2+)

Products: carboxylic acid + water

Question 4

Name the reactions involving carboxylic acids.

Answer 4

1. Reactions with reactive metals
2. Reactions with bases
3. Reactions with carbonates
4. Reactions with alcohol to form sweet smelling esters when heated under reflux in presence of a few drops of concentrated sulfuric acid.