Chapter 09: Alkanes
Worked Example 1:
A mixture of 2-methylbutane and bromine is allowed to react in the presence of sunlight. How many products are formed and what is the ratio in which they are formed?
a) 2 products; 1:3
b) 3 products; 3:6:2
c) 4 products; 6:1:2:3
d) 5 products; 4:3:1:2:2
Answer: c) 4 products; 6:1:2:3
More questions to take note:
1) Why do alkanes not react with I₂?
- Weak C-I and H-I bonds formed causes the 1st propagation step to be endothermic, preventing the formation of iodoalkanes.
2) Why do alkanes not react with aqueous Cl₂?
- The presence of polar water molecules in aqueous Cl₂ will polarise Cl₂ to break.
heterolytically, causing a disproportionation reaction where HOCl and HCl are formed instead of the desired chloroalkane.
Stability of Radicals
More alkyl groups attached to the carbon radical will result in an increase in stability of the carbon radical:
Alkyl groups are generally electron-donating, thus more alkyl groups attached to the carbon radical causes it to be less electron deficient and the radical is more stable.