Reactions With Alkanes

Organic Reactions

*** ALKANES ***

General Formula: CnH2n+2



Low Reactivity:


  • Saturated hydrocarbon
  • All C-C (Single Bonds)


Complete Combustion

Alkane + Oxygen → CO2 + H2O


Conditions:

Little bit of heat to get it going and plenty of oxygen


Examples:

2C4H10 + 13O2 → 8CO2 + 10H2O

Incomplete Combustion

Alkane + Oxygen → CO + H2O or Alkane + Oxygen → C + H2O


Conditions:

Little bit of heat to get it going, and not enough O2.

** Oxygen is the limiting reactant!


Examples:

2C4H10 + 9O2 → 8CO + 10H2O

or

2C4H10 + 5O2 → 8C + 10H2O


Uses/Other:

CO harmful to humans, unburned hydrocarbons produce smog

HALOGENATION

Alkane + Halogen (F2, Cl2, Br2, I2) Halogenoalkane



Conditions:

UV Light, hv


Examples:


CH4 + Cl2 → CH3Cl → CH2Cl2 → CHCl3 → CCl4

(hv) (hv) (hv) (hv)


aka


Methane + Cl2 → chloromethane →dichloromethane → chloroform (trichloromethane) → tetrachloromethane (carbontetrachloride)



Homolytic Fission:

Each electron from covalent bond goes to each atom forming free radical (unpaired electrons - very reactive)

Initiation:

The halogen molecule is broken in two identical free radical (atom with unpaired electron). The process is called homolytic fission.


Propagation:

Free radicals can react further with another alkane. No change in the number of free radicals.


Termination:

Two free radicals collide and form a covalent bond. This step decreases the number of free radicals.

Free Radical Reactions