Mechanisms 1

Here are the mechanisms for 3 types of reactions. Free Radical Substitution for alkanes, Electrophilic Substitution for alkenes and Nucleophilic Substitution for Halogenoalkanes/Alkyl Halides.

Alkanes mainly go through Free Radical Substitution (FRS) reactions, combustion as well as cracking. Since i have not included any mindmaps on alkanes, i shall proceed to describe more about alkanes for our syllabus. Hydrogen atoms are substituted by halogen atoms in FRS.

Combustion reactions for alkanes have a general equation of:

C_xH_y + ( x + y/4) O₂ (g)→ xCO₂ (g) + (y/2) H₂O (l)

Typical alkane questions would usually involve the application of this equation so i think it's important to memorise it. There will be clues to helping you find the values of x and y in the equation. One particular type i noticed is that they like to do combustion then run the resultant gas through limewater to remove the CO_{2. From there, just determine the number of moles of CO2} and you have found the value of x! Note that water formed is in liquid state, not gaseous state in the equation.

Another reaction to remember that alkanes undergo is cracking, which involves the breaking up of a large molecule to smaller molecules. Hydrogen gas is produced from cracking reactions.

For more information about Halogenoalkanes or Alkenes, please refer to the Chemistry section and search for a post with the appropriate title.

Mechanisms for the 3 reactions: