Writing Mechanisms

Understanding the mechanisms by which organic reactions occur is one of two keys to organizing reaction information (the other is functional group identification). Simply trying to memorize all of the reactions is the road to disaster; with 35 million organic compounds out there, each reaction will look new and different unless you recognize the underlying categories into which functional groups and mechanism types place the reactions. As you study the reaction mechanisms presented in class and in the text, you should do so with pencil or pen in hand, and actually write out the steps for a specific set of reactants and products.

You must try very hard not to regard reaction mechanisms as a kind of magic, with no rational foundation, and attempt simply to memorize all of the steps. This is a dreadful mistake.

Reaction mechanisms are the most logical and easy-to-understand part of organic chemistry, if one only takes the time to think about what is happening in each step.

The overall reaction should match, both in outcome and in the roles played by the various species, one of the following ten types:

  1. Radical Substitution

  2. Radical Addition

  3. SN2

  4. SN1 - E1

  5. E2

  6. Electrophilic Addition

  7. Electrophilic Substitution

  8. Pericyclic (cyclic transition states; the Diels-Alder reaction)

  9. Nucleophilic Addition

  10. Nucleophilic Acyl Substitution

(Click on the red button to display the generic mechanism for that kind of process.)