Organic chemistry/Mechanisms

Terminology
Mechanisms are a set of figures that uses arrows to indicate electron flows inside a molecule or between molecules. The arrow starts from the nucleophile and points towards the electrophile. In acid-base reactions, for instance, they start from the base and point towards acidic hydrogen or Lewis acid.

Examples
Unimolecular Elimination (E1) Mechanism: X*               H        |                 |  (+)       base H3C — C — CH3 ---> H — C — C — CH3 --> H — C == C — CH3 + H2O |                |   |                        |    |        CH3               H   CH3                      H    H

Bimolecular Elimination (E2) Mechanism: X  H      |   |       strong base H — C — C — H -> H — C == C — H      |   |                         |    | H  H                         H    H

Unimolecular Substitution (SN1) Mechanism: Ex: Solvolysis                                   H                                                   | X                      H              H — O(+)H                    OH        |                  (+)  |      H2O         |   |                    | H3C — C — CH3 ---> H3C — C — C — H -> H3C — C — C — H  --> H3C — C — CH3 |                  |   |                  |   |       -(H+)        | CH3                CH3 H                  CH3 H                    CH3

Note: SN1 reactions produce racemates due to the achiral carbocation intermediate.

Bimolecular Substitution (SN2) Mechanism: X                                                 H     |        good nucleophile (I, BR, Cl, OH...)       | H — C — CH3 -> H — C — CH3 |                                                 |     H                                                  I Note: SN2 reactions undergo inversion of configuration.


 * represents any good leaving group (i.e: Cl, Br, I, TsO, etc...)