Oxidation–Reduction Reactions
More positive compounds are more electrophilic.
Alcohols, aldehydes, ketones, carboxylic acids, and their derivatives can act as electrophiles.
Leaving groups are the molecular fragments that retain the electrons after heterolysis.
The best leaving groups can stabilize additional charge through resonance or induction.
Weak bases (the conjugate bases of strong acids) make good leaving groups.
Alkanes and hydrogen ions are almost never leaving groups because they form reactive anions.
Unimolecular nucleophilic substitution (SN 1 ) reactions proceed in two steps.
In the first step, the leaving group leaves, forming a carbocation, an ion with a positively
charged carbon atom.
In the second step, the nucleophile attacks the planar carbocation from either side, leading to
a racemic mixture of products.
SN1 reactions prefer more substituted carbons because the alkyl groups can donate electron
density and stabilize the positive charge of the carbocation.
The rate of an SN1 reaction is dependent only on the concentration of the substrate: rate =
k[R–L]
Bimolecular nucleophilic substitution (SN 2 ) reactions proceed in one concerted step.
The nucleophile attacks at the same time as the leaving group leaves.
The nucleophile must perform a backside attack, which leads to an inversion of
stereochemistry.
The absolute configuration is changed—(R) to (S) and vice-versa—if the incoming nucleophile
and the leaving group have the same priority in the molecule.
SN2 reactions prefer less-substituted carbons because the alkyl groups create steric hindrance
and inhibit the nucleophile from accessing the electrophilic substrate carbon.
The rate of an SN2 reaction is dependent on the concentrations of both the substrate and the
nucleophile: rate = k[Nu:][R–L]
The oxidation state of an atom is the charge it would have if all its bonds were completely ionic.
