Chemoselectivity
CH 4 is the lowest oxidation state of carbon (most reduced); CO 2 is the highest (most oxidized).
Carboxylic acids and carboxylic acid derivatives are the most oxidized functional groups;
followed by aldehydes, ketones, and imines; followed by alcohols, alkyl halides, and amines.
Oxidation is an increase in oxidation state and is assisted by oxidizing agents.
Oxidizing agents accept electrons and are reduced in the process. They have a high affinity for
electrons or an unusually high oxidation state. They often contain a metal and a large number
of oxygens.
Primary alcohols can be oxidized to aldehydes by pyridinium chlorochromate (PCC) or to
carboxylic acids by stronger oxidizing agents, like chromium trioxide (CrO 3 ) or sodium or
potassium dichromate (Na 2 Cr 2 O 7 or K 2 Cr 2 O 7 ).
Secondary alcohols can be oxidized to ketones by most oxidizing agents.
Aldehydes can be oxidized to carboxylic acids by most oxidizing agents.
Reduction is a decrease in oxidation state and is assisted by reducing agents.
Reducing agents donate electrons and are oxidized in the process. They have low
electronegativity and ionization energy. They often contain a metal and a large number of
hydrides.
Aldehydes, ketones, and carboxylic acids can be reduced to alcohols by lithium aluminum
hydride (LiAlH 4 ).
Amides can be reduced to amines by LiAlH 4.
Esters can be reduced to a pair of alcohols by LiAlH 4.
Both nucleophile–electrophile and oxidation–reduction reactions tend to act at the highest-
priority (most oxidized) functional group.
One can make use of steric hindrance properties to selectively target functional groups that
might not primarily react, or to protect functional groups.
Diols are often used as protecting groups for aldehyde or ketone carbonyls.
Alcohols may be protected by conversion to tert-butyl ethers.
