hydrogen). Reduction refers to a decrease in oxidation state, or a gain in electrons. In organic
chemistry, it is often easier to view reduction as increasing the number of bonds to hydrogen.
OXIDIZING AGENTS AND REACTIONS
As we mentioned above, oxidation refers to an increase in oxidation state. Oxidation of a carbon
atom occurs when a bond between a carbon atom and an atom that is less electronegative than
carbon is replaced by a bond to an atom that is more electronegative than carbon. In practice, this
usually means decreasing the number of bonds to hydrogen and increasing the number of bonds to
other carbons, nitrogen, oxygen, or halides.
KEY CONCEPT
One can organize the different functional groups by “levels” of oxidation:The oxidizing agent is the element or compound in an oxidation–reduction reaction that accepts
an electron from another species. Because the oxidizing agent is gaining electrons, it is said to be
reduced. Good oxidizing agents have a high affinity for electrons (such as O 2 , O 3 , and Cl 2 ) or
unusually high oxidation states (like Mn7+ in permanganate, ; and Cr6+ in chromate,
).
Primary alcohols can be oxidized by one level to become aldehydes, or can be further oxidized to
form carboxylic acids. This reaction commonly proceeds all the way to the carboxylic acid when
using strong oxidizing agents such as chromium trioxide (CrO 3 ) or sodium or potassium dichromate
(Na 2 Cr 2 O 7 or K 2 Cr 2 O 7 ), but can be made to stop at the aldehyde level using specific reagents such as
pyridinium chlorochromate (PCC). Secondary alcohols can be oxidized to ketones.
Level 0 (no bonds to heteroatoms): alkanes
Level 1: alcohols, alkyl halides, amines
Level 2: aldehydes, ketones, imines
Level 3: carboxylic acids, anhydrides, esters, amides
Level 4 (four bonds to heteroatoms): carbon dioxide