The possible bonding arrangements between carbon and oxygen in organic chemistry translate to a series of oxidation states of carbon. Because oxygen (3.5 on the Pauling scale) is more electronegative than carbon (2.5), electrons shared between the two atoms are said, in oxidation-reduction, to 'belong' to oxygen. The oxidation reduction progression that proceeding from alcohol to aldehyde/ketone to carboxylic acid to carbon dioxide involves a continuous loss of 'electron control' by carbon. At one end of the scale, carbon is bonded to other carbons or hydrogen and singly bound; at the other end, carbon is doubly bound twice to oxygen. A primary alcohol beginning with an oxidation number of -1 (gaining two electrons from bonding with two hydrogens and losing one electron in bonding to oxygen), will have an oxidation state of +1 upon oxidation to an aldehyde and +3 upon further oxidation to carboxylic acid. The oxidation state of carbon in carbon dioxide is +4.

Fluent understanding of the differences between the various oxidation states of carbon in organic compounds is about as clear-cut as one can get in terms of core MCAT preparation.

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