Integrated SequencePhysics Chemistry Organic Biology

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Special points of emphasis

Periodic Properties

The Chemical Bond

Reactions of Aldehydes and Ketones


Oxidation-Reduction in Organic Chemistry

Carbon is in a progressively more oxidized state from alkanes to alcohol to aldehyde/ketone to carboxylic acid to carbon dioxide. Progressing up the scale involves a continuous transfer of 'electron control' from carbon to oxygen. Because oxygen (3.5 on the Pauling scale) is more electronegative than carbon (2.5), in terms of oxidation-reduction, electrons shared between the two atoms within covalent bonds are said to belong to oxygen. At the aliphatic end of the scale, carbon is bonded to other carbons or hydrogen; at the oxidized end, carbon is bound to oxygen. A carbon in a primary alcohol is in a relatively reduced state, with an oxidation number of -1 (gaining two electrons from bonding with two hydrogens and losing one electron in bonding to oxygen). This carbon will have an oxidation state of +1 upon oxidation to an aldehyde and +3 upon further oxidation to carboxylic acid.

Reactions of Aldehydes and Ketones



Bioenergetics and Cellular Respiration

Integration of Metabolism

The oxidation-reduction progression involving alcohols, aldehydes/ketones, carboxyl groups, and carbon dioxide is important both for biosynthesis and energy metabolism. Here are a few more examples which are good to contemplate for the MCAT. Contemplation is not the same thing as memorizing dozens of biochemical pathways before the exam.

The conversion of pyruvate to lactate involves reduction of a carbonyl group to a hydroxyl group.

The carbonyl group in an acetoacetyl group is reduced, on its way to forming a purely aliphatic chain, in fatty acid synthesis.

The corticosteroids cortisol and cortisone differ from each other by the reduction of a single carbonyl group.

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