Integrated SequencePhysics Chemistry Organic Biology

Web Resources

  click if a link is broken

Special points of emphasis

Work, Energy, and Power


The Chemical Bond


Chemical Thermodynamics and the Equilibrium State

Reactions of Aldehydes and Ketones

An aldehyde or ketone in aqueous solution exists in an equilibrium with its hydrate (the adduct of the aldehyde or ketone with water). The position of equilibrium depends on the degree of substitution of the aldehyde or ketone. The more highly substituted the aldehyde or ketone, the less hydrate is present at equilibrium. The determination of comparative equilibrium position rests on two influences, both of which operate so that more highly substituted aldehydes and ketones are less likely to form hydrates.

First, the aliphatic groups donate electrons by induction. The shift of negative electron density toward the positive pole of the carbonyl carbon represents on the molecular level a decrease in electrostatic potential energy for highly substituted aldehydes and ketones, an internal energy decrease. A more substituted aldehyde or ketone possesses less free energy compared to its hydrate, moving equilibrium away from hydration.

The second reason that greater substitution makes the hydrate less favorable is that as an aldehyde or ketone interconverts with its hydrate, its geometry shifts from trigonal planar to tetrahedral, and in the new geometry, steric hindrance is more of a factor in determining the internal energy of the substance. In other words, the more highly substituted the aldehyde or ketone, the higher the internal energy of the hydrate product because of steric hindrance. This factor acts to increase the relative free energy of the product of hydration for highly substituted aldehydes and ketones. In summary, with greater substitution, induction by the carbonyl group works to decrease the free energy of the aldehyde/ketone and steric hindrance works to increase the free energy of the hydrate, both of which push the equilibrium away from the hydrate for highly substituted aldehydes and ketones.

Chemical Kinetics

Organic Acids and Bases

Reactions of Aldehydes and Ketones

Hydration may be either acid or base catalyzed. With base catalysis, the hydroxyl group carries out a faster nucleophilic addition step than normal water. System pH is maintained as the base regenerates when the tetrahedral intermediate abstracts a proton from water in the final step of hydration. Acid catalysis, on the other hand, begins with protonation of the carbonyl oxygen, activating the carbonyl group for nucleophilic attack by water.

The WikiPremed MCAT Course is a free comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum.

Please read our policies on privacy and shipping & returns.  Contact Us.
MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course.

Creative Commons License
The work of WikiPremed is published under a Creative Commons Attribution Share Alike 3.0 License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions. You can use the resources here for commercial or non-commercial purposes, but please give attribution and a link to the production credits and edit history of the resource. For the works here which began as my individual work, please attribute "John Wetzel, an author at".