Hydrogen bonding plays a significant role in determining the physical properties of amines, although the hydrogen bonds in amines are not as strong as the hydrogen bonding that occurs in alcohols. Amines are intermediate in boiling point between similar alkanes and alcohols. Amines with fewer than six or seven carbons are water soluble.

The acid-base properties of amines are very important. Of neutral organic molecules, amines are the strongest bases, although amines are still technically weak bases with basicity constant, Kb, between 10-3 to 10-5.

Here is an interesting discussion of the comparison of the basicity of different types of amines: Ammonia is more basic than primary amines which are themselves more basic than tertiary amines which are in turn more basic than secondary amines. Notice the irregularity of this pattern. This strange order of basicity occurs because of the combination of two effects, the stabilization of alkylammonium cation by the inductive release of negative charge by the alkyl substituents. The other effect, which tends in the opposite direction, is the ability of water to solvate and stabilize the cation through hydrogen bonding. While tertiary ammonium cations are more stabilized by induction, secondary ammonium cations are more stabilized by solvation.

How would the MCAT handle this type of material? This kind of discussion typifies content within a certain species of MCAT passage where the test-writer is not concerned that you had seen and retained this advanced material from your coursework but whether you have the overall fluency and comfort level to read the discussion with comprehension.

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