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Wednesday, January 18, 2017

Organic Chemistry, "Function", Part 11 - Properties of Amines

Greetings,

Yet another important class of compounds is that of the Amines.  One obtains an amine compound by the substitution of a hydrocarbon hydrogen atom with an amine functional group.  The primary amine functional group is, simply, a single nitrogen atom bonded to two hydrogen atoms.  This leaves a single electron on the nitrogen atom available to bond with a carbon atom of a hydrocarbon compound.  From a much earlier post of this blog, it was shown that the nitrogen atom will tend to have a lone pair (non-bonding) of electrons.  The amine group is electrically neutral, however, nitrogen's lone pair of electrons can readily accept a hydrogen ion (proton) from solution.  This puts a positive charge on the group.

The interactions between amine molecules consist of hydrogen bonding, dipole-dipole, and London Dispersion Forces.  The combined effect of all three forces results in a dramatic increase in boiling point as molecular weight is increased.  See the chart below for a summary of molecular structure, nomenclature and boiling points for the lowest molecular weight amines.


If one imagines the "base" amine as a nitrogen atom bonded to three hydrogen atoms (and with a lone pair of electrons), then a primary amine is formed by replacing one of the hydrogen atoms with a hydrocarbon group.  A secondary amine has two hydrogens replaced and a ternary amine has all three replaced.

That's all for now.  As always, thank you for reading!

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