19.10 : アミンのNMR分光法

The proton NMR spectrum of an amine shows the N–H signal as a broad band in the region of 0.5 to 4 ppm.

The peak's position depends on the extent of hydrogen bonding, the solvent's nature, the amine's concentration, and the temperature conditions.

Because the N–H protons are easily exchangeable, no coupling occurs with the neighboring protons—the peak is broad, unsplit, and difficult to identify.

A D₂O shake exchanges the N–H protons for the N–D deuterons causing the N–H peak to disappear, confirming the presence of amine protons in the sample.

Since the α carbon protons are deshielded by nitrogen, they have higher chemical shift values than the β carbon protons that are far less deshielded and appear further upfield.

In the ¹³C NMR spectrum, the α carbon shows the highest chemical shift as the nitrogen atom greatly deshields it.

An increasing distance between carbon and nitrogen decreases the deshielding effect, causing the carbon atom's chemical shift value to decrease.