Overview

¹H nuclear magnetic resonance spectroscopy tells us about the environment of the hydrogen atoms in a molecule. The technique is based on exactly the same principles as ¹³C NMR spectroscopy: the ¹H nucleus has nuclear spin 1/2, so when placed in a strong magnetic field it can exist in higher or lower energy states. When the nucleus is irradiated, it absorbs radiofrequency radiation, and nucleii in lower energy spin states are promoted to higher energy spin states.

There are important differences between ¹H and ¹³C NMR spectroscopy. The main one is that the ¹H atom, which has nuclear spin, comprises 99.98% of naturally occurring hydrogen. Consequently, most ¹H NMR spectra can be measured by a single scan, and Fourier transform methods are used only in exceptional circumstances. This means that peak areas are proportional to the number of hydrogen atoms that the peak represents, and this is very valuable when analysing spectra.

Another important difference is that since ¹²C, the main carbon isotope, does not possess nuclear spin, most hydrogen atom spectra do not have any splitting from the carbon atom to which the hydrogen is attached. The few hydrogen atoms which are attached to ¹³C atoms and hence are split produce tiny peaks which are usually lost in the background electronic noise on the spectrum. Consequently, we need consider only ¹H to ¹H coupling, unless we have present other atoms with nuclear spin such as fluorine or...