When organic molecules are bombarded with high energy electrons in a magnetic field, the molecules break into smaller fragments, which then travel through the field and separate based on charge and size. When these fragments are detected a spectrum results in which the X-axis (m/z) is based on the mass of the fragments and the Y-axis relates to the number of each fragment. Since “z” usually equals one, the X-axis is therefore simply the mass of each fragment.

Click on the image to open a Mass Spec problem set (PDF).

Magnetically active nuclei (¹H, ¹³C, ³¹P, etc.) respond to radiofrequency input when in the presence of an external magnetic field. When a sample contains these atoms in different magnetic environments it takes different frequencies of energy to promote different nuclei; we measure those energies and a spectrum results which is usually standardized using an x-axis of parts per million. Signal position, size, and shape all provide useful information on molecule structure.

Click on the image to open an H NMR tutorial (PDF).

Click here to open H NMR unknown problems (PDF).

Carbon 13 is the magnetically active form of carbon and although it is only present as less than 1% of the isotopic distribution it is measurable in NMR spectroscopy. The scale changes, with the X-axis representing signals in the 0-200 ppm region, however the same ideas of chemical shift and the number of signals still apply. Carbon NMR are often reported as the proton-decoupled variant to avoid complications from multiplet signal overlap.

Click on the image to open a C NMR tutorial (PDF).

Click here to open C NMR unknown problems (PDF).