Chemical Shift - Chemical Shift Referencing

Chemical Shift Referencing

Chemical shift δ is usually expressed in parts per million (ppm) by frequency, because it is calculated from:

Since the numerator is usually in hertz, and the denominator in megahertz, delta is expressed in ppm.

The detected frequencies (in Hz) for 1H, 13C, and 29Si nuclei are usually referenced against TMS (tetramethylsilane) or DSS, which is assigned the chemical shift of zero. Other standard materials are used for setting the chemical shift for other nuclei.

Thus, an NMR signal that absorbs at 300 Hz higher than does TMS at an applied frequency of 300 MHz has a chemical shift of:

Although the frequency depends on the applied field the chemical shift is independent of it. On the other hand the resolution of NMR will increase with applied magnetic field resulting in ever increasing chemical shift changes.

Read more about this topic:  Chemical Shift

Famous quotes containing the words chemical and/or shift:

    If Thought is capable of being classed with Electricity, or Will with chemical affinity, as a mode of motion, it seems necessary to fall at once under the second law of thermodynamics as one of the energies which most easily degrades itself, and, if not carefully guarded, returns bodily to the cheaper form called Heat. Of all possible theories, this is likely to prove the most fatal to Professors of History.
    Henry Brooks Adams (1838–1918)

    What is the life of man! Is it not to shift from side to side?—from sorrow to sorrow?—to button up one cause of vexation!—and unbutton another!
    Laurence Sterne (1713–1768)