Question

A ¹H NMR signal is observed at 101.0 Hz (downfield of TMS) on a 1.20 x 10²-MHz instrument.

What is the chemical shift, in parts per million (ppm), if the sample is analyzed with a 500.0-MHz instrument?

Answer 1

The chemical shift for the ¹H NMR signal on a 500.0-MHz instrument is the same as that on a 1.20 x 10²-MHz instrument, which is 0.8417 ppm.

Step-by-step explanation:

The student is asking how to calculate the chemical shift in parts per million (ppm) when the frequency of the ¹H NMR signal changes due to the use of a different strength NMR instrument. Chemical shift is independent of the spectrometer's frequency, and is calculated using the formula:

δ (ppm) = (observed frequency difference from TMS / spectrometer frequency) × 10⁶

For the original 120 MHz spectrometer:

• δ = (101.0 Hz / 1.20 x 10² MHz) × 10⁶
• δ = 0.8417 ppm

Since the chemical shift is independent of the spectrometer's frequency, the chemical shift on a 500.0-MHz instrument would be the same:

• δ = 0.8417 ppm