Question

Using a 300 MHz NMR instrument:

a. How many Hz downfield from TMS is a signal at 2.5 ppm?
b. If a signal comes at 1200 Hz downfield from TMS, at what ppm does it occur?
c. If two peaks are separated by 2 ppm, how many I-AZ does this correspond to?

Answer 1

a. 750Hz, b. 4.0ppm, c. 600Hz

Step-by-step explanation:

The Downfield Shift (Hz) is given by the formula

Downfield Shift (Hz) = Chemical Shift (ppm) x Spectrometer Frequency (Hz)

Using the above formula we can solve all three parts easily

a. fspec = 300 MHz, Chem. Shift = 2.5ppm, 1MHz = 10⁶ Hz, 1ppm (parts per million) = 10⁻⁶

Downfield Shift (Hz) = 2.5ppm x 300MHz x (1Hz/10⁶MHz) x (10⁻⁶/1ppm)

Downfield Shift = 750 Hz

The signal is at 750Hz Downfield from TMS

b. Downfield Shift = 1200 Hz, Chemical Shift = ?

Chemical Shift = Downfield shift/Spectrometer Frequency

Chemical Shift = (1200Hz/300MHz) x (1ppm/10⁻⁶) = 4.0 ppm

The signal comes at 4.0 ppm

c. Separation of 2ppm, Downfield Shift = ?

Downfield Shift (Hz) = 2(ppm) x 300 (MHz) x (1Hz/10⁶MHz) x (10⁻⁶/1ppm) = 600 Hz

The two peaks are separated by 600Hz