Question

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 signals are separated by 2 ppm, how many Hz does this correspond to?

Short answer

Answer

a. 750 Hz

b. 4 ppm

c. 600 Hz

Step-by-step solution

Chemical shift

The chemical shift indicates the resonant frequency of a standard compound. The $\delta$ scale is used for measuring chemical shifts.

Upfield and downfield

• An upfield signal has low energy and ppm value.
• A downfield signal has high energy and ppm value.

Identifying the chemical shift 

The chemical shift (in ppm) on the scale can be using the given formula:

chemical shift (in ppm on $\delta$scale)

$=\frac{observedchemicalshift(in{H}_Z)dowmfieldfromTMS}{vofNMRspectrometer(inM{H}_Z)}$

a. The chemical shift is 2.5 ppm.

of NMR is 300 MHz.

The observed chemical shift (in Hz) that is downfield from TMS can be found as shown:

chemical shift (in ppm on $\delta$scale) $=\frac{Observedchemicalshift(in{H}_Z)downfieldfromTMS}{vofNMRspectrometer(inM{H}_Z)}$

$2.5ppm=\frac{x{H}_Z}{300M{H}_Z}$

x=750 H_Z

b. The observed chemical shift in Hz is 1200 Hz.

of NMR is 300 MHz.

The chemical shift (in ppm) can be found as shown:

$2.5ppm=\frac{x{H}_Z}{300M{H}_Z}$

x =4 ppm

c. The chemical shift is 2 ppm.

of NMR is 300 MHz.

The observed chemical shift (in HZ) that is downfield from TMS can be found as shown:

$2.5ppm=\frac{x{H}_Z}{300M{H}_Z}$

x=600H_Z