Question

A 1H NMR signal is observed at 195.0Hz (downfield of TMS) on a 1.20x10^2-MH2 instrument. What is the observed chemical shift in parts per million (ppm)?

Answer 1

The observed chemical shift of the 1H NMR signal on a 1.20x10^2-MHz NMR instrument is calculated to be 1.625 ppm.

Step-by-step explanation:

The student has asked about the calculation of the observed chemical shift in parts per million (ppm) for a 1H NMR signal using a 1.20x102-MHz NMR instrument. To calculate the chemical shift in ppm, you divide the frequency of the NMR signal by the frequency of the NMR instrument and then multiply by 106 (to convert to ppm).

Here's the step-by-step calculation:

1. Divide the observed frequency (195.0 Hz) by the instrument frequency (1.20x102 MHz which is 1.20x105 Hz).
2. Multiply the result by 106 to convert to ppm.

Chemical shift (δ) = (195.0 Hz / 1.20x105 Hz) x 106 ppm

When you calculate δ, you get:

δ = (195.0 / 1.20x105) x 106 ppm

= 1.625 ppm (rounded to three decimal places)

Therefore, the observed chemical shift is 1.625 ppm.