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?

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

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

b. accuracy of the data matters alot more than its number of digits, organization or amount of detail. quantitative observation is more accepted than the qualitative observation.

the answer is d. 74.02