Inside the NMR Spectrometer

Normal nuclei Nuclei in a magnetic field Radio waves will ‘pulse’ these nuclei to stimulate a response that can be recorded

The nuclei’s response to the ‘pulse’ is then recorded as a peak (or set of peaks) which will be placed on a graph (see above). These peaks are always reference to TMS (tetramethylsilane = 0 ppm) Where the peaks occur depends on the shielding or deshielding effects experience by that nuclei.

Approximate ppm of certain H’s (Note: Additional deshielding can change these values)

Very Shielded Very deshielded Note: Remember these values will change if there is additional deshielding effects.

N + 1 Rule N = N + 1 = 1 peak N + 1 = 2 N + 1 = 3 N + 1 = 4 N + 1 = 5

Example #1

Example #2 – Integration 2 cm 6 cm 2/2 = 1 equiv H’s 1 x 3 = 3 H’s 6/2 = 3 equiv H’s 3 x 3 = 9 H’s -Divide by 2, because it is the lowest out of all the distances -You may need to multiply by some whole number until you reach the appropriate amounts of H’s (Fudge Factor).

We can also use 13C NMR *Approximate range (ppm) of different carbons

Time = 5 minutes of scanning Time = 1 hour of scanning (or more)

Be sure to follow this example in the workshop! Pieces of the Puzzle # of Unsaturations = #C - #H/2 - #Hal/2 + #N/2 +1 C = Carbon H = Hydrogen Hal = Halogens N = Nitrogen Be sure to follow this example in the workshop!

J Value Examples