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Topic: NMR  (Read 3971 times)

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Offline SME

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NMR
« on: November 02, 2010, 06:00:26 PM »
Im having trouble with a calculation...

A particular proton undergoes resonance at 75 Hz downfield from TMS for a field strength of (2.3488T) and a frequency of 100 MHz.

What would be the observed shift, in Hz, if the experiment was carried out at a frequency of 300 MHz?
What is the value of the chemical shift, delta, for this proton?
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Offline MissPhosgene

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Re: NMR
« Reply #1 on: November 02, 2010, 09:28:11 PM »
Hz =  chemical shift ( delta, ppm) * field strength (T).
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Offline SME

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Re: NMR
« Reply #2 on: November 03, 2010, 05:57:13 PM »
I'm sorry, but I still don't get it...

for the first question, how do you know what the chemical shift is? Is this not determined in the second question?

And to determine the chemical shift, do you use: Chemical shift = [(v sample - v reference)/v reference] x 106 ?

I'm confused about what the different values represent
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Offline MissPhosgene

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Re: NMR
« Reply #3 on: November 04, 2010, 09:47:57 PM »
Not quite, but really really close. Sorry for not being clear. Look at the link for clarification.

http://en.wikipedia.org/wiki/Chemical_shift#Chemical_shift_referencing
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Offline SME

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Re: NMR
« Reply #4 on: November 14, 2010, 08:11:21 AM »
I've went away and tried reading what I can... but I'm still not clear:

However:

field strength is proportional to distance, so:

Observed shift (Hz) = 3 x 75 = 225 Hz    . is this correct?

Chemical shift (ppm) = { (v sample - v reference)/v reference } x 106
                            =  225/300
                            = 0.75 ppm                                     ...is this correct
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