[organicadam94]

(Sorry for the repeat posting, I accidentally used the wrong section and couldn't work out how to move the old post)

Hi All,

I've been looking at ways to "quantify" the amount of residual solvent/starting material etc in my crude NMR's to get a rough idea of how much product I'm likely to recover after purification.

Obviously (at least I hope so, or my understanding of NMR is fundamentally flawed), it's fairly easy to do in terms of mol/mol.  If 1H of compound is set to integrate to 1, and the CH2Cl2 peak integrates to 0.2 then you're basically just taking a ratio of the integrals:  1H product = int 1, 1H CH2Cl2 = int 0.1 then the sum is 0.1 / 1 = 0.1 mol of CH2Cl2 for every mol of compound.

What I'm a little less certain of is how to turn this into a mass ratio.     The only approach I can find on the internet, without the need for a quantified internal standard is the one found in "practical NMR for organic chemists" by Hollerton and Richards.

They take the mol ratio and multiply it by  (MWt CH2Cl2 / MWt Compound).. which they then say gives the %w/w.... this is where my understanding fails me.   Firstly, I'm just not sure how they come about this calculation (when I sit down and think about how to do it using n = mass / Mr etc, I can't derive their calculation) and secondly, because my understanding of %w/w comes from solution chemistry, where a 10% w/w solution of NaOH for example, would be 10 g of NaOH in 90 g of H20, and NOT 10 g NaOH in 100 g H2O, which is what I think the calculation from Hollerton and Richards would give me, since it doens't take into account any of the other crap which may be in my sample

Would anyone be able to explain to me how this %w/w works from the calculation above, or provide me with their way of working out the relative weight of solvent etc in their NMR samples.

Thanks in advance
A