Chordate - 13-4-2012 at 09:18
So, I thought I was pretty good working on the millimole/submillimole scale with some of my synthesis and getting okay yields, but someone was showing
me some of their natural products work and I sharing some difficulty characterizing the product of a certain step.
So I sez "carbon NMR should clear that right up though, right?" And he grinned and politely informed me that he was working with .7 milligrams of
material.
This... Blows me away. He is getting 80+ percent yields on some of these steps working with MAYBE 2 milligrams of material.
I want this skill. Are there any good references that can help me make the transition from microscale to... Nanoscale and beyond? Or is this just
something one picks up after 10 years of dedicated labwork?
GreenD - 13-4-2012 at 11:42
Ask him how much solvent he uses.
NMR also doesn't destroy the compound 
DJF90 - 14-4-2012 at 12:37
For a carbon NMR he's going to need at least 3-4mg even with very NMR facilities. The recommended quantity for a standard 5mm NMR tube with 0.75ml
solvent is 2mg for 1HNMR, 10mg for 13CNMR, on a 400MHz machine. He might be lucky to get a reasonable resolution if he has access to a 900MHz, or even
maybe a 700MHz machine.
Regarding microscale work, I frequently partake on reactions using somewhere between 100mg and 1g of material. In some instances, I even work down to
10-25mg, but I try to avoid it if I can; this is often impossible when I'm working with a small stock of material (300mg-ish atm) that has taken 7-8
steps to make and need to do lots of different screening reactions with. Recovering material from such failed reactions is a pain, but its far better
than when the material gets chewed up 
I can imagine theres probably a decent
amount of error in your colleagues weighings, even with a "standard" organic lab balance (0.1mg resolution).