How do you use NMR to tell the conformation of a molecule?
 

I'm looking at an NMR and its chemical shifts and J-coupling values and I need some help on using J-coupling to tell conformation. Anyone have some tips, pointers, anything?nemeczek, thankyou for your answer. I am aware of the karplus equation and finding the dihedral angle. I'm not entirely sure what to do with that information though. Can you give me a few pointers?Ensur, thankyou for trying to help. I know what my compound is supposed to be and I know the basics of reading NMR. I'm working on 1H NMR by the way. I need to know how the dihedral angle tells you the specific conformation though.

How do you use NMR to tell the conformation of a molecule?
 

Find the Karplus curve which describes the dependence of J on the value of the H-C-C-H dihedral angle.First of all, you need to be sure that the rate of interconvertion between the conformations is slow at the NMR time scale. If it is too fast, you will observe the average conformation by NMR. It can still provide you some information as to the population distribution between the conformations, though.If your molecule contains a six- or five-membered ring, the dihedral angle between H(axial)-C-C-H(axial) is obviously different than for its equatorial-equatorial counterpart. It would manifest itself in a different value of J.

How do you use NMR to tell the conformation of a molecule?
 

Which NMR are you looking at? C13 or H1?I'm most familiar with H1. What I do is just read each signal at a time. First, if I'm given the compund, I'll calculate the index of hydrogen deficiency to tell me if I have any crazy double or triple bonds or aromatic compounds.Then I'll count how many unique signals I have. And then I'll take it one at a time. If one of the signals is a 3H doublet, I can draw a C with 3 H's on it, and a second C connected to that C, with 1 H on it since the reading is a doublet (remember coupling).I wish I could help you out with 13C but, don't quite remember it as well.As for chemical shifts, http://wwwchem.csustan.edu/Tutorials/NMRTABLE.HTM will tell you what kind of substrates produce which chemical shifts. Best thing to do is just memorize them.<br />
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