How to use and interpret C NMR?

[osskall]

Could someone explain to me how to use and interpret C NMR? For proton NMR there are (fairly) simple coupling rules from which to deduce that there, e.g., are two protons on a carbon next to a CH3 group. Is there anything alike for multinuclear NMR? Titanium NMR would be fun to do also, or won't I get any useful information from that? As I understand it you don't need to enrich your samples to run 11- or 13C NMR or Ti NMR. That seems convenient

 

[movies]

You generally don't see the same splitting in 13C NMR as you do in 1H NMR because the natural abundance of 13C is only about 1.5%. To see 13C-13C splitting you would need to have two adjacent 13C atoms in your molecule, which is unlikely based on the natural abundance.

Since the natural abundance is so low, you need either a lot more sample to collect a 13C spectrum, or you can observe the sample over many more scans (basically repeating the same experiment and accruing all the data). For example, a standard 1H NMR spectrum requires 8 scans to get good resolution, while a standard 13C NMR spectrum requires anywhere from 256 to 1024 scans (more if you have a very small amount of material).

Generally 13C NMR is "proton decoupled," meaning that the splitting between the carbons and the attached protons is calculated out so you just see the carbon signal. There are special NMR experiments that you can use to determine the relationship between 13C and 1H NMR peaks, but these are not necessary for most uses.

NMR of metal atoms is very useful to organometallic chemists. Many metals are NMR active. It's especially useful for simply telling whether or not your metal has been completely ligated by whatever ligand you have added because the metal NMR resonance will shift. Sometimes you can see coupling between the nuclei of the ligand and the metal, especially in metal-phosphorus complexes. I don't have any experience with Ti NMR, so I don't know if it has any NMR active isotopes that are naturally abundant, but I have a little experience with 195Pt NMR. Very interesting stuff!