Rationalizing spectral data

NMR – General

As we discussed in class, always use the very best data tables you can find to predict chemical shifts and coupling constant, but remember that spectral data + assignments for a structurally analogous compound are even better than data tables. Some places you can look for spectral data on specific compounds:

• The same paper. Chemists tend to make a series of analogous molecules, replacing a methyl with a phenyl here, or a proton with a methoxy group there. If one of these molecules possesses an easily interpreted spectrum, you might be able to apply this same interpretation to your molecule’s spectra.
• Books. The Reed library contains several compilations of NMR (1H and 13C) and IR spectra (and more). Two favorites of mine are the various Aldrich Libraries (also available online) and “Tables of Spectra Data for Structure Determination of Organic Compounds,” by Pretsch et al. (QC462.85 .T313 1983).
• Online Tables. The Sigma-Aldrich site lets you look at high quality spectra for many of the compounds they sell. You get the spectra, but no interpretation. Another excellent site that actually provides assignments is maintained by Prof. Hans Reich, U. Wisconsin-Madison. I have listed links to four of his data tables, but his site contains much, much more:
  • ¹H chemical shifts
  • HH coupling constants
  • ¹³C chemical shifts
  • CH coupling constants

I have also added some other useful links for organic chemists to the site’s side bar. Check them out before the Qual.

HW #7 and the Missing Lecture

The first problem on the homework assignment asks you to predict reaction products, but because I cut my lecture off before the final page of notes, I failed to give you some crucial information.

The final page of notes can be downloaded here. Please read it before you try to work the problem.