NMR Theory

James Keeler: Understanding NMR Spectroscopy
The Basics of NMR
Principles and Application
Problems in NMR Spectroscopy

Probes at Varian
Brief descriptions of different experiments
Whole bunch of experiments on codeine

COSY-45 vs COSY-90
The diagonal is cleaner.
All geminal, many vicinal and some long range couplings appear.
Geminal couplings can be identified from HSQC, and eliminated from consideration.
Long range couplings have low intensity and tend to appear on the F2 side of the diagonal.
Vicinal and geminal couplings tend to slant different directions. EurJOC, (2008), 2671-2688.

DQF-COSY is really for determining H,H coupling constants, but this information can be obtained more easily form 1D-TOCSY.
Requires a decent amount of sample (less sensitive than COSY by a factor of 2) and quite a lot of time. You need a lot of time because you need a lot of increments to get enough resolution in T1 to avoid the cancellation of adjacent signals. There are published procedures on how to narrow the spectral window and computationally remove the aliased signals. In principle, that would let you “zoom in” on a particular multiplet to get its couplings, but it’s complicateed in practice. However, one case where it might come in handy is where the spectrum has a lot of singlets in it arising from methyl groups. They don’t show up in DQF-COSY, so they won’t swamp the spectrum.http://www.thechemblog.com/?p=1037