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lecture8_TOCSY_NOESY - Todays Lecture 10 Wed Oct 23...

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A. S. Edison University of Florida Fall, 2009 Today’s Lecture 10) Wed, Oct 23: Homonuclear 2D experiments a. TOCSY: Introduction to Isotropic mixing and effective field strength b. NOESY: Introduction to the NOE c. Phase cycling
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A. S. Edison University of Florida Fall, 2009 Before we get to TOCSY, let’s review J coupling 1 H NMR 1D spectra of Methyl α -D-Arabinofuranoside in CD 3 CN. Collected at 11.7 T by Jim Rocca in AMRIS. All of the splittings are J couplings
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A. S. Edison University of Florida Fall, 2009 J coupling Normal spectrum Decouple 4.93 ppm Decouple 4.05 ppm J coupling allows you to identify atoms within 3 (sometimes more) covalent chemical bonds. This will be even more powerful when we get to 2D NMR experiments.
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A. S. Edison University of Florida Fall, 2009 2D COSY 90x 90x t 1 t 2 As you have shown by product operators, the COSY sequence correlates resonances that are coupled together through J-coupling. Each time period ( t 1 and t 2 ) gives rise to a frequency axis in the 2D spectrum. Coupled spins can be identified by cross-peaks in the spectrum.
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A. S. Edison University of Florida Fall, 2009 ppm 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 ppm 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 2D COSY gives all the J-coupling information simultaneously Each pair of coupled spins shows up as a cross-peak in a 2D COSY spectrum. The diagonal peaks correspond to the 1D spectrum.
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A. S. Edison University of Florida Fall, 2009 TOCSY OVERVIEW TOCSY (Total Correlation Spectroscopy) is capable of correlating all spins in a coupled network (examples shown on the next slide). The “working end” of the TOCSY pulse sequence is an isotropic mixing sequence that is a sequence of pulses that are designed to remove all chemical shift differences and create a strong coupling environment. This is called the Hartmann-Hahn condition. Sometimes the TOCSY experiment is called HOHAHA (Homonuclear Hartmann- Hahn). Several mixing sequencings have been developed. The most popular are MLEV-17, WALTZ-16, GARP, and DIPSI. These all apply a series of pulses with either different phases or different lengths or both.
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