NMR Lecture Part 2

NMR Lecture Part 2 - 2D NMR Two dimensional NMR has two...

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2D NMR Two dimensional NMR has two arrayed time dimensions. t 2 is the ordinary FID acquisition time that we saw in 1D NMR. t 1 is given a different value for each collected FID to create a signal surface. FT is performed along each time dimension to create the 2D frequency spectrum.
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2D NMR The main advantage to 2D NMR is that more information can be included in spectra without risk of overlap However, more stringent requirements for clean spectra Pulse angle precision Phase cycling Broadband decoupling Solvent suppression These are generally automatically handled by preprogrammed pulse sequences, but it’s good to remain aware of their existence
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Isotope Channels Different nuclear isotopes have very different resonance frequencies at a given field. Thus, when one type of nucleus is pulsed, other types are unaffected. Each isotope has its own hardware for producing the pulse. Can pulse using different channels simultaneously.
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Product Operators (revisited)
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COSY Correlation Spectroscopy Identifies “through bond” correlations between nuclei Helps remove possible ambiguity of 1D spectra Ex. Suppose the following spectrum contains information about two different molecules, with identical J-coupling Which peaks belong to which molecule?
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COSY Three possible interpretations of the 1D spectrum exist
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COSY COSY provides us with a “correlation map” to see which spins belong to the same system. Diagonal peaks represent the 1D spectrum Off diagonal peaks represent correlations
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COSY The pulse sequence includes two 90 pulses separated by an evolution time t 1 .
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This document was uploaded on 01/03/2012.

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NMR Lecture Part 2 - 2D NMR Two dimensional NMR has two...

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