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Sunday 7 June 2015

Stereochemistry Information from NOESY/ROESY data

NOESY_Part1Spec_Sept142009.

 
Several NMR experiments offer tools to help determine the stereochemistry of a structure. Some typical experiments are 1D NOE (Nuclear Overhauser Effect), 2D NOESY (NOE Spectroscopy) and ROESY (Rotating-frame Overhauser Effect Spectroscopy). These experiments will produce signals for nuclei that are close to each other through space independent of the number of bonds separating the nuclei.
A simplified 1H-1H NOESY spectrum is shown below. The spectrum shows 2 correlations at (4.29,1.28) and (4.29,3.13) ppm. There is no correlation to the proton signal at 2.68 ppm.

 NOESY_Part1Str_Sept142009


NOESY, ROESY, COSY and TOCSY are all 2D NMR experiments that sound so similar but offer different pieces of information about the puzzle. When interpreting the NMR data, it is important to understand how the nuclei interact with each other. For example, the presence of a cross peak (a correlation off the diagonal) on a COSY dataset is a result of nuclei coupling through a bond(s) whereas a NOESY dataset measures NOE’s (Nuclear Overhauser Effect) through space regardless of the number of bonds separating the nuclei. An NOE is typically observed for nuclei that are separated no farther than 5 Å apart.
For the enantiomers example shown below, the NOESY and COSY experiments differ in the presence or absence of the cross peaks. A clear difference between the two experiments is the information provided on the diastereotopic protons of the CH2 group.
NOESY_Part1Str_Sept142009



The NOESY spectrum, also outlined , shows 2 correlations at (4.29,1.28) and (4.29,3.13) ppm. There are no NOE's to the proton signal at 2.68 ppm. The DQF-COSY below shows two-bond and three-bond correlations at (4.29,3.13), (4.29,1.28) and (3.13,2.68) ppm. There are no four-bond correlations present as the 4J coupling constants are close to zero.



 NOESY_Part1Spec_Sept142009 NOESY_Part2DQFCOSY_Sept142009



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Alaska - Wikipedia, the free encyclopedia

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The name "Alaska" (Аляска) had been introduced in the Russian colonial period, when it was used to refer to the peninsula. It was derived from an Aleut, ...

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The City and Borough of Juneau (/ˈdʒuːnoʊ/; Tlingit: Dzánti K'ihéeni [ˈtsántʰì kʼìˈhíːnì]) is the capital city of Alaska. It is a unified municipality located on ... Map of alaska




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