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Logic Puzzle #11: Pairwise Correlation Confidence … Solution

Long range 2D NMR experiments do not necessarily provide information about all the connectivities. The following structure elucidation problem set is one such example.

Based on the 1H-13C HMBC shown below, there is no evident correlation between the 1H at 5.31 ppm and the 13C at 21.1 ppm. Note the green box describes the region of interest.

Logic#11HMBCMissingCorrelation_Solution1_Jan102011
The correlation between the methyl 1H at 2.15 ppm and 13C at 84.7 ppm (indicated by the purple arrow and the red bonds below) is a weak 4J coupling (also denoted as a W-coupling or M-coupling). The coupling arises from the individual methyl protons rotating and interacting through a W-relationship (or M-)with the carbon. This coupling is not evident for the methine 1H at 5.31 ppm and the 13C at 21.1 ppm.

Logic#11HMBCMissingCorrelation_Solution2_Jan102011
Thank you Serge for your comment.

2 Replies to “Logic Puzzle #11: Pairwise Correlation Confidence … Solution”

  1. Hi,
    I have a mixture of N-acylated hydantoins. I would like to confirm the regiochemistry of this. Please let me know what techniques should be used. i have planned to take HMBC. Do you suggest any other data worth considering. Thanks for this.
    Regards
    Marto

  2. Hello Marto,
    I would suspect HMBC and NOESY (or NOE) experiments may assist in determining the regiochemistry of hydantoins. I would definitely check the literature for the types of experiments used to characterize hydantoins.
    Regards,
    Arvin

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