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Structure Elucidation

For more than a decade, ACD/Structure Elucidator has been used by industry and academic experts to help solve some of the toughest structure problems. Using data from various analytical techniques (NMR, MS, UV, and IR) Structure Elucidator can propose chemical structures that are consistent with ALL available analytical data. The computer-aided structure elucidation (CASE) software has been used time and time again to help solve unknown structures and to correct erroneous proposed structures. Read on to see our featured story highlighting the use of Structure Elucidator and be sure to return to this page every month where we will highlight a new compound of interest.

The Initial Challenge

In a 2011 publication, Kummerlöwe and co-workers1 investigated one of the products obtained by reacting an azide-containing 1,5-enyne in the presence of electrophilic iodine sources.

After thorough collection, analysis, and interpretation of a comprehensive collection of analytical data, the authors concluded that they were unable to elucidate the chemical structure of the unknown by classical spectroscopic means.

As a result, they proceeded with an attempt to solve the problem in an unconventional way by using Residual Dipolar Couplings (RDCs). The authors suggested 14 structures and selected the preferable one using RDC. The proposed structure based on RDC analysis is shown below:

This structure was confirmed by a combination of 2D INADEQUATE data and 15N labeling. Further analysis revealed 9 non-standard carbon-carbon connectivities represented in the figure above with solid pink arrows. In addition, two unusually long and unexpected 5 bond heteronuclear correlations (denoted with the dashed pink arrows) were observed in the HMBC spectrum. Based on these nonstandard correlations, contradictory 2D NMR data was the main cause preventing structure elucidation using a traditional approach.

The Evidence

The CASE (Computer Assisted Structure Elucidation) Investigation

Conclusions

In this example, the authors were unable to elucidate the structure with traditional means, due to extremely contradictory 2D NMR data. The authors were able to determine the correct structure from a list of candidates based on the Residual Dipolar Couplings. Using a CASE system has the added benefit of automatically generating all possible structural candidates, and as such Structure Elucidator was able to unambiguously generate the correct structure immediately when given all the available data.

1G. Kummerlöwe, B. Crone, M. Kretschmer, S. F. Kirsch, B. Luy, Angew Chem Int Ed Engl, 2011, 50, 2643.
2Kirill Blinov, Mikhail Elyashberg, Ryan Sasaki, Sergey Molodstov, and Antony Williams, Poster at SMASH 2011, Chamonix, France.

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