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15N NMR chemical shift in the characterisation of halogen bonding in solution
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry.ORCID iD: 0000-0003-0359-5970
2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

15N NMR chemical shift in the characterisation of halogen bonding in solution  

Sebastiaan B. Hakkert, Jürgen Gräfenstein and Mate Erdelyi*   

NMR chemical shift changes induced upon formation of non-covalent interactions have been used as sensitive and specific observables in the evaluation of weak chemical forces in solutions, among others of halogen bonding.1 1H NMR has high sensitivity yet a narrow chemical shift range, ca 10 ppm, resulting in small and thus difficult to measure chemical shift changes upon binding. In contrast, 13C NMR offers a wider shift range, ca 200 ppm, providing larger chemical shift changes upon weak binding to be detected; however, its low sensitivity limits its applicability. 19F NMR provides high sensitivity and a wide chemical shift range, ca 500 ppm, and hence is straightforwardly applicable on substances that possess a fluorine close to the halogen bond donor site,2 but is unfortunately often unavailable for real-life substances applied in medicinal chemistry, for example, typically missing fluorine substitution. 15N NMR despite its low sensitivity, which can be overcome by indirect detection experiments (HMBC), provides several advantages, such as an unusually wide chemical shift range, ca 900 ppm, and most importantly the detectability of halogen and hydrogen bonds directly at the Lewis base involved in the interaction. Accordingly, upon formation of a halogen bond with a nitrogen donor ligand typically 10-20 ppm,3 and for very strong interactions up to 100 ppm,4 15N chemical shift changes have been reported.  

In this project we have evaluated the capability of 15N NMR to describe halogen bonding interactions with respect to solvent and electronic effects, and the alteration of N-X bond lengths. The observations made for halogen bonds were compared to those obtained for analogous hydrogen bonding systems using the same nitrogen donor halogen/hydrogen bond acceptor. The experimental data obtained on an 800 MHz spectrometer was compared to and interpreted with the help of computational data (DFT).The observed chemical shift changes upon formation of halogen bonds were correlated to various descriptors to understand their origin. Based on the above data the scope and limitations of 15N NMR for detection and understanding of halogen bonding in solution will be discussed.

References

1. Bertrán, J. F.; Rodríguez, M. Org. Magn. Reson. 1979, 12, 92, 1980, 14, 244; 1981, 16, 79.

2. Metrangolo, P.; Panzeri, W.; Recupero F; Resnati, G. J. Fluorine Chem. 2002, 114, 27.

3. Castro-Fernandez, S.; Lahoz, I. R.; Llamas-Saiz, A. L.; Alonso-Gomez, J. L.; Cid, M. M.; Navarro-Vazquez, A. Org. Lett. 2014, 16, 1136; Puttreddy, R.; Jurcek, O.; Bhowmik, S.; Makela, T.; Rissanen, K. Chem. Commun. 2016, 52, 2338.

4. Carlsson, A.-C. C.; Grafenstein, J.; Budnjo, A.; Laurila, J. L.; Bergquist, J.; Karim, A.; Kleinmaier, R.; Brath, U.; Erdelyi, M. J. Am. Chem. Soc. 2012, 134, 5706

Place, publisher, year, edition, pages
2017.
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-372084OAI: oai:DiVA.org:uu-372084DiVA, id: diva2:1275332
Conference
Halogen Bonding in Supramolecular Chemistry, Faraday Discussion, Ottawa, Canada July 10-12, 2017.
Available from: 2019-01-05 Created: 2019-01-05 Last updated: 2019-01-07

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