The winner of the Bridged bicyclic molecule NMR challenge (published in volume 415 issue 24) is:
Mirsadra Molaei, Department of Pharmaceutical Chemistry, Semmelweis University, Budapest, Hungary.
The award entitles the winner to select a Springer book of their choice up to a value of €100,-.
Our Congratulations!
The Bridged bicyclic molecule NMR Challenge asked readers to identify isomers of bicyclo[2.2.1]alkane from the 1H-NMR spectrum [1]. The most deshielded protons with signals in the vicinity of 4.5 ppm are from protons located at the base of the bridge. The key difference between the two spectra is that one of them shows two triplets, while the other shows a triplet and a doublet (Fig. 1).
At this point, one has to remember the Karplus equation that describes the variation of the coupling constants between two hydrogen atoms as a function of the dihedral angle between them [2]. The magnitude of this coupling is generally smallest when the torsion angle is close to 90° and largest at angles of 0 and 180° (Fig. 2).
Figure 2 illustrates the dihedral angles between the epoxy bridge hydrogen atoms and their neighboring hydrogen atoms in endo- and exo-isomers. Hence, according to the Karplus equation, in the case of the endo-isomer, the proton at the base of the bridge (closer to CH2OH) position has more complex multiplicity than in the exo-isomer, as illustrated in Fig. 3.
Keeping this in mind, let us analyze the 1H-NMR spectra of these isomers (Fig. 1). So, as can be seen from Fig. 1, in the endo-isomer of the bicyclo[2.2.1]alkane, both 1H signals of hydrogen atoms at the base of the bridge (4.4…4.6 ppm) will appear as triplets (A, Fig. 1, left spectrum). At the same time, for the exo-isomer, they appear as one triplet and one doublet (B, Fig. 1, right spectrum).
References
Kozytskyi A, Bondarenko AV. Anal Bioanal Chem. 2023;415:5855–6.
Dalton L. Chem Eng News. 2003;81(51):37. https://doi.org/10.1021/cen-v081n036.p037.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Conflict of interest
The authors declare no competing interests.
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This article is the solution to the Analytical Challenge to be found at https://doi.org/10.1007/s00216-023-04887-1
Rights and permissions
About this article
Cite this article
Kozytskyi, A.V., Bondarenko, A.V. Solution to bridged bicyclic molecule NMR challenge. Anal Bioanal Chem 416, 1999–2000 (2024). https://doi.org/10.1007/s00216-024-05211-1
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00216-024-05211-1