Dihydrogen contacts observed by through-space indirect NMR coupling.

Martin Dračínský,Michal Buchta,Irena G Stará,Miloš Buděšínský,Ivo Starý,Olga L Malkina,Jana Vacek-Chocholoušová

doi:10.1039/c8sc02859a

Abstract

"Through-space" indirect spin-spin couplings between hydrogen atoms formally separated by up to 18 covalent bonds have been detected by NMR experiments in model helical molecules. It is demonstrated that this coupling can provide crucial structural information on the molecular conformation in solution. The coupling pathways have been visualised and analysed by computational methods. The conformational dependence of the coupling is explained in terms of orbital interactions.

Highlights

Unambiguous determination of a molecular structure by X-ray analysis has been central to many achievements in chemistry and biology.[1]
We report on the “through-space” scalar coupling (TSC) between hydrogen nuclei, which may be used for accurate determination of molecular conformation
According to the classic theory of Ramsey,[59] four different terms contribute to the indirect spin–spin coupling: the Fermi contact (FC, usually the most important), spin–dipole (SD), paramagnetic spin–orbit (PSO), and diamagnetic spin–orbit (DSO) terms

Summary

Introduction

Unambiguous determination of a molecular structure by X-ray analysis has been central to many achievements in chemistry and biology.[1]. Most of the interesting behaviour of molecules takes place in solution, raising the question of whether, and how much, the molecular structures in crystal and solution really resemble each other This can be an issue for molecules exhibiting signi cant conformational freedom, as solvation and crystal packing may affect their structure.[2,3]. Helicenes and their analogues[4,5,6,7,8,9,10,11,12,13,14,15] illustrate this problem well. Recent theoretical studies showed that the helix pitch of helicenes, which might, in principle, be tuned by applying an external mechanical force, dramatically in uences the single molecule conductivity,[19,20] piezoelectric properties,[21] and thermopower efficiency.[22]

Methods

Results

Conclusion