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Phys Chem Chem Phys. 2017 Jan 25;19(4):2900-2907. doi: 10.1039/c6cp07552e.

Internal dynamics in helical molecules studied by X-ray diffraction, NMR spectroscopy and DFT calculations.

Author information

1
Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo 2, 16610 Prague, Czech Republic. dracinsky@uochb.cas.cz.
2
Institute of Chemical Process Fundamentals, Czech Academy of Sciences, Rozvojová 135, 16502 Prague, Czech Republic. sykora@icpf.cas.cz.
3
Faculty of Science, Charles University in Prague, Hlavova 2030, 12840 Prague, Czech Republic.

Abstract

The conformational behaviour of a prototype helical molecule, [6]helicene, and its derivatives was studied in solution and the solid state. Available crystal structures of [6]helicene revealed surprisingly large flexibility of this molecule and variable-temperature NMR experiments provided unusual temperature dependence of chemical shifts of hydrogen, carbon and fluorine atoms in the peripheral aromatic rings of [6]helicene and tetrafluoro[6]helicene. These chemical shift changes were interpreted as a consequence of the helicene 'pitch' opening with elevated temperature, and the experimental data were corroborated by DFT calculations of the chemical shift dependence on the helicene conformation and by variable-temperature DFT molecular dynamics simulations.

PMID:
28079219
DOI:
10.1039/c6cp07552e

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