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The impact of the π‐electron conjugation on 15 N, 13 C and 1 H NMR chemical shifts in push–pull benzothiazolium salts. Experimental and theoretical study
Author(s) -
Hrobárik Peter,
Horváth Branislav,
Sigmundová Ivica,
Zahradník Pavol,
Malkina Olga L.
Publication year - 2007
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2074
Subject(s) - chemistry , chemical shift , conjugated system , iodide , carbon 13 nmr , nmr spectra database , nuclear magnetic resonance spectroscopy , nitrogen , moiety , density functional theory , computational chemistry , spectral line , stereochemistry , inorganic chemistry , organic chemistry , physics , astronomy , polymer
The 15 N as well as 13 C and 1 H chemical shifts of eight push–pull benzothiazolium iodides with various π‐conjugated chains between dimethylamino group and benzothiazolium moiety have been determined by NMR spectroscopy at the natural‐abundance level of all nuclei in DMSO‐ d 6 solution. In general, the quaternary benzothiazolium nitrogen is more shielded [δ( 15 N‐3) vary between − 241.3 and − 201.9 ppm] with respect to parent 3‐methylbenzothiazolium iodide [δ( 15 N‐3) = − 183.8 ppm], depending on the length and constitution of the π‐conjugated bridge. A larger variation in 15 N chemical shifts is observed on dimethylamino nitrogen, which covers the range of − 323.3 to − 257.2 ppm. The effect of π‐conjugation degree has a less pronounced influence on 13 C and 1 H chemical shifts. Experimental data are interpreted by means of density functional theory (DFT) calculations. Reasonable agreement between theoretical and experimental 15 N NMR chemical shifts was found, particularly when performing calculations with hybrid exchange‐correlation functionals. A better accord with experiment is achieved by utilizing a polarizable continuum model (PCM) along with an explicit treatment of hydrogen‐bonding between the solute and the water present in dimethylsulfoxide (DMSO). Finally, 13 C and 1 H NMR spectra were computed and analysed in order to compare them with available experimental data. Copyright © 2007 John Wiley & Sons, Ltd.