J(F,H), J(C,H) and J(H,H) couplings involving the individual methyl group protons in 1,2,3,4-tetrachloro-5,6,7,8-tetrafluoro-9-methyltriptycene. Evidence of blue-shifting hydrogen bond
✍ Scribed by I. Czerski; K. Kamieńska-Trela; W. Koźmiński; T. Ratajczyk; S. Szymański; J. Wójcik
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 154 KB
- Volume
- 45
- Category
- Article
- ISSN
- 0749-1581
- DOI
- 10.1002/mrc.2099
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✦ Synopsis
Abstract
1,2,3,4‐tetrachloro‐5,6,7,8‐tetrafluoro‐9‐methyltriptycene was studied in NMR spectra at low temperatures where the methyl group dynamics is frozen. Values of ^5^J(^19^F,^1^H), ^1^J(^13^C,^1^H), and ^2^J(^1^H,^1^H) for the individual methyl protons were measured. They are in a fair agreement with the corresponding theoretical values calculated at a density functional theory (DFT) level. The ^5^J(^19^F,^1^H) couplings involve the peri‐F nucleus and occur via the ‘through space’ mechanism. Both the natural bond orbital analysis (at a HF level) and the observed pattern of ^1^J(^13^C,^1^H) coupling values corroborate occurrence in this molecule of intramolecular, blue‐shifting hydrogen bonds engaging the methyl hydrogens. The ‘through space’ ^5^J(^19^F,^1^H) couplings may indicate the routes of electron density transfers that escape detection by the natural bond analysis. A consideration of these effects can enrich the chemical intuition involving this specific sort of H‐bonds. Copyright © 2007 John Wiley & Sons, Ltd.