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Open AccessArticle

H/D Isotope Effects on 1H-NMR Chemical Shifts in Cyclic Heterodimers and Heterotrimers of Phosphinic and Phosphoric Acids

1
Institute of Chemistry, St. Petersburg State University, Universitetskij pr. 26, 198504 St. Petersburg, Russia
2
Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie str., 50-383 Wrocław, Poland
*
Author to whom correspondence should be addressed.
Academic Editor: Poul Erik Hansen
Molecules 2020, 25(8), 1907; https://doi.org/10.3390/molecules25081907
Received: 27 March 2020 / Revised: 15 April 2020 / Accepted: 19 April 2020 / Published: 20 April 2020
(This article belongs to the Special Issue Isotope Effects 2019)
Hydrogen-bonded heterocomplexes formed by POOH-containing acids (diphenylphosphoric 1, dimethylphosphoric 2, diphenylphosphinic 3, and dimethylphosphinic 4) are studied by the low-temperature (100 K) 1H-NMR and 31P-NMR using liquefied gases CDF3/CDF2Cl as a solvent. Formation of cyclic dimers and cyclic trimers consisting of molecules of two different acids is confirmed by the analysis of vicinal H/D isotope effects (changes in the bridging proton chemical shift, δH, after the deuteration of a neighboring H-bond). Acids 1 and 4 (or 1 and 3) form heterotrimers with very strong (short) H-bonds (δH ca. 17 ppm). While in the case of all heterotrimers the H-bonds are cyclically arranged head-to-tail, ···O=P–O–H···O=P–O–H···, and thus their cooperative coupling is expected, the signs of vicinal H/D isotope effects indicate an effective anticooperativity, presumably due to steric factors: when one of the H-bonds is elongated upon deuteration, the structure of the heterotrimer adjusts by shortening the neighboring hydrogen bonds. We also demonstrate the formation of cyclic tetramers: in the case of acids 1 and 4 the structure has alternating molecules of 1 and 4 in the cycle, while in case of acids 1 and 3 the cycle has two molecules of 1 followed by two molecules of 3. View Full-Text
Keywords: phosphinic acids; phosphoric acids; hydrogen bond; heterodimers; heterotrimers; heterotetramers; H/D isotope effects; NMR phosphinic acids; phosphoric acids; hydrogen bond; heterodimers; heterotrimers; heterotetramers; H/D isotope effects; NMR
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MDPI and ACS Style

Mulloyarova, V.V.; Ustimchuk, D.O.; Filarowski, A.; Tolstoy, P.M. H/D Isotope Effects on 1H-NMR Chemical Shifts in Cyclic Heterodimers and Heterotrimers of Phosphinic and Phosphoric Acids. Molecules 2020, 25, 1907.

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