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oai:uvadoc.uva.es:10324/663842024-02-22T20:00:53Zcom_10324_28708com_10324_954com_10324_894com_10324_28542com_10324_952com_10324_1186com_10324_931col_10324_28709col_10324_28543col_10324_1404

Barbero San Juan, Héctor Meunier, Antoine Kotturi, Kondalarao Smith, Ashton Kyritsakas, Nathalie Killmeyer, Adam Rabbani, Ramin Nazimuddin, Md Masson, Eric 2024-02-22T13:39:56Z 2024-02-22T13:39:56Z 2020 Phys.Chem.Chem.Phys., 2020, 22, 20602-20611 1463-9076 https://uvadoc.uva.es/handle/10324/66384 10.1039/D0CP03285A 20602 36 20611 Physical Chemistry Chemical Physics 22 1463-9084 Producción Científica The torsional barriers along the Caryl–Caryl axis of a pair of isosteric disubstituted biphenyls were determined by variable temperature 1H NMR spectroscopy in three solvents with contrasted hydrogen bond accepting abilities (1,1,2,2-tetrachloroethane-d2, nitrobenzene-d5 and dimethyl sulfoxide-d6). One of the biphenyl scaffolds was substituted at its ortho and ortho′ positions with N′-acylcarbohydrazide groups that could engage in a pair of intramolecular N–H⋯O=C hydrogen bonding interactions at the ground state, but not at the transition state of the torsional isomerization pathway. The torsional barrier of this biphenyl was exceedingly low despite the presence of the hydrogen bonds (16.1, 15.6 and 13.4 kcal mol−1 in the three aforementioned solvents), compared to the barrier of the reference biphenyl (15.3 ± 0.1 kcal mol−1 on average). Density functional theory and the solvation model developed by Hunter were used to decipher the various forces at play. They highlighted the strong stabilization of hydrogen bond donating solutes not only by hydrogen bond accepting solvents, but also by weakly polar, yet polarizable solvents. As fast exchanges on the NMR time scale were observed above the melting point of dimethyl sulfoxide-d6, a simple but accurate model was also proposed to extrapolate low free activation energies in a pure solvent (dimethyl sulfoxide-d6) from higher ones determined in mixtures of solvents (dimethyl sulfoxide-d6 in nitrobenzene-d5). We are grateful to the National Science Foundation (grants CHE-1507321 and CHE-1905238), the American Chemical Society Petroleum Research Fund (grant 56375-ND4), the Roenigk Family Foundation and Ohio University for their continuing financial support. HB is also supported by a fellowship from the Alfonso Martin Escudero Foundation. NK thanks the University of Strasbourg and the CNRS for financial support. application/pdf eng Royal Society of Chemistry info:eu-repo/semantics/restrictedAccess http://creativecommons.org/licenses/by-nc-nd/4.0/ Royal Society of Chemistry Attribution-NonCommercial-NoDerivatives 4.0 Internacional Counterintuitive torsional barriers controlled by hydrogen bonding info:eu-repo/semantics/article info:eu-repo/semantics/submittedVersion https://pubs.rsc.org/en/content/articlelanding/2020/cp/d0cp03285a SI