RT info:eu-repo/semantics/article
T1 Counterintuitive torsional barriers controlled by hydrogen bonding
A1 Barbero San Juan, Héctor
A1 Meunier, Antoine
A1 Kotturi, Kondalarao
A1 Smith, Ashton
A1 Kyritsakas, Nathalie
A1 Killmeyer, Adam
A1 Rabbani, Ramin
A1 Nazimuddin, Md
A1 Masson, Eric
AB 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).
PB Royal Society of Chemistry
SN 1463-9076
YR 2020
FD 2020
LK https://uvadoc.uva.es/handle/10324/66384
UL https://uvadoc.uva.es/handle/10324/66384
LA eng
NO Phys.Chem.Chem.Phys., 2020, 22, 20602-20611
NO Producción Científica
DS UVaDOC
RD 13-may-2024