A multinuclear NMR investigation of the effect of tert-butyl substituents on the rotation of the pyridine ring in acid solutions

文献情報

出版日

DOI 10.1039/A904339J

インパクトファクター 3.676

著者

原文を見る

要旨

The line-shape of the NMR signals of protons bonded to nitrogen indicated that the longitudinal relaxation of 14N is much faster for di-tert-butylpyridinium ions (DTBPH+) than for pyridinium (PyH+) in solution. Computer modeling showed ratios of relaxation times (T1=1/R1) of 10–20. A significant difference between the relaxation times (T1=1/R1) for the carbon atoms in β and γ positions (4.71 and 4.75 s for PyH+, 0.55 and 0.79 s for DTBPH+) was observed as well. Thus, the difference in longitudinal relaxation rates originates in a different rate of tumbling in solution, rather than a difference in the electrical field gradient. Calculations of the correlation times for the relaxation of molecules considered as ellipsoid-shape rotors in a medium of given viscosity indicate that the difference in size covers only a part of the difference in tumbling rates (lower τc for pyridine). The rest comes from specific interactions with the solvent, in the form of electrical double layers which have to be disturbed during the rotation. For PyH+, this electrical friction decreases when the acid strength increases, whereas for DTBPH+ the opposite effect is observed.

掲載誌

Physical Chemistry Chemical Physics

CiteScore: 5.5

自己引用率: 10.3%

年間論文数: 3036

Physical Chemistry Chemical Physics (PCCP) is an international journal co-owned by 19 physical chemistry and physics societies from around the world. This journal publishes original, cutting-edge research in physical chemistry, chemical physics and biophysical chemistry. To be suitable for publication in PCCP, articles must include significant innovation and/or insight into physical chemistry; this is the most important criterion that reviewers and Editors will judge against when evaluating submissions. The journal has a broad scope and welcomes contributions spanning experiment, theory, computation and data science. Topical coverage includes spectroscopy, dynamics, kinetics, statistical mechanics, thermodynamics, electrochemistry, catalysis, surface science, quantum mechanics, quantum computing and machine learning. Interdisciplinary research areas such as polymers and soft matter, materials, nanoscience, energy, surfaces/interfaces, and biophysical chemistry are welcomed if they demonstrate significant innovation and/or insight into physical chemistry. Joined experimental/theoretical studies are particularly appreciated when complementary and based on up-to-date approaches.