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Molecules 2018, 23(9), 2294; https://doi.org/10.3390/molecules23092294

Electronic Effect on the Molecular Motion of Aromatic Amides: Combined Studies Using VT-NMR and Quantum Calculations

1
Department of Chemistry, Chung-Ang University, Seoul 156-756, Korea
2
Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Korea
3
Department of Chemistry, Korea University, Seoul 02841, Korea
4
Nuclear Chemistry Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea
5
Department of Chemistry, Korea Military Academy, Seoul 01805, Korea
*
Authors to whom correspondence should be addressed.
Received: 6 August 2018 / Revised: 4 September 2018 / Accepted: 4 September 2018 / Published: 8 September 2018
(This article belongs to the Special Issue Amide Bond Activation)
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Abstract

Rotational barrier energy studies to date have focused on the amide bond of aromatic compounds from a kinetic perspective using quantum calculations and nuclear magnetic resonance (NMR). These studies provide valuable information, not only regarding the basic conformational properties of amide bonds but also the molecular gear system, which has recently gained interest. Thus, we investigate the precise motion of the amide bonds of two aromatic compounds using an experimental rotational barrier energy estimation by NMR experiments and a theoretical evaluation of the density functional theory calculation. The theoretical potential energy surface scan method combined with the quadratic synchronous transit 3 method and consideration of additional functional group rotation with optimization and frequency calculations support the results of the variable temperature 1H NMR, with deviations of less than 1 kcal/mol. This detailed experimental and theoretical research strongly supports molecular gear motion in the aromatic amide system, and the difference in kinetic energy indicates that the electronic effect from the aromatic structure has a key role in conformational movements at different temperatures. Our study provides an enhanced basis for future amide structural dynamics research. View Full-Text
Keywords: rotational barrier energy; amide bond; nuclear magnetic resonance; kinetic; density functional theory rotational barrier energy; amide bond; nuclear magnetic resonance; kinetic; density functional theory
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Kim, S.; Kim, J.; Kim, J.; Won, D.; Chang, S.-K.; Cha, W.; Jeong, K.; Ahn, S.; Kwak, K. Electronic Effect on the Molecular Motion of Aromatic Amides: Combined Studies Using VT-NMR and Quantum Calculations. Molecules 2018, 23, 2294.

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