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Rotational dynamics in a crystalline molecular gyroscope by variable-temperature C-13 NMR, H-2 NMR, X-ray diffraction, and force field calculations

Khuong, T-AV, Dang, H, Jarowski, PD, Maverick, EF and Garcia-Garibay, MA (2007) Rotational dynamics in a crystalline molecular gyroscope by variable-temperature C-13 NMR, H-2 NMR, X-ray diffraction, and force field calculations Journal of the American Chemical Society, 129, 4. pp. 839-845.

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Abstract

A combination of solid-state C-13 CPMAS NMR, H-2 NMR, X-ray-determined anisotropic displacement parameters (ADPs), and molecular mechanics calculations were used to analyze the rotational dynamics of 1,4-bis[3,3,3-tris(m-methoxyphenyl)propynyl]benzene (3A), a structure that emulates a gyroscope with a p-phenylene group acting as a rotator and two m-methoxy-substituted trityl groups acting as a stator. The line shape analysis of VT C-13 CPMAS and broad-band H-2 NMR data were in remarkable agreement with each other, with rotational barriers of 11.3 and 11.5 kcal/mol, respectively. The barriers obtained by analysis of ADPs obtained by single-crystal X-ray diffraction at 100 and 200 K, assuming a sinusoidal potential, were 10.3 and 10.1 kcal, respectively. A similar analysis of an X-ray structure solved from data acquired at 300 K suggested a barrier of only 8.0 kcal/mol. Finally, a rotational potential calculated with a finite cluster model using molecular mechanics revealed a symmetric but nonsinusoidal potential that accounts relatively well for the X-ray-derived values and the NMR experimental results. It is speculated that the discrepancy between the barriers derived from low and high-temperature X-ray data may be due to an increase in anharmonicity, or to disorder, at the higher temperature values.

Item Type: Article
Authors :
NameEmailORCID
Khuong, T-AVUNSPECIFIEDUNSPECIFIED
Dang, HUNSPECIFIEDUNSPECIFIED
Jarowski, PDp.d.jarowski@surrey.ac.ukUNSPECIFIED
Maverick, EFUNSPECIFIEDUNSPECIFIED
Garcia-Garibay, MAUNSPECIFIEDUNSPECIFIED
Date : January 2007
Identification Number : https://doi.org/10.1021/ja064325c
Related URLs :
Depositing User : Symplectic Elements
Date Deposited : 17 May 2017 11:49
Last Modified : 17 May 2017 11:49
URI: http://epubs.surrey.ac.uk/id/eprint/832889

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