Predicting the Spontaneous Chiral Resolution by Crystallization of a Pair of Flexible Nitroxide Radicals
Gourlay, Matthew D. Kendrick, John Leusen, Frank J.J.
Gourlay, Matthew D.
Kendrick, John
Leusen, Frank J.J.
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2008
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The separation of racemates into pure enantiomers through crystallization is an important industrial process. This study provides further validation of a novel, predictive approach for spontaneous resolution in which crystal structure prediction simulations are used to explore the relative stabilities of racemic solids versus enantiopure solids. 2-(4-Hydroxyphenyl)-2,5,5-trimethylpyrrolidine-1-oxy (compound 1) has previously been shown to be a racemic conglomerate, while a similar compound, 2-(3-hydroxyphenyl)-2,5,5-trimethylpyrrolidine-1-oxy (compound 2), was not. A conformational search using the Dreiding force field revealed 10 conformational minima for compound 1, and 20 for compound 2. Atomic charges were calculated using unrestricted DFT B3LYP 6-311G** optimized structures, and a crystal structure prediction was performed using the Dreiding force field, considering all low-energy gas-phase conformations and all relevant space groups. Analysis of the predicted crystal structures suggests that compound 1 is a racemic conglomerate, but compound 2 is not. This is in agreement with the experimental evidence.
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Gourlay, M.D., Kendrick, J. and Leusen, F.J.J. (2008). Predicting the Spontaneous Chiral Resolution by Crystallization of a Pair of Flexible Nitroxide Radicals. Crystal Growth Design. Vol. 8, No. 8, pp. 2899-2905.
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