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Chirality without Stereoisomers: Insight from the Helical Response of Bond Electrons |
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| Authors: | Tianlv Xu Xing Nie Shuman Li Yong Yang Herbert Früchtl Tanja van Mourik Steven R Kirk Martin J Paterson Yasuteru Shigeta Prof Samantha Jenkins |
| Institution: | 1. Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research and Key Laboratory of Resource, National and Local Joint Engineering Laboratory for New Petro-chemical Materials and Fine Utilization of Resources, College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha, Hunan, 410081 China;2. EaStCHEM School of Chemistry, University of Saint Andrews, North Haugh, St Andrews, Fife, KY16 9ST Scotland, United Kingdom;3. Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS UK;4. Center for Computational Sciences, University of Tsukuba, Tsukuba, 305-8577 Japan |
| Abstract: | The association between molecular chirality and helical characteristics known as the chirality-helicity equivalence is determined for the first time by quantifying a chirality-helicity measure consistent with photoexcitation circular dichroism experiments. This is demonstrated using a formally achiral SN2 reaction and a chiral SN2 reaction. Both the achiral and chiral SN2 reactions possess significant values of the chirality-helicity measure and display a Walden inversion, i. e. an inversion of the chirality between the reactant and product. We also track the chirality-helicity measure along the reaction path and discover the presence of chirality at the transition state and two intermediate structures for both reactions. We demonstrate the need for the chirality-helicity measure to differentiate between steric effects due to eclipsed conformations and chiral behaviors in formally achiral species. We explain the significance of this work for asymmetric synthetic reactions including the intermediate structures where the Cahn-Ingold-Prelog (CIP) rules cannot be used. |
| Keywords: | molecular chirality SN2 reaction Walden inversion next generation QTAIM asymmetric catalysis |