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Chirality and Achirality in Crystal Structures H. D. Flack and G. Bernardinelli University of Geneva, Switzerland www.flack.ch/howard/cristallo/publcns.html
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L- and D- quartz
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Chirality in Chemistry
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Hans Erni’s drawing
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Kelvin’s definition of chirality
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Lord Kelvin
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Modern definitions of Chirality IUPAC: The geometric property of a rigid object (or spatial arrangement of point or atoms) of being non-superposable by pure rotation and translation on its image formed by inversion through a point; the symmetry group of such an object contains no symmetry operations of the second kind ( 1, m, 3, 4, 6). When the object is superposable by pure rotation and translation on its inverted image, the object is described as being achiral; the symmetry group of such an object contains symmetry operations of the second kind. Barron: True chirality is exhibited by systems that exist in two distinct enantiomorphic states that are interconverted by space inversion by not by time reversal combined with any proper spatial rotation.
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes CA NC NA
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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Optical activity in crystals and molecules Single crystal Molecules gas or liquid Achiral m, mm2, 4, 42m: Yes Other point groups: No No ChiralYes Enantiopure: Yes Racemate: No Enantiomeric mixture: Yes
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Useful terms Enantiomorph: One of a pair of chiral objects or models of opposite chirality sense. Enantiomer: One of a pair of chiral molecular entities of opposite chirality sense. Racemate: An equimolar mixture of a pair of enantiomers. IUPAC Basic Terminology of Stereochemistry http://www.chem.qmul.ac.uk/iupac/stereo/
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Crystal structures formed from chiral and achiral molecules Achiral crystal structure Chiral crystal structure Achiral molecules Chiral molecules enantiopure Chiral molecules racemate Chiral molecules enantiomeric mixture
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Crystal structures formed from chiral and achiral molecules Achiral crystal structure Chiral crystal structure Achiral molecules permitted Chiral molecules enantiopure Chiral molecules racemate Chiral molecules enantiomeric mixture
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Crystal structures formed from chiral and achiral molecules Achiral crystal structure Chiral crystal structure Achiral molecules permitted Chiral molecules enantiopure Chiral molecules racemate Chiral molecules enantiomeric mixture
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Crystal structures formed from chiral and achiral molecules Achiral crystal structure Chiral crystal structure Achiral molecules permitted Chiral molecules enantiopure forbidden Chiral molecules racemate Chiral molecules enantiomeric mixture
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Crystal structures formed from chiral and achiral molecules Achiral crystal structure Chiral crystal structure Achiral molecules permitted Chiral molecules enantiopure forbiddenpermitted Chiral molecules racemate Chiral molecules enantiomeric mixture
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Crystal structures formed from chiral and achiral molecules Achiral crystal structure Chiral crystal structure Achiral molecules permitted Chiral molecules enantiopure forbiddenpermitted Chiral molecules racemate permitted Chiral molecules enantiomeric mixture
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Crystal structures formed from chiral and achiral molecules Achiral crystal structure Chiral crystal structure Achiral molecules permitted Chiral molecules enantiopure forbiddenpermitted Chiral molecules racemate permitted Chiral molecules enantiomeric mixture
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( ) o-tyrosine
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Crystal structures formed from chiral and achiral molecules Achiral crystal structure Chiral crystal structure Achiral molecules permitted Chiral molecules enantiopure forbiddenpermitted Chiral molecules racemate permitted Chiral molecules enantiomeric mixture like enantiopure?
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Idealized binary phase diagrams for enantiomeric mixtures
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Conglomerate - phase diagram
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Racemic structure formation – phase diagram
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-(1-naphthoxy) propionic acid & -(1-naphthyl) propionic acid
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m-fluoromandelic acid & m-chlorophenyl hydracylic acid
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Free energy vs temperature
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Solid solution formation
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Methyprylon
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Methyprylon 3D
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Crossing isodimorphism with two minima
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Melting point diagram of methyprylon
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Methyprylon cell dimensions and optical activity Einem glücklichen Zufall ist zu verdanken, dass in der Fraktion A beide Modifikationen entdeckt wurden.
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Solid solution formation
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Frederic Stanley Kipping 1863 - 1949
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Prelog’s L- and D- quartz
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Brazil twin of quartz
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Hexahelicene From racemic solutionFrom enantiopure solution
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Characterisation of enantiomers for absolute configuration determination Optical activity CD spectrum (circular dichroism) Enantioselective (chiral) chromatography
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E. P. Kündig, M. Kondratenko, F. Robvieux, G. Bernardinelli, (2003). Organometallics, 22, - Space group P2 1 2 1 2 1 ; crystals grown from racemate; refinements using the above configuration: Crystal 1: Flack parameter x = 0.36(4); ee = 28(8)% Crystal 2: Flack parameter x = 0.90(3); ee = -80(6)% CD spectra, from crystal 1 and crystal 2 in solution, normalised to allow for the volume of the crystal.
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E. P. Kündig, M. Kondratenko, F. Robvieux, G. Bernardinelli, (2003). Organometallics, 22, - ee(x-ray) / ee(x-ray) = -0.35(10); CD(350) / CD(350) = -0.42
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P. Müller, D. Riegert, G. Bernardinelli, (2003). Helv. Chim. Acta 86, - Space group P2 1 ; Flack parameter x = -0.03(12) CD spectrum flat; [ ] D = 0.7 Substance ee = 43%, semi-preparative separation by HPLC Enantiomer composing the single crystal used for X-ray diffraction was unequivocally identified by HPLC.
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1 2/m mmm 4/mmm 3m 6/mmm (m 3m) 4/m 3 6/m (m 3) 222 422 32 622 23 432 1 2 4 3 6 4mm 3m 6mm m mm2 4 42m 6 6m2 43m 32 geometric crystal classes
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Anti-wurtzite Mn 1–y Fe y S, y 0.05; P6 3 mc; Flack parameter x = 0.02(4) “... is found to crystallize in the inverse wurtzite structure, i.e. the wurtzite-type structure but with the opposite absolute configuration, which can be named anti-wurtzite.” Point group 6mm contains symmetry operations of the second kind, e.g. m. The crystal structure is achiral. There is no ‘opposite absolute configuration’. Anti-wurtzite is just wurtzite in another orientation.
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Anti-wurtzite Model for Flack parameter: C = (1-x) X + x X. The macroscopic crystal C is treated as a mixture of an oriented crystal structure X and its inverted structure X in variable proportion. Point group 6mm contains symmetry operations of the second kind, e.g. m. The crystal structure is achiral. X and X are not identical but may be brought into congruence by making a pure rotation.
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Symmetry elements in point groups 6/mmm and 6mm International Tables for Crystallography Vol. A 6/mmm6mm
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Point groups 6/mmm and 6mm
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1 6 3 2 [001] 3 2 6 5 m [100] m [210] m [110] m [120] m [010] m [ 110] 2 [100] 2 [ 110] 2 [010] 2 [120] 2 [110] 2 [210] 1 6 5 3 5 m [001] 3 6
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Point groups 6/mmm and 6mm 1 6 3 2 [001] 3 2 6 5 m [100] m [210] m [110] m [120] m [010] m [ 110] 6/mmm 2 [100] 2 [ 110] 2 [010] 2 [120] 2 [110] 2 [210] 1 6 5 3 5 m [001] 3 6
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Point groups 6/mmm and 6mm 1 6 3 2 [001] 3 2 6 5 m [100] m [210] m [110] m [120] m [010] m [ 110] 6mm 6/mmm 2 [100] 2 [ 110] 2 [010] 2 [120] 2 [110] 2 [210] 1 6 5 3 5 m [001] 3 6
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Point groups 6/mmm and 6mm 1 6 3 2 [001] 3 2 6 5 m [100] m [210] m [110] m [120] m [010] m [ 110] 6mm 6/mmm 2 [100] 2 [ 110] 2 [010] 2 [120] 2 [110] 2 [210] 1 6 5 3 5 m [001] 3 6
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Point groups 6/mmm and 6mm 2 [100] 2 [ 110] 2 [010] 2 [120] 2 [110] 2 [210] 1 6 5 3 5 m [001] 3 6
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Equivalent twin operations for 6mm in 6/mmm 2 [100] 2 [ 110] 2 [010] 2 [120] 2 [110] 2 [210] 1 6 5 3 5 m [001] 3 6
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Achiral crystal structures formed from enantiopure molecules Achiral crystal structure Chiral crystal structure Achiral molecules Chiral molecules enantiopure forbidden Chiral molecules racemate Chiral molecules enantiomeric mixture
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La Coupe du Roi
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The End On ne peut être trop prudent dans les conclusions à déduire de l’expérience, lorsque l’on a affaire à des substances quelquefois si semblables en apparence, et qui peuvent être au fond si différentes. Louis Pasteur (1848)
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