19 Kryptoracemates
385
Figure 19.2 shows images for 4-azido-5-(biphenyl-4-yl)-5-hydroxy-3-methyl2-oxo-2,5-dihydrofuran (2), a neutral molecule crystallising with Z
= 2 (spacegroup P2 1 ); the R-form is illustrated in the molecular diagram [22]. The overlap
diagram highlights a close correspondence of the molecular structures in the independent tetrahydrofuranyl rings (R-form and inverted S-form) but differences in the
orientations of the biphenyl residues.
In 3, 2,4-dinitro-2,3-dichloro-3-thiolene-1,1-dioxide, rich in heteroatoms, a close
overlap is again noted between the five-membered rings when the molecule in
Fig. 19.3, i.e. the S-form, is overlapped with the inverted form [23]. The molecule
crystallises in the orthorhombic space-group P2 1 2 1 2 1 with Z
= 2.
Kryptoracemic behaviour is not restricted to examples with Z
= 2, i.e. two independent molecules in the crystallographic asymmetric unit. This is illustrated for
1,6-dihydro-1,6-dimethyl-4-phenyl-1,2,3-triazine 2-oxide (4), where Z
= 4 (monoclinic, P2 1 ); 4 is another example of a formally charged species [24]. The asymmetric
Fig. 19.2 Images for 4-azido-5-hydroxy-3-methyl-5-(4-phenylphenyl)-2,5-dihydrofuran-2-one
(DIXPUW), 2: chemical diagram, molecular structure and overlay diagram
Fig. 19.3 Images for
2,3-dichloro-2,4-dinitro-2,5dihydro-1λ 6 -thiophene-1,1dione (LACFEB), 3:
chemical diagram, molecular
structure and overlay
diagram
385
Figure 19.2 shows images for 4-azido-5-(biphenyl-4-yl)-5-hydroxy-3-methyl2-oxo-2,5-dihydrofuran (2), a neutral molecule crystallising with Z
= 2 (spacegroup P2 1 ); the R-form is illustrated in the molecular diagram [22]. The overlap
diagram highlights a close correspondence of the molecular structures in the independent tetrahydrofuranyl rings (R-form and inverted S-form) but differences in the
orientations of the biphenyl residues.
In 3, 2,4-dinitro-2,3-dichloro-3-thiolene-1,1-dioxide, rich in heteroatoms, a close
overlap is again noted between the five-membered rings when the molecule in
Fig. 19.3, i.e. the S-form, is overlapped with the inverted form [23]. The molecule
crystallises in the orthorhombic space-group P2 1 2 1 2 1 with Z
= 2.
Kryptoracemic behaviour is not restricted to examples with Z
= 2, i.e. two independent molecules in the crystallographic asymmetric unit. This is illustrated for
1,6-dihydro-1,6-dimethyl-4-phenyl-1,2,3-triazine 2-oxide (4), where Z
= 4 (monoclinic, P2 1 ); 4 is another example of a formally charged species [24]. The asymmetric
Fig. 19.2 Images for 4-azido-5-hydroxy-3-methyl-5-(4-phenylphenyl)-2,5-dihydrofuran-2-one
(DIXPUW), 2: chemical diagram, molecular structure and overlay diagram
Fig. 19.3 Images for
2,3-dichloro-2,4-dinitro-2,5dihydro-1λ 6 -thiophene-1,1dione (LACFEB), 3:
chemical diagram, molecular
structure and overlay
diagram