Molecular interactions and chirality

- Alicyclic diols can hydrogen bond in many different ways and yield most interesting structures. In this thesis, eight C2-symmetric diols 48-50, 78, 79 and 81-83 were synthesized and their crystal structures were determined. No less than seven of these show unusual solid state behaviour: 48 and 78 are inclusion hosts; 49, 50 and 78 form doubly-stranded hydrogen-bonded ladder structures, where there is a strong preference for each strand to be homochiral; 78, 81 and 82 undergo self-resolution during recrystallization; and 83 forms chirally pure crystals (but the material is still racemic).- One of the favourable supramolecular synthons for hydroxy compounds is the (O-H)6 cycle of hydrogen bonds. When this cycle is formed by a racemic compound, its enantiomers alternate down-up-down etc. around the cycle. No case of an (O-H)6 cycle involving chirally pure hydroxy compounds is known. These observations indicate a strong preference for the (O-H)6 cycle being constructed from achiral or racemic molecules rather than from chirally pure hydroxyl compounds. Racemic (±)-48 and (±)-92 which are already known to form (O-H)6 cycles in the solid state were prepared in chirally pure form and their X-ray crystal structures determined. No (O-H)6 cycles were observed for these homochiral diols. These findings confirm that the (O-H)6 motif occurs only for achiral or racemic compounds.- Similarly, the edge-to-edge eight-membered aryl C-HN dimer involves either achiral molecules or those of opposite chirality. No chirally pure dimers of this type are reported. Racemic compounds 42-44 that are known to pack using the C-HN dimer were synthesized in chirally pure form. No edge-to-edge eight-membered aryl C-HN dimers were formed in the solid state. Hence this supramolecular synthon is only favoured for achiral or racemic compounds only.- Other major conclusions are that the cause of self-resolution is due to packing energy. In some cases it is likely that solvent choice, or solvent plus temperature selection, can be used to control self-resolution