Stereostructural behaviour of N–N atropisomers: Two conglomerate crystallisations and a crystallisation-induced deracemisation

Abstract

The solid state behaviour of a number of compounds which show hindered rotation around an N–N bond, in some cases leading to axial chirality is described. A diacyl hydrazine, bisanthranoly hydrazine, 1 crystallises in the chiral space group P212121, presenting an example of conglomerate crystallisation. A tetra-acyl hydrazine derived from lactic acid, 2, shows kinetic resolution by crystallisation, as of the two isomers observed in the solution NMR, only one crystallises, again in the space group P212121. Two cyclic acyl hydrazines in the form of biquinazolinones are studied: 2,2′diphenyl-3,3-biquinazolinone, 3 crystallises in the achiral space group Pbca, while 3,3′-dimethyl-2,2′-biquinazoline-4′-thio-4-one, 4 crystallises in the chiral space group P21 giving another example of a conglomerate crystallisation. The single crystal structures of each of the species have been compared to powder XRD data to confirm that the single crystal structures are representative of the bulk material.