Conformational analysis of nine designed flexible 1,2-diarylethanes with different substituents show syn conformation due to p-p interactions by 1 H NMR in solution, this carries over to the solid state for three compounds while two show anti conformation in the solid state by X-ray crystallography and the remaining compounds do not give diffraction quality crystals.
In the crystal structure of 1,1'-(1,3-propanediyl)bis(5-ethyl-6-methylthio-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-4-one), C(19)H(24)N(8)O(2)S(2), the pairs of pyrazolo[3,4-d]pyrimidine rings of the molecule stack between the heterocyclic rings, due to intramolecular pi-pi interactions. The substituted ethyl and methyl groups are comparable as far as intramolecular stacking is concerned.
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