Conformational Studies of Substituted Chromans: Crystal Structures of 2,2′-(1E,1′E)-(2,3-Dimethylchroman-2,4-diyl)bis(Azan-1-yl-1-ylidene)bis(Methan-1-yl-1-ylidene)Diphenol (I) and 2,2′-(1E,1′E)-(2-Ethyl-3-Methylchroman-2,4-diyl)bis(Azan-1-yl-1-ylidene)bis(Methan-1-yl-1-ylidene)Diphenol (II)

The title compounds C25H24N2O3 (I) and C26H26N2O3 (II) crystallize in the triclinic space group P-1 with cell parameters a = 8.981(1), b = 9.933(1), c = 12.369(2) , alpha = 78.537(2), beta = 84.515(2), gamma = 73.561(2)degrees Z = 2 (I) and a = 11.4630(9), b = 12.955(1), c = 16.154(1) , alpha = 70.425(1), beta = 87.403(1), gamma = 71.850(1)A degrees, Z = 4 (II). In both compounds the phenolic groups in the Schiff base substituents form intramolecular hydrogen bonds with the imine nitrogen atoms thereby rendering these substituents nearly planar. A detailed analysis of the amount by which the heterocyclic ring deviates from planarity (extent of puckering) in these and a series of related molecules shows that the extent of the deviation is largely unaffected by the number, size and placement of substituents on this ring.