CLVII.—Isomerism of p-azophenol

Effect of Methyl, Hydroxyl, and Chloro Substituents in Position 3 of 3′,4′,7‐Trihydroxyflavylium: Stability, Kinetics, and Thermodynamics

“…This compound was prepared according to a procedure reported in the literature for a similar compound, 2,4′‐diacetoxyacetophenone . Potassium acetate (14.3 mmol, 1.4 g) was added to a stirred solution of 2‐chloro‐3′,4′‐dihydroxyacetophenone (10.7 mmol, 2.0 g) in acetic anhydride (20 mL).…”

X-Ray crystallography and the chemistry of the steroids. Part I

“…X-ray analysis of any crystalline material can yield, according to the degree to which it is pushed, a succession of data bearing in greater and greater detail on the structure of the material. Briefly, the successive stages of analysis can yield information on: I, Identification and comparison of substances from different sources; II, Molecular weight to any desired degree of accuracy; III, Symmetry of molecules; IV, General size and shape of molecules; V, Position of substituent groups; VI, Position of all the atoms in the molecules (Crowfoot and Bernal 1937;Robertson 1937). The first three stages are straightforward and unequivocal, the next two are less direct and usually require a degree of collaboration between crystallographic and chemical methods.…”

“…Examples of both varieties of interaction are well known already in the crystal structures of oxalic acid and oxalic acid dihydrate (Hendricks 1935;Robertson 1936). Among the sterols the first process seems frequently attended by some difficulty, witness the extremely com plicated structures of anhydrous cholesterol and ergosterol and the great readiness with which crystals, particularly of the latter and many closely related sterols, take up water or alcohol of crystallization.…”

X-ray analysis of hydrogen bonding in the structure of oxalic acid dihydrate

“…In oxalic acid dihydrate this possibility takes a particular form. The earliest structure determinations, such as those by Zachariasen (1934) and by Robertson & Woodward (1936), indicated that the water molecule was bound to the hydroxyl group and to two neighbouring carbonyl groups. What remained uncertain was whether a more or less symmetrical oxonium ion was thereby formed~ as Zachariasen had proposed and Bernal & Megaw (1935) afterwards disputed.…”