X-ray studies of reactions in organic solids

Abstract

Correlations of the chemical structures of products from organic solid state reactions with the molecular packing in the reactant crystal structures define the extent of lattice restraints on molecular motion before and during reaction. The molecular behaviour after the chemical transition state can be inferred from comparisons of the molecular orientations in the initial and final phases. The formation of preferentially oriented product phases suggests that highly specific geometrical mechanisms are operative but additional criteria are needed to establish a direct correspondence between specific reactant and product molecules. Observable intermediate mesomorphic phases are particularly useful in defining the directions in which crystallographic order is not preserved. Several studies of hydrolysis, isomerization and polymerization reactions suggest surprisingly large molecular migrations and conformational changes may occur without randomizing the total distribution of product molecules. Competing and consecutive transformations often give rise to several simultaneously present and mutually oriented product phases and, in some cases, large molecular moieties of the initial structure do not appear in any of the final ordered phases. Novel twinning frequently is observed when degenerate transformation mechanisms give rise to several preferred orientations of product structures which cannot reorganize to form a single phase of long-range order. While the short-range molecular arrangement in the oriented product phase usually is identical with that produced during conventional crystallizations, exceptions may be found in the formation of chemically unstable molecular structures or metastable polymorphs of the product phase.

A kinetic and x-ray diffraction study of the solid state rearrangement of methyl p-dimethylaminobenzenesulfonate. Reaction rate enhancement due to proper orientation in a crystal

“…Additional powder patterns taken after 2,5,6,8,11, and 33 days were used to photographically follow the rearrangement process, and the d values from representative patterns are given in Table V. In the first two columns are shown the values observed for MSE, along with those calculated from the single crystal atomic parameters.…”

“…Sulfonyl chloride (1.97 g) (11) was dissolved in 20 ml of dry (distilled from KOH) pyridine in a 50-1111 round-bottom flask. n-Butanol (0.9 ml, 0.7 g) was added, and the reaction was covered with a drying tube and stored in the refrigerator for 3 days.…”

“…pDimethylaminobenzenesulfony1 Chloride (11). A 1000-ml threeneck 24/40 round-bottom flask equipped with N2 inlet, reflux condensor, mechanical stirrer, and 25-ml addition funnel was charged with 38 g of I (freshly dried at 80 OC under high vacuum) and 410 ml of freshly distilled dry benzene.…”

Photochemical Mechanism in Single Crystals: FTIR Studies of Diacyl Peroxides

“…Spatial averaging means that minor components of the crystal appear superimposed on the host structure, so that it is quite challenging to pick out reaction intermediates or products in concentrations of a few percent, even if they are all identically oriented. In some cases product structures have been determined in situ, but often the mechanistic connection between initial and final geometries is not obvious, especially if the shape or symmetry of the unit cell changes [35].…”

Hypervalent halogen compounds

“…The ylides 91 It is noteworthy that 2-diazodimedone and 2-dimethylsulphoniodimedonate are inert to diphenylketene under the same reaction conditions, a fact which may reflect the higher reduction potentials of the diazonium and dimethylsulphonium functions in the intermediate betaines. The phenylation of a variety of carbanions with diaryliodonium salts has been observed and is believed to involve a similar electrontransfer p r o~e s s~~~-~~' .…”