G. M. J. Schmidt

The crystal structure of [18]annulene, I. X‐ray study

effects are negligible and these two models differ only in this respect. The differences are essentially zero. (The small deviation from zero of the plotted differences at low atomic number arises for the most part from small inaccuracies in the analytic fits used to compute the differences). At the higher atomic numbers the difference is always negative because the relativistic DS atomic model is more compact than the nonrelativistic HFS model. As a general rule, the inclusion of exchange has a greater effect on the scattering factors than does relativity. At the heaviest elements the two effects appear to be comparable.

Excimer emission and photodimerization in a crystalline stilbene

Abstract Crystalline 2,4-dichloro- trans -stilbene (II) displays excimer emission and undergoes photoreaction to yield the mirror-symmetric dimer 1, cis -2-di(2, 4-dichlorophenyl)- trans -3, tarans -4-diphenlcyclobutane (III). In solution, under a variety of conditions. II shows only monomer emission and yields, in addition to III, the centric photodimer 1, trans -3-di(2,4-dichlorophenyl)- cis -2, trans -4-diphenylcyclcbutane (IV) and cis -monomer.

Shock-induced irreversible phase transitions in inorganic solids

Abstract A technique for the toroidally symmetrical implosion of non-metallic solids has been developed, and satisfactory recovery of shocked materials achieved. A procedure to quench a heat-sensitive high-pressure phase produced by a pressure pulse has been demonstrated. New examples of shock-induced phase changes have been found in the reconstructive transitions litharge → massicot,β → α lead dioxide, and cadmium sulfide (wurtzite → zincblende via the sodium chloride structure). A shock-induced ionic displacement transition has been observed in calcite → aragonite. By analogy with static experiments involving shear it is concluded that both types of phase transitions obtained here by the converging shockwave technique take place by a shear mechanism.

Topochemistry. Part XXXI. Formation of cyclo-octa-1,5-cis,cis-dienes from 1,4-disubstituted s-trans-butadienes in the solid state. A contribution to the problem of C4-versus C8-cyclodimerisation

Solid penta-1,3-diene-1-carboxylic acid (4), penta-1,3-diene-1-carboxamide (5), buta-1,3-diene-1,4-dicarbonitrile (6), styrylacrylic acid (10), its methyl ester (46), and amide (49)(all trans,trans-configurated), all photodimerise on irradiation (λ > 290 nm), to divinylcyclobutane (C4) derivatives. The structures of the fully characterised photoproducts from (4), (5), (6), and (49) and the light-stability of (N-phenyl)styrylacrylamide (53), are predictable from the known or postulated packing arrangements of their monomers.Cyclo-octa-1,5-trans,trans-dienes, although topochemically and symmetry-allowed from monomers which crystallise with parallel butadiene chains [(4), (5), (6), and possibly (10)], are not observed. Although the formation of C8-cyclodimers cannot be rigorously excluded our results neither support nor require their presence.The (all-ax)-cyclo-octa-1,5-cis,cis-diene (C8) derivatives formed during irradiation of (4), (5), and (10) are not primary photoproducts but arise from thermal (Cope) rearrangements of photochemically produced cis-1,2-divinylcyclobutanes.

TOPOCHEMISTRY I THE PHOTOTROPY OF ANILS

Abstract The results of the experiments with rigid solvents suggest that the requirement for photo-colourability is an intra-molecular hydrogen bond and the existence of the corresponding quinonoid form. This and the crystallographic classification indicate that the distinction between phototropic and non-phototropic salicylal anils lies in an intra- vs. inter-molecular hydrogen bond. The structures of representative anils are discussed in this connection. There is evidence that the changes in the positions of atoms, other than hydrogen, which accompany the colour change, are very small.

Photoreactions of di-p-anisylidenefulgide (di-p-anisylidenesuccinic anhydride)

The title compound as synthesised is the trans,trans-isomer. It is converted photochemically in solution to the cis,trans- and cis,cis-isomers. Irradiation of crystals of the cis,trans-form leads back to the trans,trans-, whereas irradiation of solid cis,cis- gives rise to other products.

Reactions in emulsions—I: The rate of bromination of benzene droplets in a dense, vigorously agitated aqueous emulsion

Abstract The rate of bromination of benzene droplets by acidified hypobromous acid in a turbulent, dense aqueous emulsion has been analysed theoretically and studied experimentally. The bromination is found to conform to a model in which the reactions are assumed to occur essentially in the continuous medium, the kinetics is chemically controlled, and the species distributed almost thermodynamically between the phases.

Studies in bonding electron density. Part I

The electron-density sections in the planes of the benzene rings of penta-m-phenylene (PMP), hexa-m-phenylene (HMP), and 1:2,5:6,9:10-tribenzocyclododeca-1,5,9-triene-3,7,11-triyne (TTT) have been computed and averaged as well as the sections parallel to the ring planes at a distance of 0·4 A. The results demonstrate σ-density in the centres of the (aromatic) C–C bonds and π-density above the ring planes. Sections passing through the aromatic and exocyclic bonds of the three compounds have been averaged and show ‘π’ density maxima at approximately 0·5 A from their bond centres. The averaged electron-density distribution in the –CC– triple bond of TTT contains a trough of –0·2 e/A3 in the centre as well as ‘π’ peak density of 0·1 e/A3 at 0·6 A distance from the centre of the bond. The anhydrous form of acetylenedicarboxylic acid (ADA) also exhibits a trough in the centre of its –CC– triple bond.