Bozena Borecka

Control of solid-state photodimerization of trans-cinnamic acid by double salt formation with diamines

By double salt formation, diamines can steer the solid-state [2+2] photodimerization of trans-cinnamic acid (1). Thus, the yields for the photodimerization were significant only in three double salts, i.e., the ones with tn and t- and c-chxn, which are assumed to have an overlap structure. The resultant photodimer is generally β-truxinic acid, although in one case, e-truxillic acid was formed. α-Truxillic acid was not produced from any of the double salts studied. The X-ray crystal structures of three double salts of low photoreactivity (1·en, 1·pen, 1·hen) were consistent with Schmidts rule.

CONTROL OF THE SOLID-STATE PHOTODIMERIZATION OF SOME DERIVATIVES AND ANALOGS OF TRANS-CINNAMIC ACID BY ETHYLENEDIAMINE

Some of double salts derived from ethylenediamine (en) and a variety of trans-cinnamic acids and their analogs underwent photodimerization in the solid state, giving predominantly β-truxinic dimers. X-Ray studies demonstrate that (a) the conformation of en is gauche for the highly photoreactive double salts (o-1b·en and m-1e·en), whereas it is anti for lessphotoreactive o-1a·en or photoinert 1d·en and (b) for highly reactive o-1b·en and m-1e·en, the monomer acid molecules are arranged in an overlap configuration and a reactive monomer pair is hydrogendashbonded to the same en molecule.

Unusual photorearrangements of 9,10-disubstituted triptycene-1,4-quinone derivatives

Abstract In contrast to triptycene-1,4-quinone ( 1a ), which forms exclusively a di-π-methane type product when irradiated in acetonitrile, photolysis of the 9,10-dialkyl-substituted triptycene quinones 1b and 1c leads to carbene-derived as well as hydrogen atom abstraction-derived photoproducts. Mechanistic schemes that are capable of rationalizing the results on stereoelectronic grounds are presented and discussed.

Comparative Electron Density Studies of the Phosphorus-Sulphur Bonding and of the Extent of the Aromatic System in A 1,3,2-Benzodithlaphosphenlum Cation and the Related 2-Phenyl-1,3,2-Benzodithiaphosphole

Abstract The low-temperature X-ray crystal structures of 1,3,2-benzodithia-phosphenium tetrachloraluminate and the corresponding neutral 2-phenyl-1,3,2-benzodithia-phosphole have been determined at 210 K. A comparison of the X-XHO charge density studies for the two systems confirms that the phosphenium cation posseses a planar ‘aromatic’ configuration. However, there are strong indications for a substantial contribution to the structure from a quinoid-like structure with about 60% of the charge localised on the phosphorus atom.

The stability of Carbenic and Alkenic Phosphorus Environments

Abstract The factors responsible for the isolation or identification of (carbenic) phosphenium and (alkenic) tricoordinate phosphonium salts are discussed. Structural features, reactivity and observations of intramolecular rearrangement are presented, which illustrate some of the requirements for stability in each case.

Low-Temperature X-ray Crystal Structure and Electron Density Distribution in the Benzene Clathrate of Hexa(1-Aziridinyl)-Cyclotri(Phosphazene) 2[P3N3(NC2H4)6]C6H6

Abstract The low-temperature X-ray crystal structure of hexa(1 -aziridinyl)-cyclotri(phosphazene) has been determined and refined to R= 0.0341 from data collected to sin(θmax)/λ = 1.0. The various functional groups in the molecule have been examined with X-XHO and deformation density calculations. Clear indications of the expected σ and π bonding electron densities in the benzene ring, of the bent bonding in the three-membered aziridinyl ring and of the lone pair on the aziridinyl nitrogen atoms all help validate the observation of an apparently restricted, delocalised π system in the phosphazene ring.