Helvetica Chimica Acta

doi: 10.1002/hlca.19720550501pmid: N/A

Chardonnens, Louis; Bitsch, Serge

doi: 10.1002/hlca.19720550502pmid: N/A

Starting from 2‐methyl‐ and from 2,3‐dimethyl‐1,4‐diphenyl‐butadiene‐1, 3 respectively, the 5‐methyl‐ and the 5,6‐dimethyl‐11, 12‐dihydro‐indeno[2.1‐a]fluorene are synthesized in 4 steps. The 5, 6‐diphenyl‐11, 12‐dihydro‐indeno[2.1‐a]fluorene is obtained by reduction of the already known 11, 12‐dioxoderivative. Accesorily a new preparation of the unsubstituted hydrocarbon is described.

Krasso, A. F.; Binder, M.; Tamm, Ch.

doi: 10.1002/hlca.19720550503pmid: N/A

The stereochemistry of the epoxycardanolides 8, 21, 24 and 33, derived from digitoxigenin (1), digoxigenin (15), 3β, 14, 15β‐trihydroxy‐5β, 14β‐card‐20(22)‐enolide (23) and gitoxigenin (27) respectively, is discussed on the basis of NMR. data. In the case of 1 and 15 the absolute configuration of the chiral centres C(20) and C(21) is assigned. Treatment of the cardenolides with KOH in methanol gave on dilution with methanol and subsequent acidification a number of acetal derivatives, the properties of which are described.

Dobler, M.

doi: 10.1002/hlca.19720550504pmid: 5068917

An X‐ray crystal structure investigation of the macrotetrolide antibiotic nonactin is reported. The shape of the molecule is discussed with special reference to the conformational changes involved in passing from free nonactin to the K+‐complex.

Heimgartner, H.; Hansen, H.‐J.; Schmid, H.

doi: 10.1002/hlca.19720550505pmid: N/A

1‐cis, 2‐cis‐Dipropenylbenzene (cis, cis‐1) isomerises thermally at 215–235° with 1st order kinetics to give trans, cis‐1 and vice versa. At equilibrium 89% trans, cis‐ and 11% cis, cis‐1 are present. It is shown by thermal rearrangement of cis, cis‐2′, 2″‐d2‐1 that the isomerisation is attributable to aromatic [1, 7a]‐sigmatropic H‐shifts. trans, trans‐1 rearranges thermally at 225–245° to yield 2, 3‐dimethyl‐1, 2‐dihydronaphthalene (2). The formation of 2 can be visualized by disrotatory ring closure followed by an aromatic [1, 5s]‐sigmatropic H‐shift. 2 is also formed when, cis, cis‐ or trans, cis‐1 are heated for 153 h at 225°. Besides 2 a small amount (3%) of 1‐ethyl‐1, 2‐dihydronaphthalene (5) is formed. The rearrangement of trans, trans‐1 and trans, trans‐2′, 2″‐d2‐1 shows a secondary isotope effect kH/kD = 0,90.

Skorianetz, W.; Kováts, E. sz.

doi: 10.1002/hlca.19720550506pmid: N/A

The scheme 1 shows those tetrahydro‐ and dihydroderivatives of the 3,6‐dimethyl‐1,2,4,5‐tetrazine (or s‐tetrazine), 8, which are theoretically possible without considering cis‐trans isomerism, together with the reaction pathways. We did not succeed in synthetizing the 3,6‐dihydroderivative, 7, and could not isolate the 1,2‐dihydrocompound, 4, the latter being probably easily convertible to the thermodynamically more stable 1,4‐dihydro‐s‐tetrazine, 5, via their common conjugate base 4,5B. The 1,4‐dihydro‐s‐tetrazine, 5, gives with 3,6‐dimethyl‐s‐tetrazine 8, a charge transfer complex, 15. The same compounds form in acidic or basic aquious solution stable radicals, 16B and 16S. The mode of formation of these radicals and the subsequent reactions are depicted in scheme 2.

Clark, Patricia A.; Brogli, F.; Heilbronner, E.

doi: 10.1002/hlca.19720550507pmid: N/A

The ‘observed’ π‐orbital energies ϵv,j = −Iv,j derived from the vertical ionization potentials obtained by a photoelectron spectroscopic investigation of the acenes benzene A(1), naphthalene A(2), anthracene A(3), naphthacene A(4) and pentacene A(5) have been compared with π‐orbital energies calculated by three different approximations: (a) the standard Hückel HMO model; (b) a first‐order perturbation treatment, based on (a), that takes into account bond length changes which follow the ionization process; (c) a SCF π‐electron model of the type proposed by Pople and by Pariser & Parr. In agreement with previous experience it is found that model (b) yields the most satisfactory parametrization of the experimental data.

Gübeli, A. O.; Retel, J.‐P.

doi: 10.1002/hlca.19720550508pmid: N/A

The solubility of thallium sulfide in 1M NaClO4 at 25° ranges between 105M as a function of pH and total sulfide concentration.

Reber, J. F.; Fernandez‐Garcia, J. G.; Steiger, R.; Boissonnas, Ch. G.

doi: 10.1002/hlca.19720550509pmid: N/A

The preparation and some properties of large lead halide crystals are described. The photolysis of these crystals was followed by chemical etching (photosolubilization), showing that the rate of solubilization decreases if the crystal is exposed in the presence of oxygen.

Wolf, G.

doi: 10.1002/hlca.19720550510pmid: N/A

The enthalpies of formation of the nine cyclic ketones CnH2n−2O (n = 4–12) were determined by combustion calorimetry. The heats of vaporization were determined by measuring the vapor pressure as a function of temperature and the heats of fusion of the three compounds with n = 8, 9, 12 which are solids at room temperature, by DSC.