Über lückenlose Ausfüllung desn-dimensionalen Raumes durch kongruente Würfel

Ohne Zusammenfassung     

Structure and photochemistry of 18-diazo-1,4,7,10,13,16-hexaoxacyclononadeca-17,19-dione and its sodium and potassium complexes. Control of the ground-state conformation of 2-diazo-1,3-dicarbonyl fragment via host-guest complexation

[reaction: see text] The macrocyclic 18-diazo-1,4,7,10,13,16-hexaoxacyclononadeca-17,19-dione (3-diazo-2,4-dioxo-19-crown-6, 1) readily forms complexes with potassium (2, stability constant in methanol is K(K+) = 229 +/- 25 M(-1)) and sodium ions (3, K(Na+) = 84.2 +/- 7.9 M(-1) in methanol). According to B3LYP/6-31G+(d,p) calculations and temperature-dependent 1H NMR spectroscopy, the predominant conformation of 1 has a Z,Z arrangement of the diazo and carbonyl groups. The X-ray crystal structure analysis showed that the potassium complex (2) has the same Z,Z arrangement, while the sodium analogue (2) exists in conformation with Z,E geometry of the diazodicarbonyl moiety. Direct 254 nm photolysis of diazo compounds 1-3 in methanol results in the formation of 3-methoxy-2,4-dioxo-19-crown-6 (5), the product of the insertion of corresponding alpha,alpha'-dicarbonylcarbene into the O-H bond of the solvent. The triplet-sensitized photolysis of diazomalonates 1-3 produces 2,4-dioxo-19-crown-6 (6), which is apparently formed via the triplet state of the intervening carbene.     

Capillary electrophoretic determination of lignin degradation products obtained by permanganate oxidation

A new capillary electrophoretic (CE) technique was developed for the separation of lignin degradation products after permanganate oxidation, yielding information about quality and quantity of various linkages in the lignin molecule. This CE method is a promising alternative to existing gas chromatographic (GC) methods. An advantage in comparison with GC is the short separation time and the fact that the oxidation products (aromatic acids) can be analyzed without derivatization. The selectivity and sensitivity of CE combined with UV detection is adequate and makes it suited for fast routine characterization of lignins. If necessary, the CE method can be coupled with electrospray ionization mass spectrometry in order to make a clear assignment of the peaks.     

Elektronenlokalisierung im Grundzustand und in angeregten Zuständen Pars-Orbital-Methode, 12. Mitt

UsingGleason's theorem the pars orbital concept is developed for excited states of conjugated systems described by CI-methods. A significance index is introduced to evaluate different patterns of fragmentation. The usefulness of this approach is illustrated for butadiene, biphenyl, naphthalene, and azulene.

11. Mitt.:H. Karpf, O. E. Polansky undM. Zander, Tetrahedron Lett.1978, 2069.     

Wolff Rearrangement of 2-diazo-1(2H)-naphthalenone induced by nonresonant two-photon absorption of NIR radiation

The irradiation of 2-diazo-1(2H)-naphthalenone (1), the common component of positive photoresists, with 800 nm pulses of ultrafast laser results in Wolff rearrangement via nonresonant two-photon absorbance of light. The 10% conversion of starting material resulting in the formation of methyl 1H-indene-3-carboxylate (2) was achieved after 11 min of irradiation of the methanol solution of 1 with an unfocused beam of a Ti:Sapphire laser operating at 1 kHz. The two-photon cross-section of the diazonaphthoquinone 1 at 800 nm was calculated to be sigma = 2.2 x 10-51 cm4 s photon-1 (0.2 GM).     

New approach to the nonparametric determination of the internal rotation potential from electron diffraction data. Reinvestigation ofm-bromonitrobenzene

A numerical algorithm for the nonparametric determination of the internal rotation potential from electron diffraction data using Tikhonov's regularization method is described. The range of admissible values of the regularization parameter is estimated using Hamilton's statistical criterion. m-Bromonitrobenzene was reinvestigated using this approach. It was found that the form of the potential may be reliably established only in the region of the minimum corresponding to the planar conformation of the molecule. Fourier series approximation of the experimental values of the potential in the region of the minimum gives the rotation barrier of 4.6–5.4 kcal/mole. The following basic geometrical parameters have been obtained (r_a in Å, ∠_α in deg, the error equals triple standard deviation): r(C?C)_ave=1.399(3), r(C?N)=1.459(16), 1.459(16), r(N=O)=1.244(3), r(C?Br)=1.884(6), r(C?H)=1.099(20), ∠CC_NC=123.9(1.4), ∠C_NCCBr=116.8(1.5), ∠C_NCC=116.6(1.9), ∠CNO=118.8(0.8). The results are compared with the data for the related compounds.     

Band structure of even and ions of odd polyenes

The analysis of experimental data for singlet transitions (E _n) of even polyenes (I), cations (II) and anions (III) of odd polyenes show that for infinite chains E (I)/E (II)=E (I)/E (III) = 2:1. It is shown that the energy gap is equal for the three systems. In cases (II) and (III) there is a level (NBMO) in the gap which is vacant in (II) and occupied in (III). That is why the first optical transition in (II) and (III) depends on the semiwidth of the gap.     

SCF perturbation theory for unimolecular reactions

A CNDO/2 SCF perturbation theory is presented for interpreting the form of CNDO/2 potential energy surfaces of unimolecular reactions. The analysis is performed by calculating the energy change E arising from a distortion of the molecular geometry along the reaction coordinate. E is decomposed into different perturbational contributions which are appropriate for an interpretation of the perturbation energy E. Moreover, E is resolved into energy parts arising from a single occupied orbital and contributions due to pairwise orbital interactions. In this way one evaluates numerically how the form of the occupied and unoccupied orbitals determines the magnitude of E. If the distortion occurs along a definite symmetry coordinate, group-theoretical arguments can be applied to discuss the magnitude of characteristic components of the perturbation energy. The SCF perturbation theory is used to analyze the isomerization of ethylene, cis-2-butene and cis-2-butenenitrile.This work was partially supported by Nato-Grant No. 1072     

Practical uses of FTIR spectroscopy in wood science and technology

Based on own research activities this survey demonstrates the potential applications of FTIR spectroscopy in wood and wood-product research. This rapid method can be used e.g. with success for determination of lignin in woody materials and pulps. Crucial analytical data of lignins were also determined by quantitative evaluation of FTIR data. The degree of substitution of cellulose derivatives can be estimated. The course of delignification during pulping was monitored using transmission and circular ATR cells for the IR spectroscopy of the cooking liquors. Based on these spectra the Kappa number of pulps can be predicted.