Semiempirische LCAO-MO-SCF-Berechnungen von Alkylidenmeldrumsäuren und HMO-Berechnungen von Arylidenmeldrumsäuren und Aryliden-1,3-indandionen

The dipole moments of several alkylideneMeldrum's acids are calculated using the semiempirical LCAO-MO-SCF-method ofPople, and those of some substituted benzylideneMeldrum's acids and indandiones using the HMO-method and a -increment system. On the other hand, these dipole moments are determined experimentally using solutions of these compounds. Agreement between experimental and calculated data is found to be generally good.Differences between the dipole moments, as determined experimentally, of mono- and of di-alkylated methyleneMeldrum's acids indicate different conformations of these compounds.

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1H- und 13C-NMR-spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3-Dioxan-2-ylium-Salzen

The ¹H and ¹³C NMR spectra of a series of 1,3-dioxan-2-ylium salts substituted at C-2 and C-4, C-5, C-6 have been measured. The atomic charge distribution in 1,3-dioxan- and 1,3-dioxolan-2-ylium cations has been calculated with the MINDO/3 method, leading to a linear correlation between π-charge and ¹³C chemical shift at C-2. The strong C-21-proton downfield shift is caused by the anisotropic influence of the mesomeric cation system. The conformations of substituted 1,3-dioxan-2-ylium cations are discussed.     

Zur konformativen Anordnung dipolarer Substituenten in 5-Stellung von 1,3-Dioxanen

Summary The conformation of a series of 5-nitro-1,3-dioxanes, 1,3-dioxane-5-hydroxylamines and the corresponding nitrones, obtained from the latter, has been studied by NMR spectroscopy. In the case of the nitrones, a preferred conformation of the -N(O)CHR ³ substituent to the C⁵, N single bond was found, and it was concluded therefrom on the identical conformational behaviour of the nitro analogoues. A structurally similar spiro compound confirms the suggestions given. In the case of the spiro compound, the intramolecular N-inversion process could be studied by dynamic NMR spectroscopy; the free energy of activation is given.

     

Kombinierte d-NMR- und LIS-Untersuchungen zum konformativen Verhalten von Formylmethylenthiopyranen

The rotational barriers ΔG ^≠ toE,Z- ands-cis, s-trans-isomerisation in formylmethylenthiopyranes are determined and discussed with regard to their dependence on substituent effects. Preferential conformers are distinguished by lanthanide induced shifts. Best fits between calculated and experimental shifts are obtained forE,s-trans andZ,s-cis isomers. The results indicate a nonbonding interaction between aldehyde oxygen and ring sulphur, favourings-cis conformation in case ofZ configuration.     

Dipolmoment und Konformation von Imino-äther-Derivaten

By means of the dipole moments of several imidic acid esters the conformation at the C? O bond and the configuration at the C?N bond have been determined. Use was made of the graphical comparison of a phenyl-derivative with the para-substituted analogue [7] in combination with cyclic model compounds having forced stereochemistry. The results obtained are conclusive for the N-alkyl-derivatives which are in the Eap form A. The imidic acid esters which are unsubstituted at the nitrogen are prevailingly in the same Eap conformation A; another conformation, probably the Zap form B, may also be present in smaller amounts.     

Paramagnetisch verschobene NMR-Spektren und Konformation von isotaktischen und syndiotaktischen Polymethylmethacrylaten

Ohne Zusammenfassung     

Protonen-Spin-Gitter-Relaxation und interne Beweglichkeit von Molekülen

Relaxation rates can be used as assignment tool in NMR-spectroscopy; even conformational changes in the cyclic peptide alkaloid frangulanin (1) can be monitored by proton-relaxation measurements. The results are compared with a force-field calculation of (1).

     

Synthese und polarographisches Verhalten von 2H-Isoindol-4,7-dionen

Summary 2-Phenylthio-1,4-benzoquinone (1 a) reacts with azomethine ylide AY-A to give 2-methyl-5-phenylthio-2H-isoindole-4,7-dione (4 f). With 2-(N-methylanilino)-5-methyl-1,4-benzoquinone (1 b), the azomethine ylide AY-B undergoes cycloaddition to yield an inseparable mixture of 5a-methyl-8-(N-methylanilino)-2,3,5,5a,9a,9b-hexahydro-pyrrolo[2,1-a]1H-isoindole-6,9-dione (5 bI) and 9a-methyl-7-(N-methylanilino)-2,3,5,5a,9a,9b-hexahydropyrrolo[2,1-a]1H-isoindole-6,9-dione (5 bII). The structures of5 bI and5 bII were established on basis of two-dimensional-NMR-techniques. The mechanism of the cycloaddition of azomethine ylides to 1,4-quinones was studied on basis of cyclovoltammetric investigations. To determine the electron affinity of the isoindoledione derivatives4 a–f and5 a–b the peak potentials were measured by differential pulse polarography (DPP).

     

Die Reaktion von 4,6-Dinitroisophthalaldehyd und 4,6-Dinitroisophthalonitril mit Pyridin

The reaction of 4,6-dinitroisophthalaldehyde and 4,6-dinitroisophthalonitrile with pyridine 4, 6-Dinitroisophthalaldehyde ( 4 ) gives on reaction with pyridine 4,6-diformyl-3-(1′-pyridinio)-1-phenolate ( 5 ), whereas 4,6-dinitroisophthalonitrile ( 7 ) gives under the same conditions one main product: 3-(1′)-pyridinio-4, 6-dicyano-1-phenolate ( 10 ) and two side products: 2-(1′-pyridinio)-4, 6-dicyano-3-nitro-1-phenolate ( 11 ) and 4, 6-dicyano-3-nitro-1-phenol ( 12 ). The new structures were elucidated by ¹H-NMR. and ¹³C-NMR. spectroscopy.     

Konformation und physikalische daten von alkanen und cyclanen—V Dimethylcycloheptane

cis-trans-Isomeric dimethylcycloheptanes were prepared in great purity. The best method was found to be the ring expansion of definite alkylcyclohexanone followed by reduction. If tertiary cycloheptanols are dehydrated a rearrangement to 6-membered ring olefins takes place.

A consideration of densities, refractive indices and enthalpies of isomerization of the alkylcycloheptanes shows, that the twist-chair model of cycloheptane, which was established by Allinger and Hendrickson, is in agreement with the experimental values. All isomers with the exception of 1,1-dimethylcycloheptane and cis-1,2-dimethylcycloheptane have a quasi-diequatorial arrangement. The enthalpy of isomerization between cis- and trans-1,2-dimethylcycloheptane is 0·7 kcal/mole.     

Konfigurationen und Konformationen von zwei 2,4,6,8-Tetrabrom-cyclooctan-1, 5-dionen

The two isomeric tetrabromides, α-isomer mp. 198° and β-isomer mp. 226° described in [1], are identified as cis, cis, trans-2, 4, 6, 8-tetrabromo-cyclooctane-1, 5-dione ( 2 ) and cis, trans, cis-2, 4, 6, 8-tetrabromo-cyclooctane-1, 5-dione ( 3 ) by an analysis of their NMR.-spectra which also allows a derivation of their preferred conformations. Both exist in solution as boat-chair conformers, the geometries of which correlate well with the IR.- and UV.-spectra.