Further studies on palytoxin. I.

The structures of two degradation products of N-(p-bromobenzoyl) palytoxin were elucidated, and then the sequences of those fragments were determined.     

Perfluoroalkylene-linked aromatic polyimides. II. Further property studies

The synthesis and general physical characteristics of the perfluoroalkylene-linked aromatic polyimides have been discussed in Part I. In this paper the hydrolytic, oxidative, and thermal stabilities of these polymers are compared with those of certain wholly aromatic polyimides. Comparative studies are also made on the effect of the fluoroalkylene chain on the glass transition temperatures. The polymer from di-(4-aminophenyl) ether and 1,3-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride has been studied in most detail and various mechanical and electrical properties of this polymer in film and solid molded form are discussed.     

Structural studies on palytoxin,a potent coelenterate toxin

The structural elucidation of palytoxin is reported.     

Further studies on chromium(II)-mediated homoallylic alcohol syntheses

The stereochemical outcome of chromium(II)-mediated syntheses of homoallylic alcohols has been examined on 11 aldehydes, $\text{3a}$ – $\text{13a}$.     

Synthetic studies on palytoxin. Stereocontrolled,practical synthesis of the C.101–C.115 segment

A stereocontrolled and practical synthetic route to the acetal $\text{2a}$, a degradation product of palytoxin, in optically active form is described.     

Friedel-crafts cyclisations. II. Further studies of polyphosphoric acid-catalysed cyclisations of N-cinnamoyl derivatives of aromatic amines

Further studies of the effects of substituents in the N-phenyl nucleus on the polyphosphoric acid-catalysed cyclisation of cinnamanilide to 4-phenyl-3,4-dihydrocarbostyril have confirmed that the isomerisation is prevented by a nitro group and retarded by other substituents in the ortho position to the NH- group. Although a methyl group ortho to the only position at which cyclisation can occur was also shown to retard the reaction, N-cinnamoyl-2,4,5-trichloroaniline was cyclised in moderate yield after prolonged heating, but the 2,4-dibromo and 2,5-dimethoxy analogues were not isomerised. Isomerisation of 2-cinnamamidobiphenyl to 4,8-diphenyl-3,4-dihydrocarbostyril was accompanied by cyclodehydration to 6-styrylphenanthridine. Five new derivatives of cinnamanilide and eight new derivatives of 4-phenyl-3,4-dihydrocarbostyril are described.     

Structural studies of polyformals. II. Crystal structure of poly-1,3-dioxolane: Modification II1

The structure of poly-1,3-dioxolane, [? OCH₂O? (CH₂)₂? ]_n was studied by x-ray diffraction and infrared spectroscopy. Three crystal modifications were found. The crystal structure of modification II was determined: four molecular chains of glide type pass through the orthorhombic unit cell; Pbca-D_2h¹⁵, a = 9.07 Å, b = 7.79 Å, and c (fiber axis) = 9.85Å. The molecular conformation is The molecular chain consists of regular head-to-tail sequences. This fact shows that the ring opening of 1,3-dioxolane occurs exclusively at the same type of CO bond in the cationic polymerization, just as in the case of 1,3-dioxepane.     

二十面体对称性(I~h)分子的从头计算研究II. 铜原子簇Cu~13的电子结构

应用对称性约化计算方案, 完成了铜原子簇Cu~13(I~h)三种基组下的从头计算, 最大维数390。为了进行比较, 也进行了Cu~2、Cu~4、Cu~6及Cu~8的计算。经过优化, 获得基态及平衡几何、布居、结合能等数据, 表明Cu~13可能稳定存在。Cu~13中以d成分为主的分子轨道均已填满, 对化学键无实际贡献, 成键作用为s, p性质; 再者, d带与s带不相交叠, 无金属Cu能带的特征。无论平衡几何、布居及结合能数值均与采用的其组很有关系, 虽然定性趋势是一致的。     

Further theoretical studies of the structure and electronic spectrum of cyclobutadiene

The possible geometries for cyclobutadiene and the electronic spectra corresponding to those geometries were calculated by a modified Pariser-Parr method with inclusion of doubly-excited as well as singly-excited configurations in calculating the -energy. The bond lengths of the most stable forms agreed well with previous calculations where the empirical parameters used in the -energy calculation were different from those used here, and where only singly-excited configurations were included. With these additional refinements, the rectangular singlet is calculated to be more stable than the square triplet. It is noted that the geometry predicted to have the lowest energy is a function of the approximations employed.

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Zusammenfassung Mögliche Geometrien und die zugehörigen Spektren von Cyclobutadien wurden nach Pariser-Parr unter Einschlu\ der einfach und zweifach angeregten Konfigurationen berechnet. Die BindungslÄngen der stabilsten Form stimmen gut mit früheren Rechnungen mit anderen gewÄhlten Parametern überein, bei denen nur die einfach angeregten Konfigurationen berücksichtigt worden waren. Und zwar ergibt sich, da\ eine rechteckige Form (Singulett) stabiler als die quadratische (Triplett) ist. Allerdings hÄngt diese Geometrie von den gewÄhlten Parametern ab.

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Résumé Les geometries possibles du butadiéne et les spectres électroniques correspondants ont été calculés par une méthode de Pariser-Parr motifiée avec interaction de configurations avec les états mono et diexcités des électrons . Les longueurs de liaison des formes les plus stables sont en accord avec celles obtenues précédemment avec des paramètres empiriques différents dans un calcul ne tenant compte que des configurations monoexcitées. Dans notre calcul amélioré le singulet rectangulaire est plus stable que le triplet carré. La géométrie la plus stable dépend de l'approximation utilisée.

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This research was supported in part by Research Grant GP 4290 from the National Science Foundation.     

Further studies on hydroxyperezone derivatives

Hydroxyperezone monoangelate (2c) was transformed into the mixture of α-(8) and β-perezols (9). Separation of these compounds permitted stereochemical assignments by NMR and ORD. The position of the angeloyl moiety in 2c was independently tested by its conversion to O-methylhydroxyperezone (1d) identified with a sample synthesised from perezone (1a). Several reactions distinguished the natural hydroxyperezone (2a) from the synthetic hydroxyperezone hydrate (3).     

Further synthetic studies on rifamycin s

Two new highly stereocontrolled syntheses of the optically active form of the aliphatic segment 2 of rifamycin S are described.